Referencing in Asset Administration Shells

Overview

Two kinds of references are distinguished: references to external objects or entities (external reference) and references to model elements of the same or another Asset Administration Shell (model reference). Model references are also used for metamodel inherent relationships like submodels of an Asset Administration Shell (notation see Annex Concepts of the Administration Shell).

An external reference is a unique identifier. The identifier can be a concatenation of different identifiers, representing e.g. an IRDI-Path.

Note: references should not be mixed up with locators. Even URLs can be used as identifiers and do not necessarily describe a resource that can be accessed.

Reference Attributes

Metamodel of Reference
Figure 1. Metamodel of Reference

See Clause Matching Algorithm for References for reference matching.

Class:

Reference

Explanation:

Reference to either a model element of the same or another Asset Administration Shell or to an external entity

A model reference is an ordered list of keys, each key referencing an element. The complete list of keys may, for example, be concatenated to a path that gives unique access to an element.

An external reference is a reference to an external entity.

Inherits from:

 — 

ID:

https://admin-shell.io/aas/3/1/Reference

Attribute

ID

Explanation

Type

Card.

type

https://admin-shell.io/aas/3/1/Reference/type

Type of the reference

Denotes whether reference is an external reference or a model reference

ReferenceTypes

1

referredSemanticId

https://admin-shell.io/aas/3/1/Reference/referredSemanticId

Expected semantic ID of the referenced model element (Reference/type=ModelReference); there typically is no semantic ID for the referenced object of external references (Reference/type=ExternalReference).

Note 1: if Reference/referredSemanticId is defined, the semanticId of the model element referenced should have a matching semantic ID. If this is not the case, a validator should raise a warning.

Note 2: it is recommended to use an external reference for the semantic ID expected from the referenced model element.

Reference

0..1

key <<ordered>>

https://admin-shell.io/aas/3/1/Reference/keys

Unique reference in its name space

Key

1..*


Enumeration:

ReferenceTypes

Explanation:

Enumeration for denoting whether an element is an external or model reference

Set of:

 — 

ID:

https://admin-shell.io/aas/3/1/ReferenceTypes

Literal

ID

Explanation

ExternalReference

https://admin-shell.io/aas/3/1/ReferenceTypes/ExternalReference

External reference

ModelReference

https://admin-shell.io/aas/3/1/ReferenceTypes/ExternalReference/ExternalReference

Model reference

Key Attributes

Metamodel of Keys
Figure 2. Metamodel of Keys

Keys are used to define references (Reference).

Metamodel of KeyTypes Enumeration
Figure 3. Metamodel of KeyTypes Enumeration

Class:

Key

Explanation:

A key is a reference to an element by its ID

Inherits from:

 — 

ID:

https://admin-shell.io/aas/3/1/Key

Attribute

ID

Explanation

Type

Card.

type

https://admin-shell.io/aas/3/1/Key

Denotes which kind of entity is referenced

If Key/type = GlobalReference, the key represents a reference to a source that can be globally identified.

If Key/type = FragmentReference, the key represents a bookmark or a similar local identifier within its parent element as specified by the key that precedes this key.

In all other cases, the key references a model element of the same or another Asset Administration Shell. The name of the model element is explicitly listed.

KeyTypes

1

value

https://admin-shell.io/aas/3/1/Key

The key value, for example an IRDI or a URI or the idShort or any other fragment value

Identifier

1

An example for using a FragmentId as type of a key is a reference to an element within a file that is part of an Asset Administration Shell aasx package.

Metamodel of AasSubmodelElements Enumeration
Figure 4. Metamodel of AasSubmodelElements Enumeration

Enumeration:

KeyTypes

Explanation:

Enumeration of different key value types within a key

Set of:

FragmentKeys, AasReferables, GloballyIdentifiables

ID:

https://admin-shell.io/aas/3/1/KeyTypes

Literal

ID

Explanation

AnnotatedRelationshipElement

https://admin-shell.io/aas/3/1/KeyTypes/AnnotatedRelationshipElement

Annotated relationship element

AssetAdministrationShell

https://admin-shell.io/aas/3/1/KeyTypes/AssetAdministrationShell

Asset Administration Shell

BasicEventElement

https://admin-shell.io/aas/3/1/KeyTypes/BasicEventElement

Basic event element

Blob

https://admin-shell.io/aas/3/1/KeyTypes/Blob

Blob

Capability

https://admin-shell.io/aas/3/1/KeyTypes/Capability

Capability

ConceptDescription

https://admin-shell.io/aas/3/1/KeyTypes/ConceptDescription

Concept Description

DataElement

https://admin-shell.io/aas/3/1/KeyTypes/DataElement

Data Element

Note: data elements are abstract, i.e. if a key uses "DataElement", the reference may be a property, file, etc.

Entity

https://admin-shell.io/aas/3/1/KeyTypes/Entity

Entity

EventElement

https://admin-shell.io/aas/3/1/KeyTypes/EventElement

Event

Note: event element is abstract.

File

https://admin-shell.io/aas/3/1/KeyTypes/File

File

FragmentReference

https://admin-shell.io/aas/3/1/KeyTypes/FragmentReference

Bookmark or a similar local identifier of a subordinate part of a primary resource

GlobalReference

https://admin-shell.io/aas/3/1/KeyTypes/GlobalReference

Global reference

Identifiable

https://admin-shell.io/aas/3/1/KeyTypes/Identifiable

Identifiable

Note: identifiable is abstract, i.e. if a key uses "Identifiable" the reference may be an Asset Administration Shell, a submodel or a concept description.

MultiLanguageProperty

https://admin-shell.io/aas/3/1/KeyTypes/MultiLanguageProperty

Property with a value that can be provided in multiple languages

Operation

https://admin-shell.io/aas/3/1/KeyTypes/Operation

Operation

Property

https://admin-shell.io/aas/3/1/KeyTypes/Property

Property

Range

https://admin-shell.io/aas/3/1/KeyTypes/Range

Range with min and max

Referable

https://admin-shell.io/aas/3/1/KeyTypes/Referable

Note: referables are abstract, i.e. if a key uses "Referable", the reference may be an Asset Administration Shell, a property, etc.

ReferenceElement

https://admin-shell.io/aas/3/1/KeyTypes/ReferenceElement

Reference

RelationshipElement

https://admin-shell.io/aas/3/1/KeyTypes/RelationshipElement

Relationship

Submodel

https://admin-shell.io/aas/3/1/KeyTypes/Submodel

Submodel

SubmodelElement

https://admin-shell.io/aas/3/1/KeyTypes/SubmodelElement

Submodel element

Note: submodel elements are abstract, i.e. if a key uses "SubmodelElement", the reference may be a property, a submodel element list, an operation, etc.

SubmodelElementCollection

https://admin-shell.io/aas/3/1/KeyTypes/SubmodelElementCollection

Struct of submodel elements

SubmodelElementList

https://admin-shell.io/aas/3/1/KeyTypes/SubmodelElementList

List of submodel elements


Enumeration:

FragmentKeys

Explanation:

Enumeration of different fragment key value types within a key

Note: not used as type but in constraints.

Set of:

AASReferableNonIdentifiables, GenericFragmentKeys

ID:

https://admin-shell.io/aas/3/1/FragmentKeys

Literal

ID

Explanation

AnnotatedRelationshipElement

https://admin-shell.io/aas/3/1/FragmentKeys/AnnotatedRelationshipElement

Annotated relationship element

BasicEventElement

https://admin-shell.io/aas/3/1/FragmentKeys/BasicEventElement

Basic event element

Blob

https://admin-shell.io/aas/3/1/FragmentKeys/Blob

Blob

Capability

https://admin-shell.io/aas/3/1/FragmentKeys/Capability

Capability

DataElement

https://admin-shell.io/aas/3/1/FragmentKeys/DataElement

Data Element

Note: data elements are abstract, i.e. if a key uses "DataElement", the reference may be a property, file, etc.

Entity

https://admin-shell.io/aas/3/1/FragmentKeys/Entity

Entity

EventElement

https://admin-shell.io/aas/3/1/FragmentKeys/EventElement

Event

Note: event element is abstract.

File

https://admin-shell.io/aas/3/1/FragmentKeys/File

File

FragmentReference

https://admin-shell.io/aas/3/1/FragmentKeys/FragmentReference

Bookmark or a similar local identifier of a subordinate part of a primary resource

MultiLanguageProperty

https://admin-shell.io/aas/3/1/FragmentKeys/MultiLanguageProperty

Property with a value that can be provided in multiple languages

Operation

https://admin-shell.io/aas/3/1/FragmentKeys/Operation

Operation

Property

https://admin-shell.io/aas/3/1/FragmentKeys/Property

Property

Range

https://admin-shell.io/aas/3/1/FragmentKeys/Range

Range with min and max

ReferenceElement

https://admin-shell.io/aas/3/1/FragmentKeys/ReferenceElement

Reference

RelationshipElement

https://admin-shell.io/aas/3/1/FragmentKeys/RelationshipElement

Relationship

SubmodelElement

https://admin-shell.io/aas/3/1/FragmentKeys/SubmodelElement

Submodel element

Note: submodel elements are abstract, i.e. if a key uses "SubmodelElement", the reference may be a property, a submodel element list, an operation, etc.

SubmodelElementCollection

https://admin-shell.io/aas/3/1/FragmentKeys/SubmodelElementCollection

Struct of submodel elements

SubmodelElementList

https://admin-shell.io/aas/3/1/FragmentKeys/SubmodelElementList

List of submodel elements


Logical Enumerations

Figure 5 presents a logical model of key types. These logical enumerations may be used to formulate constraints.

Logical Model for Keys of References (non-normative)
Figure 5. Logical Model for Keys of References (non-normative)

Enumeration:

AasReferableNonIdentifiables

Explanation:

Enumeration of different fragment key value types within a key

Note: not used as type but in constraints.

Set of:

AasSubmodelElements

ID:

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables

Literal

ID

Explanation

AnnotatedRelationshipElement

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/AnnotatedRelationshipElement

Annotated relationship element

BasicEventElement

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/BasicEventElement

Basic event element

Blob

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/Blob

Blob

Capability

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/Capability

Capability

DataElement

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/DataElement

Data Element

Note: data elements are abstract, i.e. if a key uses "DataElement", the reference may be a property, file, etc.

Entity

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/Entity

Entity

EventElement

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/EventElement

Event

Note: event element is abstract.

File

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/File

File

MultiLanguageProperty

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/MultiLanguageProperty

Property with a value that can be provided in multiple languages

Operation

https://admin-shell.io/aas/3/1/AasSubmodelElements/Operation

Operation

Property

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/Property

Property

Range

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/Range

Range with min and max

ReferenceElement

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/ReferenceElement

Reference

RelationshipElement

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/RelationshipElement

Relationship

SubmodelElement

https://admin-shell.io/aas/3/1/AAasReferableNonIdentifiables/SubmodelElement

Submodel element

Note: submodel elements are abstract, i.e. if a key uses "SubmodelElement", the reference may be a property, a submodel element list, an operation, etc.

SubmodelElementCollection

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/SubmodelElementCollection

Struct of submodel elements

SubmodelElementList

https://admin-shell.io/aas/3/1/AasReferableNonIdentifiables/SubmodelElementList

List of submodel elements


Enumeration:

AasSubmodelElements

Explanation:

Enumeration of submodel element types including abstract submodel element types

Set of:

 — 

ID:

https://admin-shell.io/aas/3/1/AasSubmodelElements

Literal

ID

Explanation

AnnotatedRelationshipElement

https://admin-shell.io/aas/3/1/AasSubmodelElements/AnnotatedRelationshipElement

Annotated relationship element

BasicEventElement

https://admin-shell.io/aas/3/1/AasSubmodelElements/BasicEventElement

Basic event element

Blob

https://admin-shell.io/aas/3/1/AasSubmodelElements[/Blob

Blob

Capability

https://admin-shell.io/aas/3/1/AasSubmodelElements/Capability

Capability

DataElement

https://admin-shell.io/aas/3/1/AasSubmodelElements/DataElement

Data Element

Note: data elements are abstract, i.e. if a key uses "DataElement", the reference may be a property, file, etc.

Entity

https://admin-shell.io/aas/3/1/AasSubmodelElements/Entity

Entity

EventElement

https://admin-shell.io/aas/3/1/AasSubmodelElements/EventElement

Event

Note: event element is abstract.

File

https://admin-shell.io/aas/3/1/AasSubmodelElements/File

File

MultiLanguageProperty

https://admin-shell.io/aas/3/1/AasSubmodelElements/MultiLanguageProperty

Property with a value that can be provided in multiple languages

Operation

https://admin-shell.io/aas/3/1/AasSubmodelElements/Operation

Operation

Property

https://admin-shell.io/aas/3/1/AasSubmodelElements/Property

Property

Range

https://admin-shell.io/aas/3/1/AasSubmodelElements/Range

Range with min and max

ReferenceElement

https://admin-shell.io/aas/3/1/AasSubmodelElements/ReferenceElement

Reference

RelationshipElement

https://admin-shell.io/aas/3/1/AasSubmodelElements/RelationshipElement

Relationship

SubmodelElement

https://admin-shell.io/aas/3/1/AasSubmodelElements/SubmodelElement

Submodel element

Note: submodel elements are abstract, i.e. if a key uses "SubmodelElement", the reference may be a property, a submodel element list, an operation, etc.

SubmodelElementCollection

https://admin-shell.io/aas/3/1/AasSubmodelElements/SubmodelElementCollection

Struct of submodel elements

SubmodelElementList

https://admin-shell.io/aas/3/1/AasSubmodelElements/SubmodelElementList

List of submodel elements


Enumeration:

AasReferables

Explanation:

Enumeration of referables

Note: not used as type but in constraints.

Set of:

AASReferableNonIdentifiables, AasIdentifiables

ID:

https://admin-shell.io/aas/3/1/AasReferables

Literal

ID

Explanation

AnnotatedRelationshipElement

https://admin-shell.io/aas/3/1/AasReferables/AnnotatedRelationshipElement

Annotated relationship element

AssetAdministrationShell

https://admin-shell.io/aas/3/1/AasReferables/AssetAdministrationShell

Asset Administration Shell

BasicEventElement

https://admin-shell.io/aas/3/1/AasReferables/BasicEventElement

Basic event element

Blob

https://admin-shell.io/aas/3/1/AasReferables/Blob

Blob

Capability

https://admin-shell.io/aas/3/1/AasReferables/Capability

Capability

ConceptDescription

https://admin-shell.io/aas/3/1/AasReferables/ConceptDescription

Concept description

DataElement

https://admin-shell.io/aas/3/1/AasReferables/DataElement

Data element

Note: data elements are abstract, i.e. if a key uses "DataElement", the reference may be a property, file, etc.

Entity

https://admin-shell.io/aas/3/1/AasReferables/Entity

Entity

EventElement

https://admin-shell.io/aas/3/1/AasReferables/EventElement

Event

Note: event element is abstract.

File

https://admin-shell.io/aas/3/1/AasReferables/File

File

Identifiable

https://admin-shell.io/aas/3/1/AasReferables/Identifiable

Identifiable

Note: identifiables are abstract, i.e. if a key uses "Identifiable", the reference may be an Asset Administration Shell, a concept description, etc.

MultiLanguageProperty

https://admin-shell.io/aas/3/1/AasReferables/MultiLanguageProperty

Property with a value that can be provided in multiple languages

Operation

https://admin-shell.io/aas/3/1/AasReferables/Operation

Operation

Property

https://admin-shell.io/aas/3/1/AasReferables/Property

Property

Range

https://admin-shell.io/aas/3/1/AasReferables/Range

Range with min and max

Referable

https://admin-shell.io/aas/3/1/AasReferables/Referable

Note: referables are abstract, i.e. if a key uses "Referable", the reference may be an Asset Administration Shell, a property, etc.

ReferenceElement

https://admin-shell.io/aas/3/1/AasReferables/ReferenceElement

Reference

RelationshipElement

https://admin-shell.io/aas/3/1/AasReferables/RelationshipElement

Relationship

Submodel

https://admin-shell.io/aas/3/1/AasReferables/Submodel

Submodel

SubmodelElement

https://admin-shell.io/aas/3/1/AasReferables/SubmodelElement

Submodel element

Note: submodel elements are abstract, i.e. if a key uses "SubmodelElement", the reference may be a property, a submodel element list, an operation, etc.

SubmodelElementCollection

https://admin-shell.io/aas/3/1/AasReferables/SubmodelElementCollection

Struct of submodel elements

SubmodelElementList

https://admin-shell.io/aas/3/1/AasReferables/SubmodelElementList

List of submodel elements


Enumeration:

GenericFragmentKeys

Explanation:

Enumeration of generic fragment key value types within a key

Note: not used as type but in constraints.

Set of:

 — 

ID:

https://admin-shell.io/aas/3/1/GenericFragmentKeys

Literal

ID

Explanation

FragmentReference

https://admin-shell.io/aas/3/1/GenericFragmentKeys/FragmentReference

Bookmark or a similar local identifier of a subordinate part of a primary resource


Enumeration:

AasIdentifiables

Explanation:

Enumeration of all metamodel element types that represent identifiables

Note: not used as type but in constraints.

Set of:

 — 

ID:

https://admin-shell.io/aas/3/1/AasIdentifiables

Literal

ID

Explanation

AssetAdministrationShell

https://admin-shell.io/aas/3/1/AasIdentifiables/AssetAdministrationShell

Asset Administration Shell

ConceptDescription

https://admin-shell.io/aas/3/1/AasIdentifiables/ConceptDescription

Concept description

Identifiable

https://admin-shell.io/aas/3/1/AasIdentifiables/Identifiable

Identifiable

Note: Identifiables are abstract, i.e. if a key uses "Identifiable", the reference may be an Asset Administration Shell, a submodel, or a concept description.

Submodel

https://admin-shell.io/aas/3/1/AasIdentifiables/Submodel

Submodel


Enumeration:

GenericGloballyIdentifiables

Explanation:

Enumeration of different key value types within a key

Set of:

 — 

ID:

https://admin-shell.io/aas/3/1/GenericGloballyIdentifiables

Literal

ID

Explanation

GlobalReference

https://admin-shell.io/aas/3/1/GenericGloballyIdentifiables/GlobalReference

Global reference


Enumeration:

GloballyIdentifiables

Explanation:

Enumeration of globally identifiable elements

Set of:

https://admin-shell.io/aas/3/1/GenericGloballyIdentifiables, https://admin-shell.io/aas/3/1/AasIdentifiables

ID:

https://admin-shell.io/aas/3/1/GloballyIdentifiables

Literal

ID

Explanation

AssetAdministrationShell

https://admin-shell.io/aas/3/1/GloballyIdentifiables/AssetAdministrationShell

Asset Administration Shell

ConceptDescription

https://admin-shell.io/aas/3/1/GloballyIdentifiables/ConceptDescription

Concept description

GlobalReference

https://admin-shell.io/aas/3/1/GloballyIdentifiables/GlobalReference

Global reference

Identifiable

https://admin-shell.io/aas/3/1/GloballyIdentifiables/Identifiable

Identifiable

Note: Identifiables are abstract, i.e. if a key uses "Identifiable", the reference may be an Asset Administration Shell, a submodel, or a concept description.

Submodel

https://admin-shell.io/aas/3/1/GloballyIdentifiables/Submodel

Submodel


Constraints

Constraint AASd-121: For References, the value of Key/type of the first key of Reference/keys shall be one of GloballyIdentifiables.

Constraint AASd-122: For external references, i.e. References with Reference/type = ExternalReference, the value of Key/type of the first key of Reference/keys shall be one of GenericGloballyIdentifiables.

Constraint AASd-123: For model references, i.e. References with Reference/type = ModelReference, the value of Key/type of the first key of Reference/keys shall be one of AasIdentifiables.

Constraint AASd-124: For external references, i.e. References with Reference/type = ExternalReference, the last key of Reference/keys shall be either one of GenericGloballyIdentifiables or one of GenericFragmentKeys.

Constraint AASd-125: For model references, i.e. References with Reference/type = ModelReference with more than one key in Reference/keys, the value of Key/type of each of the keys following the first key of Reference/keys shall be one of FragmentKeys.

Note: constraint AASd-125 ensures that the shortest path is used.

Constraint AASd-126: For model references, i.e. References with Reference/type = ModelReference with more than one key in Reference/keys, the value of Key/type of the last Key in the reference key chain may be one of GenericFragmentKeys or no key at all shall have a value out of GenericFragmentKeys.

Constraint AASd-127: For model references, i.e. References with Reference/type = ModelReference with more than one key in Reference/keys, a key with Key/type FragmentReference shall be preceded by a key with Key/type _File or Blob. All other Asset Administration Shell fragments, i.e. Key/type values out of AasSubmodelElements , do not support fragments.

Note: which kind of fragments are supported depends on the content type and the specification of allowed fragment identifiers for the corresponding resource referenced.

Constraint AASd-128: For model references, i.e. References with Reference/type = ModelReference, the Key/value of a Key preceded by a Key with Key/type = SubmodelElementList is an integer number denoting the position in the array of the submodel element list.

In the following examples for valid und invalid model references and external references are given. The notation follows the grammar as defined in Clause Text Serialization of Values of Type "Reference".

Examples for valid references:

(Submodel)https://example.com/aas/1/1/1234859590

(GlobalReference)https://example.com/specification.html

Examples for valid external references:

(GlobalReference)https://example.com/ressource

(GlobalReference)0173-1#02-EXA123#001

(GlobalReference)https://example.com/specification.html (FragmentReference)Hints

Note:

(GlobalReference)https://example.com/specification.html (FragmentReference)Hints

represents the path with fragment identifier

https://example.com/specification.html#Hints

Examples for valid model references:

(AssetAdministrationShell)https://example.com/aas/1/0/12348

(Submodel)https://example.com/aas/1/1/1234859590

(Submodel)https://example.com/aas/1/1/1234859590, (File)Specification

(ConceptDescription)0173-1#02-BAA120#008

(Submodel)https://example.com/aas/1/1/1234859590, (SubmodelElementList)Documents, (SubmodelElementCollection)0, (MultiLanguageProperty)Title

(Submodel)https://example.com/aas/1/1/1234859590, (SubmodelElementCollection)Manual, (MultiLanguageProperty)Title

Note:

(SubmodelElementCollection)0, (MultiLanguageProperty)Title

may be identical to

(SubmodelElementCollection)Manual, (MultiLanguageProperty)Title

semantically and content-wise. The difference is that more than one document is allowed in the first submodel and thus a submodel element list is defined: elements in a list are numbered. However, it is also possible to define a display name in this case. The display name of the SubmodelElementCollection should be the same in both bases, e.g. "Users Manual".

(Submodel)https://example.com/aas/1/1/1234859590, (File)Specification, (FragmentReference)Hints

Note: assuming the file has the value using the absolute path

https://example.com/specification.html

(and not a relative path), the first reference points to the same information as the global reference

(GlobalReference)https://example.com/specification.html, (FragmentReference)Hints
(Submodel)https://example.com/aas/1/1/1234859590, (Blob)Specification, (FragmentReference)Hints

Examples for invalid model references:

(GlobalReference)https://example.com/aas/1/1/1234859590

This is an external reference but no model reference.

(Property)0173-1#02-BAA120#008

This reference does not start with the ID of an Identifiable. Additionally, the value is not valid idShort for a Property submodel element.

(Submodel)https://example.com/aas/1/1/1234859590, (EventElement)Event, (FragmentReference)Comment

This model reference is invalid because fragment references so far are only defined for File and Blob submodel elements (see Constraint AASd-127).

(AssetAdministrationShell)https://example.com/aas/1/0/12348, (Submodel)https://example.com/aas/1/1/1234859590, (Property)Temperature

This is not a valid model reference because AssetAdministrationShell and Submodel are both global identifiables.