SCE — Category class - various

Section 8.2.3 first para,
TYPO: "A Category, which have user-defined semantics" have -> has

Figure 12 caption
TYPO: ".. a Groups referencing Categories ..."

General comment: Categories, as described and illustrated in the examples seems like a terminological device, very similar to vocabularies. If vocabularies were not flat, i.e. items could relate to other items via the IS-A (subsumption) relation, then the effect of Categories could be achieved just by allowing SCEElements to have SemanticReferences as their categories / classifiers. Any vocabulary that is extensible, e.g. RelationshipKind is in reality likely to be extended with both new top-level terms and specialised forms of some of the existing terms.

John Butler (09-04-2022): Good point. Could just use SemanticReference as the type of the property “category” on SCEElement and then it could be as rich as one would want.

Property RelationshipDirection:
ERROR: the backward and none enumeration literals have the same definition.

Fix typos related to Category

Fix typos as identified in the issue.