[wsia][wsrp-interfaces] Uniqueness of handles

[Rich Thompson <richt2@us.ibm.com>]

Carsten raised a question that was included in the v0.22 draft spec as a
comment on page 13, line 30. I would break this into 2 questions:

1) Uniqueness: Will we REQUIRE that all handles at a particular scope (eg.
consumerHandles) be unique?
  Advantages:
    - Deterministic behaviour when releasing the handle. If 2 handles could
have the same value, which is being released?
    - Deterministic behaviour when generating content. If 2 entity handles
may the same value, which is to be used?
 Disadvantages:
    - Restricts means by which the Producer may generate the handle. In
particular, this could not be just a serialization of some portion of the
state the handle refers to.


2) Invariance: Will we REQUIRE that all handles are invariant once created?
Namely, do we forbid the modify operation from touching the handle?
 Advantages:
    - Much simpler processing for the Consumer. If the handle could be
modified, all the places it is referenced (pages, databases, ...) would
have to be located and updated.
    - If the handle can change AND it is currently in use by an End-User,
does a call with the old one fail?
 Disadvantages:
    - Restricts means by which the Producer may generate the handle. In
particular, this could not be just a serialization of some portion of the
state the handle refers to.


I'm sure I've missed some advantages/disadvantages, but I would prefer both
uniqueness and invariance.