Issue - 107 - Opacity and the meaning of nothingness in abstract processes

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Issue - 107 - Opacity and the meaning of nothingness in abstract processes
Status: open

Area: Abstract processes

Date added: 18 Mar 2004

Submitter: Yaron Y. Goland

Date submitted: 18 March 2004

Description: The design of abstract processes requires the ability to omit 
information that is not relevant to the abstract process's design. There 
are two general strategies for omitting information - implicit and explicit.

An example of implicitly hiding data is the way that abstract processes 
deal with some of the variables on message operations. If one doesn't 
want to specify where a message is recorded on a receive then one may 
simply leave off the variable attribute.

An example of explicitly hiding data would be introducing something like 
an <opaque> activity. For example, imagine that one is defining an 
abstract process and the start activities of the abstract process are to 
be omitted since they are not relevant to the functionality the abstract 
process is describing. In that case one could start a process with an 
<opaque> activity. By putting in <opaque> one is explicitly 
communicating to the reader of the abstract process 'There is something 
here but its definition is not relevant to the goal of the abstract 
process.'

The advantage of explicit versus implicit hiding is in error detection.

In an implicit system where one simply leaves off variables or omits 
activities there is no way to tell the difference between an error, e.g. 
the person intended to include the variable or activity but forget and 
true omission. This is a well known problem with treating the absence of 
information as information.

In an explicit system where one would have <opaque> activities and 
special reserved bpel:opaque place holders for attributes there is no 
possibility for confusion. If an opaque value is specified then one has 
an unambiguous declaration from the designer of the abstract process as 
to their intention.

The issue before the group is - should we consistently use an implicit 
or explicit omission mechanism for specifying when information has been 
intentionally omitted in an abstract process?

Changes: 18 Mar 2004 - new issue

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