The original mechanism for loading mappings from a context was done while we were developing SubjectSession and is woefully inflexible and out of date.

To replace it, the new instance management in ThingSession is required since there are networks of mappings all over the place and resolving them is now simple.

Rather than passing in a context, making a subject session then making triples by hand, new helper things are made to encapsulate the vocabulary and a thing session is passed around.