#34 Model RelationKind as its own type

[Martin]

Currently, the type of B.46 AbstractMetricDescriptor/Relation/@Kind is "restriction of xsd:string". Typically, we modelled such enumeration types as separate types, like for example B.441 MetricAvailability.

Formally, this makes no difference. However, it would harmonize our model and would create some more convenience in libraries being generated automatically from the schema.

[Stefan Schlichting]

Would need to be included in a revision of the schema. Hence, we leave the ticket open.

[David]

The reason this attribute appears as a restriction of string is because it is modeled as an inline data type. Pull this data type spec out of the attribute definition.