Service Template versioning. More specifically, model instance versioning (versus the entities being represented by the model). This kind of versioning treats a Service Template as a single unit (or entity instance) for which we may want to attach a version attribute. The version attribute would imply nothing more than some chronologic ordering in some version domain. Note that it possible to version at a finer granularity such as the Node/Relationship Templates or even versioning sub groups of these as a version set (I am not implying we should do this). The key idea is that we are implying that version n+1 was created based on a copy of version n and we assume this is important information to use to discriminate lineage and compatibility, i.e. that a user or software component may want to select by version.