wiki:Support Information Model 4 Identification Package

Identification Package

4.1 Overview

The package describes a model of references and identifiers for information entities and is illustrated in FIGURE 5 .


FIGURE 5 Package

4.1.1 Requirements

Identification of entities both in the real world and in information systems is a non-trivial problem. The needs for identification across systems in a health information environment include the following:

  • real world identifiers such as social security numbers, veterans affairs ids etc can be recorded as required by health care facilities, enterprise policies, or legislation;
  • identifiers for informational entities which represent real world entities or processes should be unique;
  • it should be possible to determine if two identifiers refer to information entities that represent the same real world entity, even if instances of the information entities are maintained in different systems;
  • versions or changes to real-world entity-linked informational entities (which may create new information instances) should be accounted for in two ways:

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  • it should be possible to tell if two identifiers refer to distinct versions of the same

informational entity in the same version tree;

  • it should not be possible to confuse same-named versions of informational entities

maintained in multiple systems which purport to represent the same real world

entity. E.g. there is no guarantee that two systems’ “latest” version of the Person

“Dr Jones” is the same.

Medico-legal use of information relies on previous states of information being

distinguishable from other previous states and the current state.

  • It should be possible for an entity in one system or service (such as the EHR) to refer to an entity in another system or service in such a way that: -the target of the reference is easily finable within the shared environment, and
  • the reference does is valid regardless of the physical architecture of servers and applications.

The following subsections describe some of the features and challenges of identification.

Identification of Real World Entities (RWEs)

Real world entities such as people, car engines, invoices, and appointments can all be assigned identifiers. Although many of these are designed to be unique within a jurisdiction, they are often not, due to data entry errors, bad design (ids that are too small or incorporate some non-unique characteristic of the identified entities), bad process (e.g. non-synchronised id issuing points); identity theft (e.g. via theft of documents of proof or hacking). In general, while some real world identifiers (RWIs) are “nearly unique”, none can be guaranteed so. It should also be the case that if two RWE identifiers are equal, they refer to the same RWE, but this is often not the case. For practical purposes, RWIs cannot be regarded as computationally safe for making the inferences described here.

Identification of Informational Entities (IEs)

As soon as information systems are used to record facts about RWEs, the situation becomes more complex because of the intangible nature of information. In particular:

  • the same RWE can be represented simultaneously on more than one system (‘spatial multiplicity’);
  • the same RWE may be represented by more than one “version” of the same IE in a system (‘temporal multiplicity’).

At first sight, it appears that there can also be purely informational entities, i.e. IEs which do not refer to any RWE, such as books, online-only documents and software. However, as soon as one considers an example it becomes clear that there is always a notional ‘definitive’ or ‘authoritative’ (i.e. trusted) version of every such entity. These entities can better be understood as ‘virtual RWEs’. Thus it can still be said that multiple IEs may refer to any given RWE.

The underlying reason for the multiplicity of IEs is that ‘reality’ - time and space - in computer systems is not continuous but discrete, and each ‘entity’ is in fact just a snapshot of certain attribute values of a RWE, at a point in time, in a particular system. If identifiers are assigned to IEs without regard to versions or duplicates, then no assertion can be made about the identified RWE when two IE ids are compared.

Identification of Versions

The notion of ‘versioning’ applies only to informational entities, i.e. distinct instances of content each representing a snapshot of some logical entity. Where such instances are stored and managed in versioned containers within a versioning system of some kind, explicit identification of the versions is

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required. The requirements are discussed in detail in the Common IM, change_control package. They can be summarised as follows:

  • it must be possible to distinguish two versions of the same logical entity, i.e. know from the identifier if they are the same or different versions of the same thing;
  • it must be possible to distinguish two versions of the same logical entity created in two distinct systems;
  • it must be possible to tell the relationship between the items in a versioned lineage, from the version identifiers.

Referencing of Informational Entities

Within a distributed information environment, there is a need for entities not connected by direct references in the same memory space to be able to refer to each other. There are two competing requirements:

  • that the separation of objects in a distributed computing environment not compromise the semantics of the model;
  • that different types of information can be managed relatively independently; for example EHR and demographic information can be managed by different groups in an organisation or community, each with at least some freedom to change implementation and model details.

4.2 Design

This package models only informational identifiers, i.e. transparent identifiers understood by openEHR or related computational systems. Real World Entity Identifiers such as driver’s license numbers are modelled using the data type DV_IDENTIFIER. This is not to imply that such identifiers are any less systematic or well-managed than the system identifiers defined here, only that from the point of view of openEHR, they have the same status as other informational attributes such as name, address etc of a Person.

A key design decision has been to choose a string representation for all identifiers, with subparts being made available by appropriate functions which perform simple parsing on the string. This ensures that the data representation of identifiers (e.g. in XML) is as small as possible, while not losing object-oriented typing.

4.2.1 Primitive Identifiers

Three kinds of types are defined in this package. The abstract UIDtype and its subtypes correspond to permanent, computationally reliable, primitive identifiers. Such identifiers are regarded as ‘primitive’ because they are treated as having no further internal structure, in the sense that part of such an identifier is not in general meaningful. The three subtypes UUID, ISO_OID and INTERNET_ID all have these properties, and are commonly accepted ways of uniquely identifying entities in computer systems. In openEHR (and generally in health informatics) they are usually used as parts of other identifiers.

A consequence of the string representation approach used in these classes is that to set an attribute of type UID from a string value, as would be done when reading from a database, deserialising from XML or another text form, a piece of code that inspects the string structure has to be used in order to decide which of the subtypes of UID it is. This is a safe thing to do, since all three subtypes have mutually exclusive string patterns, and can easily be distinguished.

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4.2.2 Composite Identifiers

The OBJECT_ID type and its hierarchy of subtypes correspond to composite identifier types whose structure and semantics are defined by openEHR (rather than external organisations), and are the main means of identifying information items in an openEHR system. The abstract type UID_BASED_IDand its two subtypes HIER_OBJECT_IDand OBJECT_VERSION_IDprovide respectively, UID-based identifiers for non-versioned and versioned items. The design of the latter subtype is explained in the openEHR Common IM, change_control package.

The other subtypes, ARCHETYPE_ID and TERMINOLOGY_ID define different kinds of identifier, the former being a multi-axial identifier for archetypes, and the latter being a globally unique single string identifier for terminologies. The ARCHETYPE_ID class explicitly includes archetype version as part of the identifier, while terminology identifier values are assumed to include this, either as part of the name (e.g. as is done in the US National Library of Medicine UMLS identifiers - see ), or according to the syntax defined in section 4.3.12 below.

Identifying Versions

The OBJECT_VERSION_ID defines the semantics of the scheme used in openEHR for identifying versions, and uses a three-part identifier, consisting of:

  • object_id: the identifier of the version container, in the form of an UID;
  • version_tree_id: the location in the version tree, as a 1- or 3-part numeric identifier, where the latter variant expresses branching; this is modelled using the VERSION_TREE_ID type;
  • creating_system_id: the identifier of the system in which this version was created, or type UID.

Under this scheme, multiple versions in the same container all have the same value for object_id, while their location in the version tree is given by the combination of the version tree identifier and the identifier of the creating system.

The requirements on the third part of the identifier are that it be unique per system, and that it be easy to obtain or generate. It is also helpful if it is a meaningful identifier. The two most practical candidates appear to be GUIDs (which are not meaningful, but are easy to generate) and reverse internet domain identifiers, as recommended in [3] (these are easy to determine if the system has an internet address, and are meaningful and directly processible, however unconnected systems pose a problem). ISO Oids might also be used. All of these identifier types are accommodated via the use of UID.

A full explanation of the version identification scheme and its capabilities is given in the change_control section of the Common IM.

4.2.3 References

All OBJECT_IDs are used as identifier attributes within the thing they identify, in the same way as a database primary key. To refer to an identified object from another object, an instance of the class OBJECT_REF should generally be used, in the same way as a database foreign key. The class OBJECT_REF is provided as a means of distributed referencing, and includes the object namespace (typically !1:1 with some service, such as “terminology”) and type. The general principle of object references is to be able to refer to an object available in a particular namespace or service. Usually they are used to refer to objects in other services, such as a demographic entity from within an EHR, but they may be used to refer to local objects as well. The type may be the concrete type of the referred-to object (e.g. “GP”) or any proper ancestor (e.g. “PARTY”).

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4.3 Class Descriptions

4.3.1 UID Class

CLASSUID (abstract)
PurposeAbstract parent of classes representing unique identifiers which identify information entities in a durable way. UIDs only ever identify one IE in time or space and are never re-used.
HL7The HL7v3 UID Data type.
value: StringThe value of the id.
InvariantValue_exists: value /= Void and then not value.empty

4.3.2 ISO_OID Class

PurposeModel of ISO’s Object Identifier (oid) as defined by the standard ISO/IEC 8824 . Oids are formed from integers separated by dots. Each non-leaf node in an Oid starting from the left corresponds to an assigning authority, and identifies that authority’s namespace, inside which the remaining part of the identifier is locally unique.
HL7The HL7v3 OID Data type.

4.3.3 UUID Class

PurposeModel of the DCE Universal Unique Identifier or UUID which takes the form of hexadecimal integers separated by hyphens, following the pattern 8-4-4-4-12 as defined by the Open Group, CDE 1.1 Remote Procedure Call specification, Appendix A. Also known as a GUID.
HL7The HL7v3 UUID Data type.

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4.3.4 INTERNET_ID Class

PurposeModel[[BR]of a reverse internet domain, as used to uniquely identify an internet
domain. In the form of a dot-separated string in the reverse order of a
domain name, specified by IETF RFC 1034 (]
Invariant Syntax

According to IETF RFC1034, the syntax of a domain name follows the BNF grammar:

domain: subdomain | ‘ ’ subdomain: label | subdomain ‘.’ label label: letter [ [ ldh-str ] let-dig ] ldh-str: let-dig-hyp | let-dig-hyp ldh-str let-dig-hyp: let-dig | ‘-’ let-dig: letter | digit

letter: any one of the 52 alphabetic characters A through Z in upper case and a through z in lower case

digit: any one of the ten digits 0 through 9

It can also be expressed using the regular expression:


4.3.5 OBJECT_ID Class

PurposeAncestor class of identifiers of informational objects. Ids may be completely meaningless, in which case their only job is to refer to something, or may carry some information to do with the identified object.
UseObject ids are used inside an object to identify that object. To identify another object in another service, use an OBJECT_REF, or else use a UID for local objects identified by UID. If none of the subtypes is suitable, direct instances of this class may be used.

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value: StringThe value of the id in the form defined below.
InvariantValue_exists: value /= Void and then not value.empty

4.3.6 UID_BASED_ID Class

PurposeAbstract model of UID-based identifiers consisting of a root part and an optional extension; lexical form: root ‘::’ extension
1..1root: UIDThe identifier of the conceptual namespace in which the object exists, within the identification scheme. Returns the part to the left of the first ‘::’ separator, if any, or else the whole string.
1..1extension: StringOptional local identifier of the object within the context of the root identifier. Returns the part to the right of the first ‘::’ separator if any, or else any empty String.
has_extension: BooleanTrue if extension /= Void
InvariantRoot_valid: root /= Void Extension_validity: extension /= Void Has_extension_validity: extension.is_empty xor has_extension Identifier Syntax

The syntax of the value attribute by default follows the following production rules (EBNF):

value: root [ ‘::’ extension ] root: uid -- see UID above extension: string

4.3.7 HIER_OBJECT_ID Class

Concrete type corresponding to hierarchical identifiers of the form defined by UID_BASED_ID.

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HL7The HL7v3 II Data type.


PurposeGlobally unique identifier for one version of a versioned object; lexical form: object_id ‘::’ creating_system_id ‘::’ version_tree_id
1..1object_id: UIDUnique identifier for logical object of which this identifier identifies one version; normally the object_id will be the unique identifier of the version container containing the version referred to by this OBJECT_VERSION_ID instance.
1..1version_tree_id: VERSION_TREE_IDTree identifier of this version with respect to other versions in the same version tree, as either 1 or 3 part dot-separated numbers, e.g. “1”, “2.1.4”.
1..1creating_system_id: UIDIdentifier of the system that created the Version corresponding to this Object version id.
is_branch: BooleanTrue if this version identifier represents a branch.
InvariantsObject_valid: object_id /= Void Version_tree_id_valid: version_tree_id /= Void creating_system_id_valid: creating_system_id /= Void Identifier Syntax

The string form of an OBJECT_VERSION_ID stored in its value attribute consists of three segments separated by double colons (“::”), i.e. (EBNF):

value: object_id ‘::’ creating_system_id ‘::’ version_tree_id object_id: uid -- see UID below creating_system_id:

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An example is as follows:



PurposeVersion tree identifier for one version. Lexical form: trunk_version [ ‘.’ branch_number ‘.’ branch_version ]
1..1value: StringString form of this identifier.
1..1trunk_version: StringTrunk version number; numbering starts at 1.
0..1branch_number: StringNumber of branch from the trunk point; numbering starts at 1.
0..1branch_version: StringVersion of the branch; numbering starts at 1.
1..1is_branch: BooleanTrue if this version identifier represents a branch, i.e. has branch_number and branch_version parts.
1..1is_first: BooleanTrue if this version identifier corresponds to the first version, i.e. trunk_version = “1”
InvariantsValue_valid: value /= Void and then not value.is_empty Trunk_version_valid: trunk_version /= Void and then trunk_version.is_integer and then trunk_version.as_integer >= 1 Branch_number_valid: branch_number /= Void implies branch_number.is_integer and then branch_number.as_integer >= 1 Branch_version_valid: branch_version /= Void implies branch_version.is_integer and then branch_version.as_integer >= 1 Branch_validity: (branch_number = Void and branch_version = Void ) xor (branch_number /= Void and branch_version /= Void ) Is_branch_validity: is_branch xor branch_number = Void Is_first_validity: not is_first xor trunk_version.is_equal(“1”) Syntax

The format of the value attribute is (EBNF):

value: trunk_version [ ‘.’ branch_number ‘.’ branch_version ] trunk_version: { digit }+ branch_number: { digit }+ branch_version: { digit }+

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4.3.10 ARCHETYPE_ID Class

PurposeIdentifier for archetypes. Lexical form: rm_originator ‘-’ rm_name ‘-’ rm_entity ‘.’ concept_name { ‘-’ specialisation }* ‘.v’ number
1..1qualified_rm_entity: StringGlobally qualified reference model entity, e.g. “openehr-composition-OBSERVATION”.
1..1domain_concept: StringName of the concept represented by this archetype, including specialisation, e.g. “biochemistry_result-cholesterol”.
1..1rm_originator: StringOrganisation originating the reference model on which this archetype is based, e.g. “openehr”, “cen”, “hl7”.
1..1rm_name: StringName of the reference model, e.g. “rim”, “ehr_rm”, “en13606”.
1..1rm_entity: StringName of the ontological level within the reference model to which this archetype is targeted, e.g. for openEHR, “folder”, “composition”, “section”, “entry”.
1..1specialisation: StringName of specialisation of concept, if this archetype is a specialisation of another archetype, e.g. “cholesterol”.
1..1version_id: StringVersion of this archetype.
InvariantQualified_rm_entity_valid: qualified_rm_entity /= Void and then not qualified_rm_entity.is_empty Domain_concept_valid: domain_concept /= Void and then not domain_concept.is_empty Rm_originator_valid: rm_originator /= Void and then not rm_originator.is_empty Rm_name_valid: rm_name /= Void and then not rm_name.is_empty Rm_entity_valid: rm_entity /= Void and then not rm_entity.is_empty Specialisation_valid: specialisation /= Void implies not specialisation.is_empty Version_id_valid: version_id /= Void and then not version_id.is_empty

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Support Information Model Identification Package Rev 1.6.0 Archetype ID Syntax

Archetype identifiers are “multi-axial”, meaning that each identifier instance denotes a single archetype within a multi-dimensional space. In this case, the space is essentially a versioned 3-dimensional space, with the dimensions being:

  • reference model entity, i.e. target of archetype
  • domain concept
  • version

As with any multi-axial identifier, the underlying principle of an archetype id is that all parts of the id must be able to be considered immutable. This means that no variable characteristic of an archetype

(e.g. accrediting authority, which might change due to later accreditation by another authority, or may be multiple) can be included in its identifier. The syntax of an ARCHETYPE_ID is as follows (EBNF):

archetype_id: qualified_rm_entity ‘.’ domain_concept ‘.’ version_id

qualified_rm_entity: rm_originator ‘-’ rm_name ‘-’ rm_entity rm_originator: V_NAME rm_name: V_NAME rm_entity: V_NAME

domain_concept: concept_name { ‘-’ specialisation }* concept_name: V_NAME specialisation: V_NAME

version_id: ‘v’ V_NUMBER

NUMBER: [0-9]* NAME: [a-z][a-z0-9()/%$#&]*

The field meanings are as follows:

rm_originator: id of organisation originating the reference model on which this archetype is based;

rm_name: id of the reference model on which the archetype is based;

rm_entity: ontological level in the reference model;

domain_concept: the domain concept name, including any specialisations;

version_id: numeric version identifier;

Examples of archetype identifiers include:

  • openehr-composition-SECTION.physical_examination.v2 • openehr-composition-SECTION.physical_examination-prenatal.v1
  • hl7-rim-act.progress_note.v1 • openehr-composition-OBSERVATION.progress_note-naturopathy.v2

Archetypes can also be identified by other means, such as ISO oids.

4.3.11 TEMPLATE_ID Class

Identifier for templates. Lexical form to be determined.

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PurposeIdentifier for terminologies such accessed via a terminology query service. In this class, the value attribute identifies the Terminology in the terminology service, e.g. “SNOMED-CT”. A terminology is assumed to be in a particular language, which must be explicitly specified. The value if the id attribute is the precise terminology id identifier, including actual release (i.e. actual “version”), local modifications etc; e.g. “ICPC2”. Lexical form: name [ ‘(’ version ‘)’ ]
1..1name: StringReturn the terminology id (which includes the “version” in some cases). Distinct names correspond to distinct (i.e. non-compatible) terminologies. Thus the names “ICD10AM” and “ICD10” refer to distinct terminologies.
1..1version_id: StringVersion of this terminology, if versioning supported, else the empty string.
InvariantsName_valid: name /= Void and then not name.is_empty Version_id_valid: version_id /= Void Identifier Syntax

The syntax of the value attribute is as follows:

name [ ‘(’ version ‘)’ ]

Examples of terminology identifiers include:

  • “snomed-ct”
  • “ICD9(1999)”

Versions should only be needed for those terminologies which break the rule that the thing being identified with a code loses or changes its meaning over versions of the terminology. This should not be the case for well known modern terminologies and ontologies, particularly those designed since the publication of Cimino’s ‘desiderata’ [1] of which the principle of “concept permanance” is appli-

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cable here - “A concept's meaning cannot change and it cannot be deleted from the vocabulary”. However, there maybe older terminologies, or specialised terminologies which may not have obeyed these rules, but which are still used; version ids should always be used for these.

4.3.13 GENERIC_ID Class

PurposeGeneric identifier type for identifiers whose format is othterwise unknown to openEHR. Includes an attribute for naming the identification scheme (which may well be local).
1..1scheme: StringName of the scheme to which this identifier conforms. Ideally this name will be recognisable globally but realistically it may be a local ad hoc scheme whose name is not controlled or standardised in any way.
InvariantsScheme_valid: scheme /= Void and then not scheme.is_empty

4.3.14 OBJECT_REF Class

PurposeClass describing a reference to another object, which may exist locally or be maintained outside the current namespace, e.g. in another service. Services are usually external, e.g. available in a LAN (including on the same host) or the internet via Corba, SOAP, or some other distributed protocol. However, in small systems they may be part of the same executable as the data containing the Id.
1..1id: OBJECT_ID Globally unique id of an object, regardless of where it is stored.
1..1namespace: StringNamespace to which this identifier belongs in the local system context (and possibly in any other openEHR compliant environment) e.g. “terminology”, “demographic”. These names are not yet standardised. Legal values for the namespace are “local” | “unknown” | “[a-zAZ][a-zA-Z0-9_-:/&+?]*”

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1..1type: StringName of the class (concrete or abstract) of object to which this identifier type refers, e.g. “PARTY”, “PERSON”, “GUIDELINE” etc. These class names are from the relevant reference model. The type name “ANY” can be used to indicate that any type is accepted (e.g. if the type is unknown).
InvariantId_exists: id /= Void Namespace_exists: namespace /= Void and then not namespace.is_empty Type_exists: type /= Void and then not type.is_empty


PurposeReference to access group in an access control service.
InvariantType_validity: type.is_equal(“ACCESS_GROUP”)

4.3.16 PARTY_REF Class

PurposeIdentifier for parties in a demographic or identity service. There are typically a number of subtypes of the PARTY class, including PERSON, ORGANISATION, etc. Abstract supertypes are allowed if the referenced object is of a type not known by the current implementation of this class (in other words, if the demographic model is changed by the addition of a new PARTY or ACTOR subtypes, valid PARTY_REFs can still be constructed to them).
FunctionsSignature Meaning Type_validity: type.is_equal(“PERSON”) or type.is_equal(“ORGANISATION”) or type.is_equal(“GROUP”) or type.is_equal(“AGENT”)or type.is_equal(“ROLE”) or type.is_equal(“PARTY”) or type.is_equal(“ACTOR”)

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4.3.17 LOCATABLE_REF Class

PurposeReference to a LOCATABLE instance inside the top-level content structure inside a VERSION<T>; the path attribute is applied to the object that points to.
1..1 (redefined)id: OBJECT_VERSION_IDThe identifier of the Version.
0..1path: StringThe path to an instance in question, as an absolute path with respect to the object found at An empty path means that the object referred to by id being specified.
1..1as_uri: StringA URI form of the reference, created by concatenating the following: “ehr://” + id.value + “/” + path
InvariantPath_valid: path /= Void implies not path.is_empty

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