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Subject: Issue 107 - further clarification/details/more spec-y
Expanding on Peter's existing 107 proposal (details, syntax, examples), assuming concepts in 82 (base+profiles) : ---------------------------------------------------------------- 15.1 Language extensions for Abstract Processes The language extensions consist of opaque 'placeholders'. Note that "opaque" is not a new semantically meaningful construct but a syntactic device for indicating incompleteness. As such, "opaque" entities have no semantics of their own. There are three kinds of opaque placeholders: expressions, activities, and attributes. A usage profile may decrease the allowed level of opacity at its discretion, but may not increase it above what is allowed by the "common base". -Under the 'common base' section --------------------------------- Three types of opaque tokens are allowed in abstract processes: activities, expressions, and attributes. The functions of these opaque placeholders are described below, with examples: Part A - Opaque activities: An opaque activity explicitly hides a concrete BPEL activity whose behavior is not relevant to the recipient/user of the abstract process. An opaque activity is a BPEL activity and therefore has the same standard elements and attributes that all BPEL activities have (see spec section 11.1 and 11.2). It has the following form: <opaque standard-attributes> standard-elements </opaque> One examples of using opaque activities includes creating process templates (marking the points of normative extension in a process). Another is when creating an abstract process from a known executable process and wanting to hide an activity that is a join point for several links. If that activity, on the other hand, had just been an unlinked activity in a 'sequence' it could have just been omitted from the resulting abstract process. At first glance, it seems that this could instead be done using "empty". The difference is that "empty" explicitly says "nothing happens here," whereas "opaque" is really saying "something happens here, but it's hidden on purpose". A.1 Level of opacity allowed in the base: Opaque activities are allowed. PART B - Opaque expressions: Opaque BPEL expressions shall be allowed exclusively for the use of abstract processes. An opaque expression explicitly hides a concrete BPEL expression. An example usage of an opaque expression is that of copying a hidden value into a known variable. Opaque assignment can be used to express non-determinism: the obvious case being a process that needs to show a decision point with alternative outcomes without specifying how the decision is reached. In this case the expressions that constrain each branch may need to be left unspecified, but it may also be convenient to make a specific value or quantity such as a price threshold unspecified, so that explicitly specified conditions relative to the threshold become non-deterministic as a result of the threshold value being unknown. All expressions in BPEL, and their corresponding opaque representations are listed below: 1-Boolean valued expressions: -Transition Condition: <transitionCondition expressionLanguage="anyURI"? opaque="yes"/> -Join Condition: <joinCondition expressionLanguage="anyURI"? opaque="yes"/> -While Condition: <condition expressionLanguage="anyURI"? opaque="yes"/> -Switch Case Condition: <case> <condition expressionLanguage="anyURI"? opaque="yes"/> activity </case> 2- Deadline valued expressions: -Until element of onAlarm and wait: <until expressionLanguage="anyURI"? opaque="yes"/> -Opaque assignment (<from opaque="yes">) is used for capturing variable creation/modification in a yet-to-be-concretized mechanism/fashion. 3- Duration valued expressions: -For element of onAlarm and wait: <for expressionLanguage="anyURI"? opaque="yes"/> -repeatEvery element of onAlarm: <repeatEvery expressionLanguage="anyURI"? opaque="yes"/> 4- General Expressions: -Expressions in 'from-spec' in an assign activity: <from><expression expressionLanguage="anyURI"? opaque="yes"/> *Special case for generic opaque assignment: <from opaque="yes"> is allowed, and represents hiding any of the forms of the 'from-spec'. See section 9.3. B.1 Level of opacity in the common base: All BPEL expressions are allowed to be opaque. The generic form of opaque assignment is also allowed. PART C - Opaque attributes: An opaque attributes hide the value of a concrete BPEL attribute. For example, an opaque variable attribute in a receive activity hides where the data is stored once the corresponding message is received. The reserved value "##BPELopaque" shall be made available for use as the value of any BPEL attributes in a BPEL abstract process that accept a QNAME or NCNAME. The reserved value's semantics are that it is a place holder for some other QNAME/NCNAME. C.1: The level of opacity in the common base: All BPEL attributes are allowed to be opaque in the common base. --------- Rania's note on spec editing : if 82 passes, then A.1, B.1, and C.1 could go in the bullets of the common base where it says that it depends on 107.