OCL25 — Clarify LocalSnapshot / History

Fig 10.2 presents some classes that to the best of my knowledge have never been used in an OCL implementation. The LocalSnapshot is a possible way of reconciling the need for two distinct system states when evaluating @pre or oclIsNew. It is however perhaps no more than some draft thoughts. Some much more promising work has evolved as 'Filmstrip's in conjunction with the USE tool. A Filmstrip supports OCL expressions that apply across time.

The LocalSnapshot and associated support are absolutely not a normative part of an OCL implementation.