README.OCL

-*- Text -*-
$Date: Sun, 18 Mar 2001 19:41:39 +0100 $
$ReleaseVersion: 2.3.1 $

This file documents issues related to the implementation of OCL in
USE.

* OCL semantics:

  - Note that some OCL operations are non-deterministic, e.g.,
    Set(T)->asSequence. The result of these operations are
    implementation dependent. The equation s1->asSequence =
    s1->asSequence will therefore be wrong in general.


* OCL extensions/variations:
  - Invariants can be marked as "existential", e. g.,
    context Person existential inv bossExists:
        self.isBoss = true
    When no instance of a person is created or no boss exists this 
    invariant will evaluate to false (instead of regular invariants,
    where the expression will evaluate to true, if no person is
    instantiated).

  - Invariants can have multiple variables, e. g.,
    context p1, p2:Person inv nameUnique:
        p1.name = p2.name implies p1 = p2
  
  - The undefined value (null) can be "upcasted" by specifying a type, e.g., 
    null(Integer). This is the shorthand notation for let i:Integer = null in i