Handling of Identifiers

The VEC and its XML Schema offer different concepts for the identification of model elements addressing certain requirements and those shall be used accordingly.

Identification-Properties (VEC Model)

Many types defined in the VEC model have an “Identification” property (e.g. the OccurrenceOrUsage). This is meant to be a semantic identifier of the object represented by the VEC element. The following rules apply to those identifiers:

1. The expectations defined in the documentation of the VEC model of the corresponding attribute shall be ensured.
2. The identifications shall be unique for a certain element type, at least within its context element. In other words, the VEC model and its representation as XML Schema is a hierarchical data model. That means, that an identification shall be at least unique within its direct parent element (e.g. the identification of a HousingComponent shall be unique within its EEComponentSpecification.
3. Two elements of different types can have the same Identification. However, this is only recommended, when the two VEC elements represent the same domain entity from different points of view, otherwise this shall be avoided as far as possible.
4. In general, it is recommended to keep the Identifications stable over the time. This means, that if an object is exported multiple times the Identification of it should be the same. However, this is not possible in all cases, for all processes and all tools. Therefore, a process and / or tool creating VEC files should describe for all elements, under which conditions Identifications are stable or new ones are created.

AliasIdentification-Properties (VEC Model)

Certain elements have the capability to define AliasIdentifications in addition to their unique identifications. AliasIdentifications are scoped identifiers of the object. The scope can be a system, a company or or process. One use case of this kind of ids is the creation of traceability links between different sources of information. Examples for usages of the AliasIdentifications are:

• The identifier of a connector in the electrological process (with geometric variants)
• The identifier of a node or segment in a MCAD tool
• An assigned UUID of an element.

id-Attributes (XML Representation)

All xs:complexType define an id-Attribute with the type xs:ID. These are technical ids that are necessary for the referencing mechanism of the VEC within a single XML file. The semantics, constraints and requirements are defined by the XML Standard and XML Schema itself. These ids do not have any significance outside a VEC file. See the Section id-Attibutes.

immutable-global-id-Attributes (XML Repesentation)

See the Section immutable-global-id-Attributes.

IRIs (RDF Representation)

In RDF all objects (named resources in RDF) require a global unique identifiers which is an IRI. This is mandatory for resource to be “referencable”. The maturity of the IRI generation strategy decides quality & stability of links within RDF graphs. There it should be thoroughly thought through when representing VEC data in RDF. The RDF IRI is very similiar to the immutable-global-id feature in VEC XML representations. When mapping VEC data from XML to RDF and back, it should be possible to use immutable-global-id (when defined), as RDF IRI and vice versa.

However, RDF IRIs are a standard concept defined in RDF, whereas the immutable-global-id are a specific feature of the VEC XML representation.