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Subject: 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 posted as a Technical Committee document to the OASIS WSBPEL TC pages on a regular basis. The current edition, as a TC document, is the most recent document with the title in the "Issues" folder of the WSBPEL TC document list - the next posting will include this issue. The list editor's working copy, which will normally include an issue when it is announced, is available at this constant URL.

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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