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Subject: Re: [wsbpel] Issue - 107 - Opacity and the meaning of nothingness inabstract processes

We need both, i.e. we should not enforce "consistent usage" of the implicit
or explicit mechanism.

(1) Sometimes you want to hide details of on internal process; even that
fact that "something happens" between two activities in the abstract
process.  Thus, we need implicit.

(2) The explicit is not only needed for "error detection" but also for
"templating" of process models.


Please respond to wsbpel@lists.oasis-open.org

To:    wsbpel@lists.oasis-open.org
Subject:    [wsbpel] Issue - 107 - Opacity and the meaning of nothingness
       in abstract processes

This issue has been added to the wsbpel issue list. The issues list is
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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

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

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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