	Editors: T Bealea
Revision: 2.0.1	Pages: 59	Date of issue: 20 Mar 2007

EHR Extract
EHR	Demographic	Integration	Template OM
Composition	openEHR Archetype Profile
Security	Common	Archetype OM		ADL

Data Structures
Data Types
Support

Founding	David Ingram, Professor of Health Informatics,
Chairman	CHIME, University College London
Founding	Dr P Schloeffel, Dr S Heard, Dr D Kalra, D Lloyd, T Beale
Members
	email: info@openEHR.org web: http://www.openEHR.org

Copyright Notice

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Date of Issue: 20 Mar 2007 Page 2 of 59 Editors:T Beale

Amendment Record

Issue	Details	Raiser	Completed
	R E L E A S E 1.0.1
2.0.1	CR-000200. Correct Release 1.0 typographical errors. Table for missed class ASSERTION_VARIABLE added. Assumed_value assertions corrected; standard_representation function corrected. Added missed adl_version, concept rename from CR-000153. CR-000216: Allow mixture of W, D etc in ISO8601 Duration (deviation from standard). CR-000219: Use constants instead of literals to refer to terminology in RM. CR-000232. Relax validity invariant on CONSTRAINT_REF. CR-000233: Define semantics for occurrences on ARCHETYPE_INTERNAL_REF. CR-000234: Correct functional semantics of AOM constraint model package. CR-000245: Allow term bindings to paths in archetypes.	D Lloyd, P Pazos, R Chen, C Ma S Heard R Chen R Chen K Atalag T Beale S Heard	20 Mar 2007
	R E L E A S E 1.0
2.0	CR-000153. Synchronise ADL and AOM attribute naming. CR-000178. Add Template Object Model to AM. Text changes only. CR-000167. Add AUTHORED_RESOURCE class. Remove description package to resource package in Common IM.	T Beale T Beale T Beale	10 Nov 2005
	R E L E A S E 0.96
0.6	CR-000134. Correct numerous documentation errors in AOM. Including cut and paste error in TRANSLATION_DETAILS class in Archetype package. Corrected hyperlinks in Section 2.3. CR-000142. Update ADL grammar to support assumed values. Changed C_PRIMITIVE and C_DOMAIN_TYPE. CR-000146: Alterations to am.archetype.description from CEN MetaKnow CR-000138. Archetype-level assertions. CR-000157. Fix names of OPERATOR_KIND class attributes	D Lloyd S Heard, T Beale D Kalra T Beale T Beale	20 Jun 2005
	R E L E A S E 0.95
0.5.1	Corrected documentation error -return type of ARCHETYPE_CONSTRAINT.has_path; add optionality markers to Primitive types UML diagram. Removed erroneous aggregation marker from ARCHETYPE_ONTOLOGY.parent_archetype and ARCHETYPE_DESCRIPTION.parent_archetype.	D Lloyd	20 Jan 2005
0.5	CR-000110. Update ADL document and create AOM document. Includes detailed input and review from: - DSTC - CHIME, Uuniversity College London - Ocean Informatics Initial Writing. Taken from ADL document 1.2draft B.	T Beale A Goodchild Z Tun T Austin D Kalra N Lea D Lloyd S Heard T Beale	10 Nov 2004

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Archetype Object Model

Rev 2.0.1

Trademarks

Microsoft is a trademark of the Microsoft Corporation

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Archetype Object Model

Rev 2.0.1

1 Introduction.............................................................................. 7

1.1 Purpose...................................................................................................7

1.3 Nomenclature.........................................................................................7

1.4 Status......................................................................................................7

1.5 Background............................................................................................7

1.5.1 What is an Archetype?.....................................................................7

1.5.2 Context.............................................................................................8

1.6 Tools.......................................................................................................8

1.7 Changes from Previous Versions ...........................................................8

1.7.1 Version 0.6 to 2.0.............................................................................8

2 The Archetype Object Model.................................................. 9

2.1 Design Background................................................................................9

2.2 Package Structure...................................................................................9

2.3 Model Overview ..................................................................................10

2.3.1 Archetypes as Objects....................................................................10

2.3.2 The Archetype Ontology ...............................................................11

2.3.3 Archetype Specialisation ...............................................................12

2.3.4 Archetype Composition.................................................................12

3 The Archetype Package......................................................... 13

3.1 Overview..............................................................................................13

3.2 Class Descriptions................................................................................14

3.2.1 ARCHETYPE Class ......................................................................14

3.2.2 VALIDITY_KIND Class ...............................................................16

4 Constraint Model Package.................................................... 17

4.1 Overview..............................................................................................17

4.2 Semantics .............................................................................................17

4.2.1 All Node Types ..............................................................................17

4.2.2 Attribute Node Types.....................................................................17

4.2.3 Object Node Types ........................................................................19

4.2.4 Assertions ......................................................................................21

4.3 Class Definitions..................................................................................22

4.3.1 ARCHETYPE_CONSTRAINT Class...........................................22

4.3.2 C_ATTRIBUTE Class ...................................................................23

4.3.3 C_SINGLE_ATTRIBUTE Class...................................................23

4.3.4 C_MULTIPLE_ATTRIBUTE Class..............................................23

4.3.5 CARDINALITY Class ..................................................................24

4.3.6 C_OBJECT Class ..........................................................................25

4.3.7 C_DEFINED_OBJECT Class .......................................................25

4.3.8 C_COMPLEX_OBJECT Class .....................................................26

4.3.9 C_PRIMITIVE_OBJECT Class ....................................................27

4.3.10 C_DOMAIN_TYPE Class.............................................................27

4.3.11 C_REFERENCE_OBJECT Class .................................................27

4.3.12 ARCHETYPE_SLOT Class ..........................................................28

4.3.13 ARCHETYPE_INTERNAL_REF Class.......................................28

4.3.14 CONSTRAINT_REF Class...........................................................29

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Archetype Object Model

Rev 2.0.1

5 The Assertion Package .......................................................... 31

5.1 Overview ............................................................................................. 31

5.2 Semantics............................................................................................. 31

5.3 Class Descriptions ............................................................................... 32

5.3.1 ASSERTION Class ....................................................................... 32

5.3.2 EXPR_ITEM Class ....................................................................... 32

5.3.3 EXPR_LEAF Class.......................................................................33

5.3.4 EXPR_OPERATOR Class ............................................................33

5.3.5 EXPR_UNARY_OPERATOR Class ............................................ 34

5.3.6 EXPR_BINARY_OPERATOR Class ........................................... 34

5.3.7 ASSERTION_VARIABLE Class..................................................35

5.3.8 OPERATOR_KIND Class.............................................................36

6 The Primitive Package........................................................... 39

6.1 Overview ............................................................................................. 39

6.2 Class Descriptions ............................................................................... 40

6.2.1 C_PRIMITIVE Class .................................................................... 40

6.2.2 C_BOOLEAN Class .....................................................................40

6.2.3 C_STRING Class .......................................................................... 41

6.2.4 C_INTEGER Class .......................................................................41

6.2.5 C_REAL Class .............................................................................. 42

6.2.6 C_DATE Class .............................................................................. 42

6.2.7 C_TIME Class...............................................................................43

6.2.8 C_DATE_TIME Class................................................................... 44

6.2.9 C_DURATION Class .................................................................... 47

7 Ontology Package .................................................................. 49

7.1 Overview ............................................................................................. 49

7.2 Semantics............................................................................................. 49

7.3 Class Descriptions ............................................................................... 50

7.3.1 ARCHETYPE_ONTOLOGY Class .............................................50

7.3.2 ARCHETYPE_TERM Class......................................................... 52

A Domain-specific Extension Example.................................... 53

A.1 Overview ............................................................................................. 53

A.2 Scientific/Clinical Computing Types .................................................. 53

B Using Archetypes with Diverse Reference Models ............. 55

B.1 Overview ............................................................................................. 55

B.2 Clinical Computing Use ...................................................................... 55

C References............................................................................... 57

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Archetype Object Model Introduction Rev 2.0.1

Introduction

1.1 Purpose

This document contains the definitive statement of archetype semantics, in the form of an object model for archetypes. The model presented here can be used as a basis for building software that processes archetypes, independent of their persistent representation; equally, it can be used to develop the output side of parsers that process archetypes in a linguistic format, such as the openEHR Archetype Definition Language (ADL) [4] , XML-instance and so on. As a specification, it can be treated as an API for archetypes.

It is recommended that the openEHR ADL document [4] be read in conjunction with this document, since it contains a detailed explanation of the semantics of archetypes, and many of the examples are more obvious in ADL, regardless of whether ADL is actually used with the object model presented here or not.

1.2 Related Documents

Prerequisite documents for reading this document include:

• The openEHR Architecture Overview Related documents include:

The openEHR Archetype Definition Language (ADL)
The openEHR Archetype Profile (oAP)

1.3 Nomenclature

In this document, the term ‘attribute’ denotes any stored property of a type defined in an object model, including primitive attributes and any kind of relationship such as an association or aggregation. XML ‘attributes’ are always referred to explicitly as ‘XML attributes’.

1.4 Status

This document is under development, and is published as a proposal for input to standards processes and implementation works.

This document is available at http://svn.openehr.org/specification/TAGS/Release 1.0.1/publishing/architecture/am/aom.pdf.

The latest version of this document can be found at http://svn.openehr.org/specifica tion/TRUNK/publishing/architecture/am/aom.pdf.

Blue text indicates sections under active development.

1.5 Background

1.5.1 What is an Archetype?

Archetypes are constraint-based models of domain entities, or what some might call “structured business rules”. Each archetype describes configurations of data instances whose classes are described in a reference model; the instance configurations are considered to be valid exemplars of a particular

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Introduction Archetype Object Model Rev 2.0.1

domain concept. Thus, in medicine, an archetype might be designed to constrain configurations of instances of a simple node/arc information model, that express a “microbiology test result” or a “physical examination”. Archetypes can be composed, specialised, and templated for local use. The archetype concept has been described in detail by Beale [1], [2]. Most of the detailed formal seman tics are described in the openEHR Archetype Definition Language [4] . The openEHR archetype framework is described in terms of Archetype Definitions and Principles [4] and an Archetype Sys tem [5] .

1.5.2 Context

The object model described in this document relates to linguistic forms of archetypes as shown in FIGURE 1. The model (upper right in the figure) is the object-oriented semantic equivalent of the ADL the Archetype Definition Language BNF language definition, and, by extension, any formal transformation of it. Instances of the model (lower right on the figure) are themselves archetypes, and correspond one-to-one with archetype documents expressed in ADL or a related language.

archetype language

Archetype object

definition (EBNF)

XML-schema

IDL

other concrete

formalisms

FIGURE 1 Relationship of Archetype Object Model to Archetype Languages

1.6 Tools

Various tools exist for creating and processing archetypes. The openEHR tools are available in source and binary form from the website ( http://www.openEHR.org ).

1.7 Changes from Previous Versions

1.7.1 Version 0.6 to 2.0

As part of the changes carried out to ADL version 1.3, the archetype object model specified here is revised, also to version 2.0, to indicate that ADL and the AOM can be regarded as 100% synchronised specifications.

added a new attribute adl_version: String to the ARCHETYPE class;
changed name of ARCHETYPE.concept_code attribute to concept.

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The Archetype Object Model

2.1 Design Background

An underpinning principle of openEHR is the use of archetypes and templates, which are formal models of domain content, and are used to control data structure and content during creation, modificatoin and querying. The elements of this architecture are twofold.

The openEHR Reference Model (RM), defining the structure and semantics of information in terms of information models (IMs). The RM models correspond to the ISP RM/ODP information viewpoint, and define the data of openEHR EHR systems. The information model is designed to be invariant in the long term, to minimise the need for software and schema updates.
The openEHR Archetype Model (AM), defining the structure and semantics of archetypes and templates. The AM consists of the archetype language definition language (ADL), the Archetype Object Model (AOM) and the openEHR Archetype profile (oAP).

The purpose of ADL is to provide an abstract syntax for textually expressing archetypes and templates. The AOM defines the object model equivalent, in terms of a UML model. It is a generic model, meaning that it can be used to express archetypes for any reference model in a standard way. ADL and the AOM are brought together in an ADL parser: a tool which can read ADL archetype texts, and whose parse-tree (resulting in-memory object representation) is instances of the AOM. The TOM defines the object model of templates, which are themselves used to put archetypes together into local information structures, usually corresponding to screen forms.

The purpose of the openEHR Archetype Profile is to define which classes and attributes of the openEHR RM can be sensibly archetyped, and to provide custom archetype classes.

2.2 Package Structure

The openEHR Archetype Object Model is defined as the package am.archetype, as illustrated in FIGURE 2 . It is shown in the context of the openEHR am.archetype packages.

FIGURE 2 openehr.am.archetype Package

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2.3 Model Overview

The model described here is a pure object-oriented model that can be used with archetype parsers and software that manipulates archetypes. It is independent of any particular linguistic expression of an archetype, such as ADL or OWL, and can therefore be used with any kind of parser.

It is dependent on the openEHR Support model (assumed types and identifiers), as small number of the openEHR Data types IM, and the AUTHORED_RESOURCE classes from the openEHR Common IM.

2.3.1 Archetypes as Objects

FIGURE 3 illustrates various processes that can be responsible for creating an archetype object structure, including parsing, database retrieval and GUI editing. A parsing process that would typically turn a syntax expression of an archetype (ADL, XML, OWL) into an object one. The input file is converted by a parser into an object parse tree, shown on the right of the figure, whose types are specified in this document. Database retrieval will cause the reconstruction of an archetype in memory from a structured data representation, such as relational data, object data or XML. Direct in-memory editing by a user with a GUI archetype editor application will cause on-the-fly creation and destruction of parts of an archetype during the editing session, which would eventually cause the archetype to be stored in some form when the user decides to commit it.

After initial parsing, the in-memory representation is then validated by the semantic checker of the ADL parser, which can verify numerous things, such as that term codes referenced in the definition section are defined in the ontology section. It can also validate the classes and attributes mentioned in the archetype against a specification for the relevant information model (e.g. in XMI or some equivalent)

information model specification

description

archetype

binding

key

C_attribute (single)

constraint_ref

use_reference

C_complex_object

C_primitive_object

archetype_slot

C_attribute (container)

FIGURE 3 Archetype Parsing Process

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Archetype Object Model The Archetype Object Model Rev 2.0.1

As shown in the figure, the definition part of the in-memory archetype consists of alternate layers of object and attribute constrainer nodes, each containing the next level of nodes. In this document, the word ‘attribute’ refers to any data property of a class, regardless of whether regarded as a ‘relationship’ (i.e. association, aggregation, or composition) or ‘primitive’ (i.e. value) attribute in an object model. At the leaves are primitive object constrainer nodes constraining primitive types such as String, Integer etc. There are also nodes that represent internal references to other nodes, constraint reference nodes that refer to a text constraint in the constraint binding part of the archetype ontology, and archetype constraint nodes, which represent constraints on other archetypes allowed to appear at a given point. The full list of concrete node types is as follows:

C_complex_object: any interior node representing a constraint on instances of some non-primitive type, e.g. ENTRY, SECTION;

C_attribute: a node representing a constraint on an attribute (i.e. UML ‘relationship’ or ‘primitive attribute’) in an object type;

C_primitive_object: an node representing a constraint on a primitive (built-in) object type;

Archetype_internal_ref: a node that refers to a previously defined object node in the same archetype. The reference is made using a path;

Constraint_ref: a node that refers to a constraint on (usually) a text or coded term entity, which appears in the ontology section of the archetype, and in ADL, is referred to with an “acNNNN” code. The constraint is expressed in terms of a query on an external entity, usually a terminology or ontology;

Archetype_slot: a node whose statements define a constraint that determines which other archetypes can appear at that point in the current archetype. It can be thought of like a keyhole, into which few or many keys might fit, depending on how specific its shape is. Logically it has the same semantics as a C_COMPLEX_OBJECT, except that the constraints are expressed in another archetype, not the current one.

The typename nomenclature “C_complex_object”, “C_primitive_object”, “C_attribute” used here is intended to be read as “constraint on xxxx”, i.e. a “C_complex_object” is a “constraint on a complex object (defined by a complex reference model type)”. These typenames are used below in the formal model.

2.3.2 The Archetype Ontology

There are no linguistic entities at all in the definition part of an archetype, with the possible exception of constraints on text items which might have been defined in terms of regular expression patterns or fixed strings. All linguistic entities are defined in the ontology part of the archetype, in such a way as to allow them to be translated into other languages in convenient blocks. As described in the openEHR ADL document, there are four major parts in an archetype ontology: term definitions, constraint definitions, term bindings and constraint bindings. The former two define the meanings of various terms and textual constraints which occur in the archetype; they are indexed with unique identifiers which are used within the archetype definition body. The latter two ontology sections describe the mappings of terms used internally to external terminologies. Due to the well-known problems with terminologies (described in some detail in the openEHR ADL document, and also by

e.g. Rector [6] and others), mappings may be partial, incomplete, approximate, and occasionally, exact.

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2.3.3 Archetype Specialisation

Archetypes can be specialised. The formal rules of specialisation are described in the openEHR Archetype Semantics document (forthcoming), but in essence are easy to understand. Briefly, an archetype is considered a specialisation of another archetype if it mentions that archetype as its parent, and only makes changes to its definition such that its constraints are ‘narrower’ than those of the parent. Any data created via the use of the specialised archetype is thus conformant both to it and its parent. This notion of specialisation corresponds to the idea of ‘substitubility’, applied to data.

Every archetype has a ‘specialisation depth’. Archetypes with no specialisation parent have depth 0, and specialised archetypes add one level to their depth for each step down a hierarchy required to reach them.

2.3.4 Archetype Composition

It the interests of re-use and clarity of modelling, archetypes can be composed to form larger structures semantically equivalent to a single large archetype. Composition allows two things to occur: for archetypes to be defined according to natural ‘levels’ or encapsulations of information, and for the reuse of smaller archetypes by a multitude of others. Archetype slots are the means of composition, and are themselves defined in terms of constraints.

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Archetype Object Model The Archetype Package Rev 2.0.1

The Archetype Package

3.1 Overview

The model of an archetype, illustrated in FIGURE 4, is straightforward at an abstract level, mimick ing the structure of an archetype document as defined in the openEHR Archetype Definition Language (ADL) document. An archetype is a modelled as a particular kind of AUTHORED_RESOURCE, and as such, includes descriptive meta-data, language information and revision history. The ARCHETYPE class adds identifying information, a definition - expressed in terms of constraints on instances of an object model, and an ontology. The archetype definition, the ‘main’ part of an archetype, is an

AUTHORED_RESOURCE

(rm.common.resource)

FIGURE 4 openehr.am.archetype Package

instance of a C_COMPLEX_OBJECT, which is to say, the root of the constraint structure of an archetype always takes the form of a constraint on a non-primitive object type. The last section of an archetype, the ontology, is represented by its own class, and is what allows the archetypes to be natural language- and terminology-neutral.

A utility class, VALIDITY_KIND is also included in the Archetype package. This class contains one integer attribute and three constant definitions, and is intended to be used as the type of any attribute in this constraint model whose value is logically ‘mandatory’, ‘optional’, or ‘disallowed’. It is used in this model in the classes C_Date, C_Time and C_Date_Time.

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3.2 Class Descriptions

3.2.1 ARCHETYPE Class

© 2004-2007 The openEHR Foundation. email: info@openEHR.org web: http://www.openEHR.org
CLASS	ARCHETYPE
Purpose	Archetype equivalent to ARCHETYPED class in Common reference model. Defines semantics of identfication, lifecycle, versioning, composition and specialisation.
Inherit	AUTHORED_RESOURCE
Attributes	Signature	Meaning
0..1	adl_version: String	ADL version if archteype was read in from an ADL sharable archetype.
1..1	archetype_id: ARCHETYPE_ID	Multi-axial identifier of this archetype in archetype space.
0..1	uid: HIER_OBJECT_ID	OID identifier of this archetype.
1..1	concept: String	The normative meaning of the archetype as a whole, expressed as a local archetype code, typically “at0000”.
0..1	parent_archetype_id: ARCHETYPE_ID	Identifier of the specialisation parent of this archetype.
1..1	definition: C_COMPLEX_OBJECT	Root node of this archetype
1..1	ontology: ARCHETYPE_ONTOLOGY	The ontology of the archetype.
0..1	invariants: Set<ASSERTION>	Invariant statements about this object. Statements are expressed in first order predicate logic, and usually refer to at least two attributes.
Functions	Signature	Meaning
1..1	version: String previous_version: String	Version of this archetype, extracted from id. Version of predecessor archetype of this archetype, if any.
0..1	version: String previous_version: String
1..1	short_concept_name: String	The short concept name of the archetype extracted from the archetype_id.
	concept_name (a_lang: String): String	The concept name of the archetype in language a_lang; corresponds to the term definition of the concept attribute in the archetype ontology.

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CLASS
1..1	physical_paths: Set<String>	Set of language-independent paths extracted from archetype. Paths obey Xpath-like syntax and are formed from alternations of C_OBJECT.node_id and C_ATTRIBUTE.rm_attribute_name values.
	logical_paths (a_lang: String): Set<String>	Set of language-dependent paths extracted from archetype. Paths obey the same syntax as physical_paths, but with node_ids replaced by their meanings from the ontology.
1..1	is_specialised: Boolean ensure Result implies parent_archetype_id /= Void	True if this archetype is a specialisation of another.
1..1	specialisation_depth: Integer ensure Result = ontology. specialisation_depth	Specialisation depth of this archetype; larger than 0 if this archetype has a parent. Derived from ontology.specialisation_depth.
	node_ids_valid: Boolean	True if every node_id found on a C_OBJECT node is found in ontology.term_codes.
	internal_references_valid: Boolean	True if every ARCHETYPE_INTERNAL_REF. target_path refers to a legitimate node in the archetype definition.
	constraint_references_valid: Boolean	True if every CONSTRAINT_REF.reference found on a C_OBJECT node in the archetype definition is found in ontology.constraint_codes.
	is_valid: Boolean ensure not (node_ids_valid and internal_references_valid and constraint_references_valid) implies not Result	True if the archetype is valid overall; various tests should be used, including checks on node_ids, internal references, and constraint references.

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Rev 2.0.1

archetype_id_validity: archetype_id /= Void concept_valid: ontology.has_term_code(concept_code) uid_validity: uid /= Void implies not uid.is_empty version_validity: version /= Void and then version.is_equal(archetype_id.version_id) original_language_valid: original_language /= void and then language /= Void and then code_set(Code_set_id_languages).has_code(original_language) description_exists: description /= Void definition_exists: definition /= Void ontology_exists: ontology /= Void Specialisation_validity: is_specialised implies specialisation_depth > 0 Invariants_valid: invariants /= Void implies not invariants.is_empty

3.2.2 VALIDITY_KIND Class

CLASS	VALIDITY_KIND
Purpose	An enumeration of three values which may commonly occur in constraint models.
Use	Use as the type of any attribute within this model, which expresses constraint on some attribute in a class in a reference model. For example to indicate validity of Date/Time fields.
Attributes	Signature	Meaning
1..1	const mandatory: Integer = 1001	Constant to indicate mandatory presence of something
1..1	const optional: Integer = 1002	Constant to indicate optional presence of something
1..1	const disallowed: Integer = 1003	Constant to indicate disallowed presence of something
1..1	value: Integer	Actual value
Functions	Signature	Meaning
	valid_validity (a_validity: Integer): Boolean ensure a_validity >= mandatory and a_validity <= disallowed	Function to test validity values.
Invariant	Validity: valid_validity(value)

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Archetype Object Model Constraint Model Package Rev 2.0.1

Constraint Model Package

4.1 Overview

FIGURE 5 illustrates the class model of an archetype definition. This model is completely generic, and is designed to express the semantics of constraints on instances of classes which are themselves described in UML (or a similar object-oriented meta-model). Accordingly, the major abstractions in this model correspond to major abstractions in object-oriented formalisms, including several variations of the notion of ‘object’ and the notion of ‘attribute’. The notion of ‘object’ rather than ‘class’ or ‘type’ is used because archetypes are about constraints on data (i.e. ‘instances’, or ‘objects’) rather than models, which are constructed from ‘classes’.

An informal way of understanding the model is as follows. An archetype definition is an instance of a C_COMPLEX_OBJECT, which can be thought of as expressing constraints on a object that is of some particular reference model type (recorded in the attribute rm_type_name), and which is larger than a simple instance of a primitive type such as String or Integer. The constraints define what configurations of reference model class instances are considered to conform to the archetype. For example, certain configurations of the classes PARTY, ADDRESS, CLUSTER and ELEMENT might be defined by a Person archetype as allowable structures for ‘people with identity, contacts, and addresses’. Because the constraints allow optionality, cardinality and other choices, a given archetype usually corresponds to a set of similar configurations of objects. At the leaf nodes of an archetype definition are C_PRIMITIVE_OBJECT nodes, defining the constraints on leaf values of objects, i.e. Integers, Strings etc.

4.2 Semantics

The effect of the model is to create archetype description structures that are a hierarchical alternation of object and attribute constraints, as shown in FIGURE 3. This structure can be seen by inspecting an ADL archetype, or by viewing an archetype in the openEHR ADL workbench [9], and is a direct con sequence of the object-oriented principle that classes consist of properties, which in turn have types that are classes. (To be completely correct, types do not always correspond to classes in an object model, but it does not make any difference here). The repeated object/attribute hierarchical structure of an archetype provides the basis for using paths to reference any node in an archetype. Archetype paths follow a syntax that is a subset of the W3C Xpath syntax.

4.2.1 All Node Types

A small number of properties are defined for all node types. The path feature computes the path to the current node from the root of the archetype, while the has_path function indicates whether a given path can be found in an archetype. The is_valid function indicates whether the current node and all subnodes are internally valid according to the semantics of this archetype model. The is_subset_of function is used for comparison between corresponding nodes from different archetypes, in order to asert specialisation.

4.2.2 Attribute Node Types

Constraints on attributes are represented by instances of the two subtypes of C_ATTRIBUTE: C_SINGLE_ATTRIBUTE and C_MULTIPLE_ATTRIBUTE. For both subtypes, the common constraint is

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constraint_model

ARCHETYPE_CONSTRAINT

is_valid: Boolean has_path(a_path: String): Boolean path: String is_subset_of (other: ARCHETYPE_CONSTRAINT): Boolean

FIGURE 5 openehr.am.archetype.constraint_model Package

Archetype Object Model Constraint Model Package Rev 2.0.1

whether the corresponding instance (defined by the rm_attribute_name attribute) must exist. Both subtypes have a list of children, representing constraints on the object value(s) of the attribute.

Single-valued attributes (such as Person.date_of_birth: Date) are constrained by instances of the type C_SINGLE_ATTRIBUTE, which uses the children to represent multiple alternative object constraints for the attribute value.

Multiply-valued attributes (such as Person.contacts: List<Contact>) are constrained by an instance of C_MULTIPLE_ATTRIBUTE, which allows multiple co-existing member objects of the container value of the attribute to be constrained, along with a cardinality constraint, describing ordering and unique ness of the container. FIGURE 6 illustrates the two possibilities.

(PERSON.address as structured or free text form)

FIGURE 6 Single and Multiple-valued C_ATTRIBUTES

The need for both existence and cardinality constraints in the C_MULTIPLE_ATTRIBUTE class deserves some explanation, especially as the meanings of these notions are often confused in object-oriented literature. An existence constraint indicates whether an object will be found in a given attribute field, while a cardinality constraint indicates what the valid membership of a container object is. Cardinality is only required for container objects such as List<T>, Set<T> and so on, whereas existence is always required. If both are used, the meaning is as follows: the existence constraint says whether the container object will be there (at all), while the cardinality constraint says how many items must be in the container, and whether it acts logically as a list, set or bag.

4.2.3 Object Node Types

Node_id and Paths

The node_id attribute in the class C_OBJECT, inherited by all subtypes, is of great importance in the archetype constraint model. It has two functions:

it allows archetype object constraint nodes to be individually identified, and in particular, guarantees sibling node unique identification;
it is the main link between the archetype definition (i.e. the constraints) and the archetype ontology, because each node_id is a ‘term code’ in the ontology.

The existence of node_ids in an archetype allows archetype paths to be created, which refer to each node. Not every node in the archetype needs a node_id, if it does not need to be addressed using a path; any leaf or near-leaf node which has no sibling nodes from the same attribute can safely have no node_id.

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4.2.3.1 Defined Object Nodes (C_DEFINED_OBJECT)

The C_DEFINED_OBJECT subtype corresponds to the category of C_OBJECTs that are defined in an archetype by value, i.e. by inline definition. Four properties characterise C_DEFINED_OBJECTs as follows.

Any_allowed

The any_allowed function a node indicates that any value permitted by the reference model for the attribute or type in question is allowed by the archetype; its use permits the logical idea of a completely “open” constraint to be simply expressed, avoiding the need for any further substructure. Any_allowed is effected in subtypes to indicate in concrete terms when it is True, usually related to Void attribute values.

Assumed_value

When archetypes are defined to have optional parts, an ability to define ‘assumed’ values is useful. For example, an archetype for the concept ‘blood pressure measurement’ might contain an optional protocol section describing the patient position, with choices ‘lying’, ‘sitting’ and ‘standing’. Since the section is optional, data could be created according to the archetype which does not contain the protocol section. However, a blood pressure cannot be taken without the patient in some position, so clearly there could be an implied value for patient position. Amongst clinicians, basic assumptions are nearly always made for such things: in general practice, the position could always safely be assumed to be “sitting” if not otherwise stated; in the hospital setting, “lying” would be the normal assumption. The assumed values feature of archetypes allows such assumptions to be explicitly stated so that all users/systems know what value to assume when optional items are not included in the data. Assumed values are definable at the leaf level only, which appears to be adequate for all purposes described to date; accordingly, they appear in descendants of C_PRIMITIVE and also C_DOMAIN_TYPE.

The notion of assumed values is distinct from that of ‘default values’. The latter is a local requirement, and as such is stated in templates; default values do appear in data, while assumed values don’t.

Valid_value

The valid_value function tests a reference model object for conformance to the archetype. It is designed for recursive implementation in which a call to the function at the top of the archetype definition would cause a cascade of calls down the tree. This function is the key function of an ‘archetype-enabled kernel’ component that can perform runtime data validation based on an archetype definition.

Default_value

This function is used to generate a reasonable default value of the reference object being constrained by a given node. This allows archteype-based software to build a ‘prototype’ object from an archetype which can serve as the initial version of the object being constrained, assuming it is being created new by user activity (e.g. via a GUI application). Implementation of this function will usually involve use of reflection libraries or similar.

4.2.3.2 Complex Objects (C_COMPLEX_OBJECT)

Along with C_ATTRIBUTE, C_COMPLEX_OBJECT is the key structuring type of the constraint_model package, and consists of attributes of type C_ATTRIBUTE, which are constraints on the attributes (i.e. any property, including relationships) of the reference model type. Accordingly, each C_ATTRIBUTE records the name of the constrained attribute (in rm_attr_name), the existence and cardinality expressed by the constraint (depending on whether the attribute it constrains is a multiple or single relationship), and the constraint on the object to which this C_ATTRIBUTE refers via its children attribute (according to its reference model) in the form of further C_OBJECTs.

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4.2.3.3 Primitive Types

Constraints on primitive types are defined by the classes inheriting from C_PRIMITIVE, namely C_STRING, C_INTEGER and so on. These types do not inherit from ARCHETYPE_CONSTRAINT, but rather are related by association, in order to allow them to have the simplest possible definitions, independent even from the rest of ADL, in the hope of acceptance in heath standardisation organisations. Technically, avoiding inheritance from ARCHETYPE_CONSTRAINT / C_PRIMITIVE_OBJECT into these base types (in other words, coalescing the classes C_PRIMITIVE_OBJECT and C_PRIMITIVE) does not pose a problem, but could be effected at a later date if desired.

4.2.3.4 Domain-specific Extensions (C_DOMAIN_TYPE)

The main part of the archetype constraint model allows any type in a reference model to be archetyped - i.e. constrained - in a standard way, which is to say, by a regular cascade of C_COMPLEX_OBJECT / C_ATTRIBUTE / C_PRIMITIVE_OBJECT objects. This generally works well, especially for ‘outer’ container types in models. However, it occurs reasonably often that lower level logical ‘leaf’ types need special constraint semantics that are not conveniently achieved with the standard aproach. To enable such classes to be integrated into the generic constraint model, the class C_DOMAIN_TYPE is included. This enables the creation of specific “C_” classes, inheriting from C_DOMAIN_TYPE, which represent custom semantics for particular reference model types. For example, a class called C_QUANTITY might be created which has different constraint semantics from the default effect of a C_COMPLEX_OBJECT / C_ATTRIBUTE cascade representing such constraints in the generic way (i.e. systematically based on the reference model). An example of domain-specific extension classes is shown in Domain-specific Extension Example on page 53 .

4.2.3.5 Reference Objects (C_REFERENCE_OBJECT)

The subtypes of C_REFERENCE_OBJECT, namely, ARCHETYPE_SLOT, ARCHETYPE_INTERNAL_REF and CONSTRAINT_REF are used to express, respectively, a ‘slot’ where further archetypes can be used to continue describing constraints; a reference to a part of the current archetype that expresses exactly the same constraints needed at another point; and a reference to a constraint on a constraint defined in the archetype ontology, which in turn points to an external knowledge resource, such as a terminology.

A CONSTRAINT_REF is really a proxy for a set of constraints on an object that would normally occur at a particular point in the archetype as a C_COMPLEX_OBJECT, but where the actual definition of the constraints is outside the archetype definition proper, and is instead expressed in the binding of the constraint reference (e.g. ‘ac0004’) to a query or expression into an external service (e.g. a terminology service). The result of the query could be something like:

a set of allowed CODED_TERMs e.g. the types of hepatitis
an INTERVAL<QUANTITY> forming a reference range
a set of units or properties or other numerical item

See the ADL specification for a fuller explanation, under the heading Placeholder constraints in the cADL section.

4.2.4 Assertions

The C_ATTRIBUTE and subtypes of C_OBJECT enable constraints to be expressed in a structural fashion such that any constraint concerning a single attribute may be expressed, including recursively. In addition to this, any instance of a C_COMPLEX_OBJECT may include one or more invariants. Invariants are statements in a form of predicate logic, which can also be used to state constraints on parts of an object. They are not needed to constrain single attributes (since this can be done with an appopriate C_ATTRIBUTE), but are necessary for constraints referring to more than one attribute, such as a con

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straint that ‘systolic pressure should be >= diastolic pressure’ in a blood pressure measurement archetype. Invariants are expressed using a syntax derived from the OMG’s OCL syntax (adapted for use with objects rather than classes).

Assertions are also used in ARCHETYPE_SLOTs, in order to express the ‘included’ and ‘excluded’ archetypes for the slot. In this case, each assertion is an expression that refers to parts of other archetypes, such as its identifier (e.g. ‘include archetypes with short_concept_name matching xxxx’). Assertions are modelled here as a generic expression tree of unary prefix and binary infix operators. Examples of archetype slots in ADL syntax are given in the openEHR ADL document.

4.3 Class Definitions

4.3.1 ARCHETYPE_CONSTRAINT Class

CLASS	ARCHETYPE_CONSTRAINT (abstract)
Purpose	Archetype equivalent to LOCATABLE class in openEHR Common reference model. Defines common constraints for any inheritor of LOCATABLE in any reference model.
Abstract	Signature	Meaning
	is_subset_of (other: ARCHETYPE_CONSTRAINT): Boolean require other /= Void	True if constraints represented by other are narrower than this node. Note: not easily evaluatable for CONSTRAINT_REF nodes.
	is_valid: Boolean	True if this node (and all its sub-nodes) is a valid archetype node for its type. This function should be implemented by each subtype to perform semantic validation of itself, and then call the is_valid function in any subparts, and generate the result appropriately.
Functions	Signature	Meaning
	path: String	Path of this node relative to root of archetype.
	has_path (a_path: String): Boolean require a_path /= Void	True if the relative path a_path exists at this node.
Invariant	path_exists: path /= Void

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4.3.2 C_ATTRIBUTE Class

CLASS	C_ATTRIBUTE(abstract)
Purpose	Abstract model of constraint on any kind of attribute node.
Attributes	Signature	Meaning
1..1	rm_attribute_name: String	Reference model attribute within the enclosing type represented by a C_OBJECT.
1..1	existence: Interval<Integer>	Constraint on every attribute, regardless of whether it is singular or of a container type, which indicates whether its target object exists or not (i.e. is mandatory or not).
0..1	children: List<C_OBJECT>	Child C_OBJECT nodes. Each such node represents a constraint on the type of this attribute in its reference model. Multiples occur both for multiple items in the case of container attributes, and alternatives in the case of singular attributes.
Invariant	Rm_attribute_name_valid: rm_attribute_name /= Void and then not rm_attribute_name.is_empty Existence_set: existence /= Void and then (existence.lower >= 0 and existence.upper <= 1) Children_validity: any_allowed xor children /= Void

4.3.3 C_SINGLE_ATTRIBUTE Class

CLASS	C_SINGLE_ATTRIBUTE
Purpose	Concrete model of constraint on a single-valued attribute node. The meaning of the inherited children attribute is that they are alternatives.
Functions	Signature	Meaning
	alternatives: List<C_OBJECT>	List of alternative constraints for the single child of this attribute within the data.
Invariant	Alternatives_exists: alternatives /= Void

4.3.4 C_MULTIPLE_ATTRIBUTE Class

CLASS	C_MULTIPLE_ATTRIBUTE
Purpose	Abstract model of constraint on any kind of attribute node.
Attributes	Signature	Meaning

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CLASS	C_MULTIPLE_ATTRIBUTE
1..1	cardinality: CARDINALITY	Cardinality of this attribute constraint, if it constraints a container attribute.
Functions	Signature	Meaning
	members: List<C_OBJECT>	List of constraints representing members of the container value of this attribute within the data. Semantics of the uniqueness and ordering of items in the container are given by the cardinality.
Invariant	Cardinality_validity: cardinality /= Void Members_valid: members /= Void and then members.for_all(co: C_OBJECT \| co.occurrences.upper <= 1)

4.3.5 CARDINALITY Class

© 2004-2007 The openEHR Foundation. email: info@openEHR.org web: http://www.openEHR.org
CLASS	CARDINALITY
Purpose	Express constraints on the cardinality of container objects which are the values of multiply-valued attributes, including uniqueness and ordering, providing the means to state that a container acts like a logical list, set or bag. The cardinality cannot contradict the cardinality of the corresponding attribute within the relevant reference model.
Attributes	Signature	Meaning
1..1	is_ordered: Boolean	True if the members of the container attribute to which this cardinality refers are ordered.
1..1	is_unique: Boolean	True if the members of the container attribute to which this cardinality refers are unique.
1..1	interval: Interval<Integer>	The interval of this cardinality.
Functions	Signature	Meaning
	is_bag: Boolean ensure Result = not is_ordered and not is_unique	True if the semantics of this cardinality represent a set, i.e. unordered, unique membership.
	is_list: Boolean ensure Result = is_ordered and not is_unique	True if the semantics of this cardinality represent a list, i.e. ordered, non-unique membership.

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CLASS	CARDINALITY
	is_set Boolean ensure Result = not is_ordered and is_unique	True if the semantics of this cardinality represent a bag, i.e. unordered, non-unique membership.
Invariant	Validity: not interval.lower_unbounded

4.3.6 C_OBJECT Class

CLASS	C_OBJECT (abstract)
Purpose	Abstract model of constraint on any kind of object node.
Attributes	Signature	Meaning
1..1	rm_type_name: String	Reference model type that this node corresponds to.
1..1	occurrences: Interval<Integer>	Occurrences of this object node in the data, under the owning attribute. Upper limit can only be greater than 1 if owning attribute has a cardinality of more than 1).
1..1	node_id: String	Semantic id of this node, used to differentiate sibling nodes of the same type. [Previously called ‘meaning’]. Each node_id must be defined in the archetype ontology as a term code.
0..1	parent: C_ATTRIBUTE	C_ATTRIBUTE that owns this C_OBJECT.
Invariant	rm_type_name_valid: rm_type_name /= Void and then not rm_type_name.is_empty node_id_valid: node_id /= Void and then not node_id.is_empty Occurrences_validity: occurrences /= Void and then (parent /= Void implies (not parent.is_multiple implies occurrences.upper <= 1))

4.3.7 C_DEFINED_OBJECT Class

CLASS	C_DEFINED_OBJECT (abstract)
Purpose	Abstract parent type of C_OBJECT subtypes that are defined by value, i.e. whose definitions are actually in the archetype rather than being by reference.
Inherit	C_OBJECT
Abstract	Signature	Meaning

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CLASS	C_DEFINED_OBJECT (abstract)
	default_value: like assumed_value Generate a default value from this constraint object
	valid_value (a_value: like assumed_value): Boolean require a_value /= Void True if a_value is valid with respect to constraint expressed in concrete instance of this type.
	any_allowed: Boolean True if any value (i.e. instance) of the reference model type would be allowed. Redefined in descedants.
Attributes	Signature Meaning
0..1	assumed_value: Any Value to be assumed if none sent in data
Functions	Signature Meaning
	has_assumed_value: Boolean True if there is an assumed value Assumed_value_valid: has_assumed_value implies valid_value(assumed_value)
Invariant

4.3.8 C_COMPLEX_OBJECT Class

CLASS	C_COMPLEX_OBJECT
Purpose	Constraint on complex objects, i.e. any object that consists of other object constraints.
Inherit	C_DEFINED_OBJECT
Functions	Signature	Meaning
(effected)	any_allowed: Boolean ensure Result = attributes.is_empty	True if any value of the reference model type being constrained is allowed.
Attributes	Signature	Meaning
0..1	attributes: Set<C_ATTRIBUTE>	List of constraints on attributes of the reference model type represented by this object.
Invariant	attributes_valid: any_allowed xor (attributes /= Void and not attributes.is_empty)

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4.3.9 C_PRIMITIVE_OBJECT Class

CLASS	C_PRIMITIVE_OBJECT
Purpose	Constraint on a primitive type.
Inherit	C_DEFINED_OBJECT
Functions	Signature	Meaning
(effected)	any_allowed: Boolean ensure Result = (item = Void)	True if any value of the type being constrained in item is allowed.
Attributes	Signature	Meaning
0..1	item: C_PRIMITIVE	Object actually defining the constraint.
Invariant	item_exists: any_allowed xor item /= Void

4.3.10 C_DOMAIN_TYPE Class

CLASS	C_DOMAIN_TYPE (abstract)
Purpose	Abstract parent type of domain-specific constrainer types, to be defined in external packages.
Inherit	C_DEFINED_OBJECT
Abstract	Signature	Meaning
	standard_equivalent: C_COMPLEX_OBJECT	Standard (i.e. C_OBJECT) form of constraint.
Invariant

4.3.11 C_REFERENCE_OBJECT Class

CLASS	C_REFERENCE_OBJECT (abstract)
Purpose	Abstract parent type of C_OBJECT subtypes that are defined by reference.
Inherit	C_OBJECT
Abstract	Signature	Meaning
Invariant

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4.3.12 ARCHETYPE_SLOT Class

CLASS	ARCHETYPE_SLOT
Purpose	Constraint describing a ‘slot’ where another archetype can occur.
Inherit	C_REFERENCE_OBJECT
Attributes	Signature	Meaning
0..1	includes: Set <ASSERTION>	List of constraints defining other archetypes that could be included at this point.
0..1	excludes: Set<ASSERTION>	List of constraints defining other archetypes that cannot be included at this point.
Invariant	includes_valid: includes /= Void implies not includes.is_empty excludes_valid: excludes /= Void implies not excludes.is_empty validity: any_allowed xor (includes /= Void or excludes /= Void)

4.3.13 ARCHETYPE_INTERNAL_REF Class

CLASS	ARCHETYPE_INTERNAL_REF
Purpose	A constraint defined by proxy, using a reference to an object constraint defined elsewhere in the same archetype. Note that since this object refers to another node, there are two objects with available occurrences values. The local occurrences value on an ARCHETYPE_INTERNAL_REF should always be used; when setting this from a serialised form, if no occurrences is mentioned, the target occurrences should be used (not the standard default of {1..1}); otherwise the locally specified occurrences should be used as normal. When serialising out, if the occurrences is the same as that of the target, it can be left out.
Inherit	C_REFERENCE_OBJECT
Attributes	Signature	Meaning
1..1	target_path: String	Reference to an object node using archetype path notation.
Invariant	Consistency: not any_allowed target_path_valid: target_path /= Void and then not target_path.is_empty --and then ultimate_root.has_path(target_path)

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4.3.14 CONSTRAINT_REF Class

CLASS	CONSTRAINT_REF
Purpose	Reference to a constraint described in the same archetype, but outside the main constraint structure. This is used to refer to constraints expressed in terms of external resources, such as constraints on terminology value sets.
Inherit	C_REFERENCE_OBJECT
Attributes	Signature	Meaning
1..1	reference: String	Reference to a constraint in the archetype local ontology.
Invariant	Consistency: not any_allowed reference_valid: reference /= Void

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The Assertion Package

5.1 Overview

Assertions are expressed in archetypes in typed first-order predicate logic (FOL). They are used in two places: to express archetype slot constraints, and to express invariants in complex object constraints. In both of these places, their role is to constrain something inside the archetype. Constraints on external resources such as terminologies are expressed in the constraint binding part of the archetype ontology, described in section 7 on page 49. The assertion package is illustrated below in FIG URE 7.

assertion

FIGURE 7 The openehr.am.archetype.assertion package

5.2 Semantics

The concrete syntax of assertion statements in archetypes is designed to be compatible with the OMG Object Constraint Language (OCL) [10]. Archetype assertions are essentially statements which con tain the following elements:

variables, which are attribute names, or ADL paths terminating in attribute names (i.e. equivalent of referencing class feature in a programming language);
manifest constants of any primitive type, plus date/time types
arithmetic operators: +, *, -, /, ^ (exponent), % (modulo division)
relational operators: >, <, >=, <=, =, !=, matches
boolean operators: not, and, or, xor
quantifiers applied to container variables: for_all, exists

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The written syntax of assertions is defined in the openEHR ADL document. The package described here is currently designed to allow the representation of a general-purpose binary expression tree, as would be generated by a parser. This may be replaced in the future by a more specific model, if needed.

This relatively simple model of expressions is sufficiently powerful for representing FOL expressions on archetype structures, although it could clearly be more heavily subtyped.

5.3 Class Descriptions

5.3.1 ASSERTION Class

CLASS	ASSERTION
Purpose	Structural model of a typed first order predicate logic assertion, in the form of an expression tree, including optional variable definitions.
Attributes	Signature	Meaning
0..1	tag: String	Expression tag, used for differentiating multiple assertions.
1..1	expression: EXPR_ITEM	Root of expression tree.
0..1	string_expression: String	String form of expression, in case an expression evaluator taking String expressions is used for evaluation.
0..1	variables: List<ASSERTION_VARIABLE>	Definitions of variables used in the assertion expression.
Invariant	Tag_valid: tag /= Void implies not tag.is_empty Expression_valid: expression /= Void and then expres-sion.type.is_equal(“BOOLEAN”)

5.3.2 EXPR_ITEM Class

CLASS	EXPR_ITEM (abstract)
Purpose	Abstract parent of all expression tree items.
Attributes	Signature	Meaning
1..1	type: String	Type name of this item in the mathematical sense. For leaf nodes, must be the name of a primitive type, or else a reference model type. The type for any relational or boolean operator will be “Boolean”, while the type for any arithmetic operator, will be “Real” or “Integer”.

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Type_valid: type /= Void and then not type.is_empty

5.3.3 EXPR_LEAF Class

CLASS	EXPR_LEAF
Purpose	Expression tree leaf item. This can represent one of: • a manifest constant of any primitive type (Integer, Real, Boolean, String, Character, Date, Time, Date_time, Duration), or (in future) of any complex reference model type, e.g. a DV_CODED_TEXT; • a path referring to a value in the archetype (paths with a leading ‘/’ are in the definition section; paths with no leading ‘/’ are in the outer part of the archetype, e.g. “archetype_id/value” refers to the String value of the archetype_id attribute of the enclosing archetype; • a constraint, expressed in the form of concrete subtype of C_OBJECT; most often this will be a C_PRIMITIVE_OBJECT.
Inherit	EXPR_ITEM
Attributes	Signature	Meaning
1..1	item: ANY	The value referred to; a manifest constant, an attribute path (in the form of a String), or for the right-hand side of a ‘matches’ node, a constraint, often a C_PRIMITIVE_OBJECT. [Future: paths including function names as well, even if not constrained in the archetype - as long as they are in the reference model].
1..1	reference_type: String	Type of reference: “constant”, “attribute”, “function”, “constraint”. The first three are used to indicate the referencing mechanism for an operand. The last is used to indicate a constraint operand, as happens in the case of the right-hand operand of the ‘matches’ operator.
Invariant	Item_valid: item /= Void Reference_type_valid: reference_type /= Void

5.3.4 EXPR_OPERATOR Class

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CLASS	EXPR_OPERATOR (abstract)
Inherit	EXPR_ITEM
Attributes	Signature	Meaning
1..1	operator: OPERATOR_KIND	Code of operator.
1..1	precedence_overridden: Boolean	True if the natural precedence of operators is overridden in the expression represented by this node of the expression tree. If True, parentheses should be introduced around the totality of the syntax expression corresponding to this operator node and its operands.
Invariant

5.3.5 EXPR_UNARY_OPERATOR Class

CLASS	EXPR_UNARY_OPERATOR
Purpose	Unary operator expression node.
Inherit	EXPR_OPERATOR
Attributes	Signature	Meaning
1..1	operand: EXPR_ITEM	Operand node.
Invariant	operand_valid: operand /= Void

5.3.6 EXPR_BINARY_OPERATOR Class

CLASS	EXPR_BINARY_OPERATOR
Purpose	Binary operator expression node.
Inherit	EXPR_OPERATOR
Attributes	Signature	Meaning
1..1	left_operand: EXPR_ITEM	Left operand node.
1..1	right_operand: EXPR_ITEM	Right operand node.
Invariant	left_operand_valid: operand /= Void right_operand_valid: operand /= Void

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5.3.7 ASSERTION_VARIABLE Class

CLASS	ASSERTION_VARIABLE
Purpose	Definition of a named variable used in an assertion expression. Note: the definition of named variables may change; still under development in ADL2.
Attributes	Signature	Meaning
1..1	name: String	Name of variable.
1..1	definition: String	Formal definition of the variable. (see ADL2 specification; still under development).
Invariant	Name_valid: name /= Void and then not name.is_empty Definition_valid: definition /= Void and then not definition.is_empty

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5.3.8 OPERATOR_KIND Class

© 2004-2007 The openEHR Foundation. email: info@openEHR.org web: http://www.openEHR.org
CLASS	OPERATOR_KIND
Purpose	Enumeration type for operator types in assertion expressions
Use	Use as the type of operators in the Assertion package, or for related uses.
Constants	Signature	Meaning
	op_eq: Integer = 2001	Equals operator (‘=’ or ‘==’)
	op_ne: Integer = 2002	Not equals operator (‘!=’ or ‘/=’ or ‘<>’)
	op_le: Integer = 2003	Less-than or equals operator (‘<=’)
	op_lt: Integer = 2004	Less-than operator (‘<’)
	op_ge: Integer = 2005	Greater-than or equals operator (‘>=’)
	op_gt: Integer = 2006	Greater-than operator (‘>’)
	op_matches: Integer = 2007	Matches operator (‘matches’ or ‘is_in’)

	op_not: Integer = 2010	Not logical operator
	op_and: Integer = 2011	And logical operator
	op_or: Integer = 2012	Or logical operator
	op_xor: Integer = 2013	Xor logical operator
	op_implies: Integer = 2014	Implies logical operator
	op_for_all: Integer = 2015	For-all quantifier operator
	op_exists: Integer = 2016	Exists quantifier operator

	op_plus: Integer = 2020	Plus operator (‘+’)
	op_minus: Integer = 2021	Minus operator (‘-’)
	op_multiply: Integer = 2022	Multiply operator (‘*’)
	op_divide: Integer = 2023	Divide operator (‘/’)

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CLASS	OPERATOR_KIND
	op_exp: Integer = 2024	Exponent operator (‘^’)
Attributes	Signature	Meaning
	value: Integer	Actual value of this instance
Functions	Signature	Meaning
	valid_operator (an_op: Integer): Boolean ensure an_op >= op_eq and an_op <= op_exp	Function to test operator values.
Invariant	Validity: valid_operator(value)

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Archetype Object Model The Primitive Package Rev 2.0.1

The Primitive Package

6.1 Overview

Ultimately any archetype definition will devolve down to leaf node constraints on instances of primi tive types. The primitive package, illustrated in FIGURE 8, defines the semantics of constraint on such types.

C_PRIMITIVE_OBJECT (am.archetype.constraint_model)

1

item

primitive

C_PRIMITIVE

default_value: ANY assumed_value: ANY has_assumed_value: Boolean valid_value(a_value:ANY): Boolean

C_INTEGER

C_REAL C_BOOLEAN C_STRING

list[0..1]: Set<Integer>

list[0..1]: Set<Real> Boolean

true_valid[1]: pattern[0..1]: String

range[0..1]: false_valid[1]:

range[0..1]:

list[0..1]: Set<String>

Interval<Real> Boolean

Interval<Integer>

list_open[0..1]:

assumed_value: Integer

assumed_value: Real assumed_value[0..1]

Boolean

assumed_value

: Boolean [0..1]: String

C_DURATION C_DATE_TIME C_DATE C_TIME

years_allowedmonth_validity[0..1]:

month_validity[0..1]:

minute_validity[0..1]:

[0..1]: Boolean day_validity[0..1]:

VALIDITY_KIND VALIDITY_KIND VALIDITY_KIND months_allowed day_validity[0..1]:

second_validity[0..1]:

[0..1]: Boolean timezone_validity[0..1]:

VALIDITY_KIND VALIDITY_KIND VALIDITY_KIND weeks_allowed hour_validity[0..1]:

millisecond_validity

[0..1]: Boolean range[0..1]: Interval<Date>

VALIDITY_KIND VALIDITY_KIND [0..1]: VALIDITY_KIND

days_allowed assumed_value[0..1]: Date

minute_validity[0..1]:

timezone_validity[0..1]:

[0..1]: Boolean range[0..1]:

VALIDITY_KIND VALIDITY_KIND hours_allowed second_validity[0..1]:

[0..1]: Boolean assumed_value[0..1]:

VALIDITY_KIND Interval<Time> minutes_allowed millisecond_validity[0..1]:

[0..1]: Boolean timezone_validity[0..1]:

VALIDITY_KIND Time seconds_allowed

[0..1]: Boolean range[0..1]:

VALIDITY_KIND fractional_seconds_

allowed assumed_value[0..1]:

Interval<Date_Time>

[0..1]: Boolean Date_Time

range[0..1]: Interval<Duration>

assumed_value

[0..1]: Duration

FIGURE 8 The openehr.am.archetype.primitive Package

Most of the types provide at least two alternative ways to represent the constraint; for example the C_DATE type allows the constraint to be expressed in the form of a pattern (defined in the ADL speci

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fication) or an Interval<Date>. Note that the interval form of dates is probably only useful for historical date checking (e.g. the date of an antique or a particular batch of vaccine), rather than constraints on future date/times.

6.2 Class Descriptions

6.2.1 C_PRIMITIVE Class

CLASS	C_PRIMITIVE (abstract)
Purpose	Abstract supertype of all prmitive types.
Abstract	Signature	Meaning
1..1	default_value: ANY	Generate a default value from this constraint object
1..1	has_assumed_value: Boolean	True if there is an assumed value
1..1	assumed_value: like default_value	Value to be assumed if none sent in data
	valid_value (a_value: like default_value): Boolean require a_value /= Void	True if a_value is valid with respect to constraint expressed in concrete instance of this type.
Invariant	Assumed_value_valid: has_assumed_value implies valid_value(assumed_value)

6.2.2 C_BOOLEAN Class

CLASS	C_BOOLEAN
Purpose	Constraint on instances of Boolean.
Use	Both attributes cannot be set to False, since this would mean that the Boolean value being constrained cannot be True or False.
Inherit	C_PRIMITIVE
Attributes	Signature	Meaning
1..1	true_valid: Boolean	True if the value True is allowed
1..1	false_valid: Boolean	True if the value False is allowed
1..1 (redefined)	assumed_value: Boolean	The value to assume if this item is not included in data, due to being part of an optional structure.

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Binary_consistency: true_valid or false_valid Default_value_consistency: default_value.value and true_valid or else not default_value.value and false_valid

6.2.3 C_STRING Class

CLASS	C_STRING
Purpose	Constraint on instances of STRING.
Inherit	C_PRIMITIVE
Attributes	Signature	Meaning
0..1 (cond)	pattern: String	Regular expression pattern for proposed instances of String to match.
0..1 (cond)	list: Set<String>	Set of Strings specifying constraint
1..1	list_open: Boolean	True if the list is being used to specify the constraint but is not considered exhaustive.
1..1 (redefined)	assumed_value: String	The value to assume if this item is not included in data, due to being part of an optional structure.
Invariant	Consistency: pattern /= Void xor list /= Void pattern_exists: pattern /= Void implies not pattern.is_empty

6.2.4 C_INTEGER Class

CLASS	C_INTEGER
Purpose	Constraint on instances of Integer.
Inherit	C_PRIMITIVE
Attributes	Signature	Meaning
0..1 (cond)	list: Set<Integer>	Set of Integers specifying constraint
0..1 (cond)	range: Interval<Integer>	Range of Integers specifying constraint

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CLASS	C_INTEGER
1..1 (redefined)	assumed_value: Integer	The value to assume if this item is not included in data, due to being part of an optional structure.
Invariant	Consistency: list /= Void xor range /= Void

6.2.5 C_REAL Class

CLASS	C_REAL
Purpose	Constraint on instances of Real.
Inherit	C_PRIMITIVE
Attributes	Signature	Meaning
0..1 (cond)	list: Set<Real>	Set of Reals specifying constraint
0..1 (cond)	range: Interval<Real>	Range of Real specifying constraint
1..1 (redefined)	assumed_value: Real	The value to assume if this item is not included in data, due to being part of an optional structure.
Invariant	Consistency: list /= Void xor range /= Void

6.2.6 C_DATE Class

CLASS	C_DATE
Purpose	ISO 8601-compatible constraint on instances of Date in the form either of a set of validity values, or an actual date range. There is no validity flag for ‘year’, since it must always be by definition mandatory in order to have a sensible date at all. Syntax expressions of instances of this class include “YYYY-??-??” (date with optional month and day).
Use	Date ranges are probably only useful for historical dates.
Inherit	C_PRIMITIVE
Attributes	Signature	Meaning
0..1 (cond)	month_validity: VALIDITY_KIND	Validity of month in constrained date.

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CLASS	C_DATE
0..1 (cond)	day_validity: VALIDITY_KIND Validity of day in constrained date.
0..1 (cond)	timezone_validity: VALIDITY_KIND Validity of timezone in constrained date.
0..1 (cond)	range: Interval<Date> Interval of Dates specifying constraint
1..1 (redefined)	assumed_value: Date The value to assume if this item is not included in data, due to being part of an optional structure.
Functions	Signature Meaning
1..1	validity_is_range: Boolean True if validity is in the form of a range; useful for developers to check which kind of constraint has been set. Month_validity_optional: month_validity = {VALIDITY_KIND}.optional implies (day_validity = {VALIDITY_KIND}.optional or day_validity = {VALIDITY_KIND}.disallowed) Month_validity_disallowed: month_validity = {VALIDITY_KIND}.disallowed implies day_validity = {VALIDITY_KIND}.disallowed Validity_is_range: validity_is_range = (range /= Void)
Invariant

6.2.7 C_TIME Class

© 2004-2007 The openEHR Foundation. email: info@openEHR.org web: http://www.openEHR.org
CLASS	C_TIME
Purpose	ISO 8601-compatible constraint on instances of Time. There is no validity flag for ‘hour’, since it must always be by definition mandatory in order to have a sensible time at all. Syntax expressions of instances of this class include “HH:??:xx” (time with optional minutes and seconds not allowed).
Inherit	C_PRIMITIVE
Attributes	Signature	Meaning
0..1 (cond)	minute_validity: VALIDITY_KIND	Validity of minute in constrained time.
0..1 (cond)	second_validity: VALIDITY_KIND	Validity of second in constrained time.
0..1 (cond)	millisecond_validity: VALIDITY_KIND	Validity of millisecond in constrained time.

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CLASS	C_TIME
0..1 (cond)	timezone_validity: VALIDITY_KIND Validity of timezone in constrained date.
0..1 (cond)	range: Interval<Time> Interval of Times specifying constraint
1..1 (redefined)	assumed_value: Time The value to assume if this item is not included in data, due to being part of an optional structure.
Functions	Signature Meaning validity_is_range: Boolean True if validity is in the form of a range; useful for developers to check which kind of constraint has been set. Minute_validity_optional: minute_validity = {VALIDITY_KIND}.optional implies (second_validity = {VALIDITY_KIND}.optional or second_validity = {VALIDITY_KIND}.disallowed) Minute_validity_disallowed: minute_validity = {VALIDITY_KIND}.disallowed implies second_validity = {VALIDITY_KIND}.disallowed Second_validity_optional: second_validity = {VALIDITY_KIND}.optional implies (millisecond_validity = {VALIDITY_KIND}.optional or millisecond_validity = {VALIDITY_KIND}.disallowed) Second_validity_disallowed: second_validity = {VALIDITY_KIND}.disallowed implies millisecond_validity = {VALIDITY_KIND}.disallowed Validity_is_range: validity_is_range = (range /= Void)
1..1
Invariant

6.2.8 C_DATE_TIME Class

© 2004-2007 The openEHR Foundation. email: info@openEHR.org web: http://www.openEHR.org
CLASS	C_DATE_TIME
Purpose	ISO 8601-compatible constraint on instances of Date_Time. There is no validity flag for ‘year’, since it must always be by definition mandatory in order to have a sensible date/time at all. Syntax expressions of instances of this class include “YYYY-MM-DDT??:??:??” (date/time with optional time) and “YYYY-MMDDTHH:MM:xx” (date/time, seconds not allowed).
Inherit	C_PRIMITIVE
Attributes	Signature	Meaning
0..1 (cond)	month_validity: VALIDITY_KIND	Validity of month in constrained date.
0..1 (cond)	day_validity: VALIDITY_KIND	Validity of day in constrained date.

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CLASS	C_DATE_TIME
0..1 (cond)	hour_validity: VALIDITY_KIND	Validity of hour in constrained time.
0..1 (cond)	minute_validity: VALIDITY_KIND	Validity of minute in constrained time.
0..1 (cond)	second_validity: VALIDITY_KIND	Validity of second in constrained time.
0..1 (cond)	millisecond_validity: VALIDITY_KIND	Validity of millisecond in constrained time.
0..1 (cond)	timezone_validity: VALIDITY_KIND	Validity of timezone in constrained date.
0..1 (cond)	range: Interval<Date_Time>	Range of Date_times specifying constraint
1..1 (redefined)	assumed_value: Date_Time	The value to assume if this item is not included in data, due to being part of an optional structure.
Functions	Signature validity_is_range: Boolean	Meaning True if validity is in the form of a range; useful for developers to check which kind of constraint has been set.
1..1	Signature validity_is_range: Boolean

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Month_validity_optional: month_validity = {VALIDITY_KIND}.optional implies (day_validity = {VALIDITY_KIND}.optional or day_validity = {VALIDITY_KIND}.disallowed) Month_validity_disallowed: month_validity = {VALIDITY_KIND}.disallowed implies day_validity = {VALIDITY_KIND}.disallowed Day_validity_optional: day_validity = {VALIDITY_KIND}.optional implies (hour_validity = {VALIDITY_KIND}.optional or hour_validity = {VALIDITY_KIND}.disallowed) Day_validity_disallowed: day_validity = {VALIDITY_KIND}.disallowed implies hour_validity = {VALIDITY_KIND}.disallowed Hour_validity_optional: hour_validity = {VALIDITY_KIND}.optional implies (minute_validity = {VALIDITY_KIND}.optional or minute_validity = {VALIDITY_KIND}.disallowed) Hour_validity_disallowed: hour_validity = {VALIDITY_KIND}.disallowed implies minute_validity = {VALIDITY_KIND}.disallowed Minute_validity_optional: minute_validity = {VALIDITY_KIND}.optional implies (second_validity = {VALIDITY_KIND}.optional or second_validity = {VALIDITY_KIND}.disallowed) Minute_validity_disallowed: minute_validity = {VALIDITY_KIND}.disallowed implies second_validity = {VALIDITY_KIND}.disallowed Second_validity_optional: second_validity = {VALIDITY_KIND}.optional implies (millisecond_validity = {VALIDITY_KIND}.optional or millisecond_validity = {VALIDITY_KIND}.disallowed) Second_validity_disallowed: second_validity = {VALIDITY_KIND}.disallowed implies millisecond_validity = {VALIDITY_KIND}.disallowed Validity_is_range: validity_is_range = (range /= Void)

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6.2.9 C_DURATION Class

CLASS	C_DURATION
Purpose	ISO 8601-compatible constraint on instances of Duration. In ISO 8601 terms, constraints might are of the form “PWD” (weeks and/or days), “PDTHMS” (days, hours, minutes, seconds) and so on. In official ISO 8601:2004, the ‘W’ (week) designator cannot be mixed in; allowing it is an openEHR-wide exception.
Inherit	C_PRIMITIVE
Attributes	Signature	Meaning
0..1	years_allowed: Boolean	True if years are allowed in the constrained Duration.
0..1	months_allowed: Boolean	True if months are allowed in the constrained Duration.
0..1	weeks_allowed: Boolean	True if weeks are allowed in the constrained Duration.
0..1	days_allowed: Boolean	True if days are allowed in the constrained Duration.
0..1	hours_allowed: Boolean	True if hours are allowed in the constrained Duration.
0..1	minutes_allowed: Boolean	True if minutes are allowed in the constrained Duration.
0..1	seconds_allowed: Boolean	True if seconds are allowed in the constrained Duration.
0..1	fractional_seconds_allowed: Boolean	True if fractional seconds are allowed in the constrained Duration.
1..1	range: Interval<Duration>	Range of Durations specifying constraint
1..1 (redefined)	assumed_value: Duration	The value to assume if this item is not included in data, due to being part of an optional structure.
Invariant	Range_valid: range /= Void or else (years_allowed or months_allowed or weeks_allowed or days_allowed or hours_allowed or minutes_allowed or seconds_allowed or fractional_seconds_allowed)

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Archetype Object Model Ontology Package Rev 2.0.1

Ontology Package

7.1 Overview

All linguistic and terminological entities in an archetype are represented in the ontology part of an archetype, whose semantics are given in the Ontology package, shown below.

FIGURE 9 openehr.am.archetype.ontology Package

An archetype ontology consists of the following things.

A list of terms defined local to the archetype. These are identified by ‘atNNNN’ codes, and perform the function of archetype node identifiers from which paths are created. There is one such list for each natural language in the archetype. A term ‘at0001’ defined in English as ‘blood group’ is an example.
A list of external constraint definitions, identified by ‘acNNNN’ codes, for constraints defined external to the archetype, and referenced using an instance of a CONSTRAINT_REF. There is one such list for each natural language in the archetype. A term ‘ac0001’ corresponding to ‘any term which is-a blood group’, which can be evaluated against some external terminology service.
Optionally, a set of one or more bindings of term definitions to term codes from external terminologies.
Optionally, a set of one or more bindings of the external constraint definitions to external resources such as terminlogies.

7.2 Semantics

Specialisation Depth

Any given archetype occurs at some point in a hierarchy of archetypes related by specialisation, where the depth is indicated by the specialisation_depth attribute. An archetype which is not a spe

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cialisation of another has a specialisation_depth of 0. Term and constraint codes introduced in the ontology of specialised archetypes (i.e. which did not exist in the ontology of the parent archetype) are defined in a strict way, using ‘.’ (period) markers. For example, an archetype of specialisation depth 2 will use term definition codes like the following:

‘at0.0.1’ - a new term introduced in this archetype, which is not a specialisation of any previous term in any of the parent archetypes;
‘at0001.0.1’ - a term which specialises the ‘at0001’ term from the top parent. An intervening ‘.0’ is required to show that the new term is at depth 2, not depth 1;
‘at0001.1.1’ - a term which specialises the term ‘at0001.1’ from the immediate parent, which itself specialises the term ‘at0001’ from the top parent.

This systematic definition of codes enables software to use the structure of the codes to more quickly and accurately make inferences about term definitions up and down specialisation hierarchies. Constraint codes on the other hand do not follow these rules, and exist in a flat code space instead.

Term and Constraint Definitions

Local term and constraint definitions are modelled as instances of the class ARCHETYPE_TERM, which is a code associated with a list of name/value pairs. For any term or constraint definition, this list must at least include the name/value pairs for the names “text” and “description”. It might also include such things as “provenance”, which would be used to indicate that a term was sourced from an external terminology. The attribute term_attribute_names in ARCHETYPE_ONTOLOGY provides a list of attribute names used in term and constraint definitions in the archetype, including “text” and “description”, as well as any others which are used in various places.

7.3 Class Descriptions

7.3.1 ARCHETYPE_ONTOLOGY Class

CLASS	ARCHETYPE_ONTOLOGY
Purpose	Local ontology of an archetype.
Attributes	Signature	Meaning
1..1	terminologies_available: Set<String>	List of terminologies to which term or constraint bindings exist in this terminology.
1..1	specialisation_depth: Integer	Specialisation depth of this archetype. Unspecialised archetypes have depth 0, with each additional level of specialisation adding 1 to the specialisation_depth.

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© 2004-2007 The openEHR Foundation. email: info@openEHR.org web: http://www.openEHR.org
CLASS	ARCHETYPE_ONTOLOGY
1..1	term_codes: List<String>	List of all term codes in the ontology. Most of these correspond to “at” codes in an ADL archetype, which are the node_ids on C_OBJECT descendants. There may be an extra one, if a different term is used as the overall archetype concept from that used as the node_id of the outermost C_OBJECTin the definition part.
1..1	constraint_codes: List<String>	List of all term codes in the ontology. These correspond to the “ac” codes in an ADL archetype, or equivalently, the CONSTRAINT_REF.reference values in the archetype definition.
1..1	term_attribute_names: List<String>	List of ‘attribute’ names in ontology terms, typically includes ‘text’, ‘description’, ‘provenance’ etc.
1..1	parent_archetype: ARCHETYPE	Archetype which owns this ontology.
Functions	Signature has_language(a_lang: String): Boolean	Meaning True if language ‘a_lang’ is present in archetype ontology.
	Signature has_language(a_lang: String): Boolean
	has_terminology(a_terminology _id: String): Boolean require has_terminology(a_terminology_ id)	True if terminology ‘a_terminology’ is present in archetype ontology.
	has_term_code(a_code: String): Boolean	True if term_codes has a_code.
	has_constraint_code(a_code: String): Boolean	True if constraint_codes has a_code.
	constraint_definition(a_lang, a_code: String): ARCHETYPE_TERM require has_language(a_lang) has_constraint_code(a_code)	Constraint definition for a code, in a specified language.

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CLASS	ARCHETYPE_ONTOLOGY
	term_binding (a_terminology_id, a_code: String): CODE_PHRASE require has_terminology(a_terminology_ id) has_term_code(a_code)	Binding of term corresponding to a_code in target external terminology a_terminology_id as a CODE_PHRASE.
	constraint_binding (a_terminology_id, a_code: String): String require has_terminology(a_terminology_ id) has_constraint_code(a_code)	Binding of constraint corresponding to a_code in target external terminology a_terminology_id, as a string, which is usually a formal query expression.
Invariant	terminologies_available_exists: terminologies_available /= void term_codes_exists: term_codes /= void constraint_codes_exists: constraint_codes /= void term_bindings_exists: term_bindings /= void constraint_bindings_exists: constraint_bindings /= void term_attribute_names_valid: term_attribute_names /= void and then term_attribute_names.has(“text”) and term_attribute_names.has(“description”) Parent_archetype_valid: parent_archetype /= Void and then parent_archetype.description = Current

7.3.2 ARCHETYPE_TERM Class

CLASS	ARCHETYPE_TERM
Purpose Attributes	Representation of any coded entity (term or constraint) in the archetype ontology. Signature Meaning
1..1	code: String Code of this term.
0..1	items: Hash <String, String> Hash of keys (“text”, “description” etc) and corresponding values.
Functions	Signature Meaning
1..1	keys: Set<String> List of all keys used in this term.
Invariant	code_valid: code /= void and then not code.is_empty keys_valid: keys /= Void

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A Domain-specific Extension Example

A.1 Overview

Domain-specific classes can be added to the archetype constraint model by inheriting from the class C_DOMAIN_TYPE. This section provides an example of how domain-specific constraint classes are added to the archetype model. Actual additions to the AOM for openEHR are documented in the openEHR Archetype Profile (oAP) specification.

A.2 Scientific/Clinical Computing Types

FIGURE 10 shows the general approach, used to add constraint classes for commonly used concepts in scientific and clinical computing, such as ‘ordinal’ (used heavily in medicine, particularly in pathology testing), ‘coded term’ (also heavily used in clinical computing) and ‘quantity’, a general scientific meansurement concept. The constraint types shown are C_ORDINAL, C_CODED_TEXT and C_QUANTITY which can optionally be used in archetypes to replace the default constraint semantics represented by the use of instances of C_OBJECT / C_ATTRIBUTE to constrain ordinals, coded terms and quantities. The following model is intended only as an example, and does not try to define any normative semantics of the particular constraint types shown.

C_DOMAIN_TYPE

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B Using Archetypes with Diverse Reference Models

B.1 Overview

The archetype model described in this document can be used with any reference model which is expressed in UML or a similar object-oriented formalism. It can also be used with E/R models. The following section describes is use a number of reference models used in clinical computing.

B.2 Clinical Computing Use

To Be Continued:

data types
class naming
domain archetype semantics versus LCD semantics of exchange models
mapping from C_DOMAIN_TYPE subtypes into various RMs

B.2.1 openEHR

B.2.2 CEN ENV13606

B.2.3 HL7 Clinical Document Architecture (CDA)

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References

Publications

1 Beale T. Archetypes: Constraint-based Domain Models for Future-proof Information Systems. OOPSLA 2002 workshop on behavioural semantics. Available at http://www.deepthought.com.au/it/archetypes.html.

2 Beale T. Archetypes: Constraint-based Domain Models for Future-proof Information Systems. 2000. Available at http://www.deepthought.com.au/it/archetypes.html .

3 Beale T, Heard S. The Archetype Definition Language (ADL). See http://www.openehr.org/re positories/spec-dev/latest/publishing/architecture/archetypes/lan guage/ADL/REV_HIST.html.

4 Heard S, Beale T. Archetype Definitions and Principles. See http://www.openehr.org/reposi tories/spec-dev/latest/publishing/architecture/archetypes/princi ples/REV_HIST.html.

5 Heard S, Beale T. The openEHR Archetype System. See http://www.openehr.org/reposito- ries/spec-dev/latest/publishing/architecture/archetypes/system/REV_HIST.ht ml .

6 Rector A L. Clinical Terminology: Why Is It So Hard? Yearbook of Medical Informatics 2001. 7 W3C. OWL - The Web Ontology Language. See http://www.w3.org/TR/2003/CR-owl-ref-20030818/ . 8 Horrocks et al. An OWL Abstract Syntax. See http://www.w3.org/xxxx/ .

Resources

9 openEHR. EHR Reference Model. See http://www.openehr.org/repositories/spec dev/latest/publishing/architecture/top.html. 10 OMG. The Object Constraint Language 2.0. Available at http://www.omg.org/cgi bin/doc?ptc/2003-10-14.

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