The reader who is familiar with database transaction might find this term misleading. Classical ``ACID'' database transactions have four properties:
  • Atomicity: a transaction must be accomplished as a whole or not at all.
  • Consistency: the result of a transaction must be predictable and reproductable.
  • Isolation: no transaction must interfere with any other concurrently executing transaction.
  • Durability: the result of changes operated by a transaction must be permanent.
The semantics of EPOS transactions does not enforce these properties as they are at all. The fact that EPOS users deal with database stored data justifies the use of the term, but the different natures of the two kind of transactions should be kept in mind troughout the reading of the thesis.

This term, even though commonly used within the Object-Orientation community, is not part of the EPOS terminology and, therefore, is used here only for sake of clarity. The EPOS counterparts of the term are, obviously, type and meta-type

This sintax has not been implemented yet. The real SPELL consists of Prolog predicates, for the time being

Passani Luca
Mon Feb 20 21:59:27 MET 1995