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Paper Details

%T Algebras of Actions in Concurrent Processes
%A Mark Burgin, Marc L. Smith
%E Alistair A. McEwan, Steve Schneider, Wilson Ifill, Peter H. Welch
%B Communicating Process Architectures 2007
%X We introduce a high\-level metamodel, EAP
   (event\-action\-process), for reasoning about concurrent
   processes. EAP shares with CSP notions of observable events
   and processes, but as its name suggests, EAP is also
   concerned with actions. Actions represent an intermediate
   level of event composition that provide the basis for a
   hierarchical structure that builds up from individual,
   observable events, to processes that may themselves be
   units of composition. EAP&\[sh]8217;s
   composition hierarchy corresponds to the reality that
   intermediate units of composition exist, and that these
   intermediate units don&\[sh]8217;t always fall neatly
   within process boundaries. One prominent example of an
   intermediate unit of composition, or action, is threads.
   Threads of execution are capable of crossing process
   boundaries, and one popular programming paradigm,
   object\-oriented programming, encourages this approach to
   concurrent program design. While we may advocate for
   more disciplined, process\-oriented design, the demand for
   better models for reasoning about threads remains. On a
   more theoretical level, traces of a computation are also
   actions. Traces are event structures, composed by the CSP
   observer, according to a set of rules for recording the
   history of a computation. In one of the
   author&\[sh]8217;s model for viewcentric reasoning
   (VCR), the CSP observer is permitted to record
   simultaneous events without interleaving; and in previous
   joint work by the authors, the extended VCR (EVCR) model
   permits the CSP observer to record events with duration,
   so that events may overlap entirely, partially, or not at
   all. Sequential composition may be viewed as a special case
   of parallel composition&\[sh]8212;one of many forms
   of composition we wish to be better able to reason
   about. Since such diverse types of composition exist, at
   the event, action, and process levels; and because such
   problematic actions as threads exist in real systems,
   we must find more appropriate models to reason about such
   systems. To this end, we are developing algebras at
   different levels of compositionality to address these
   goals. In particular, we are interested in a corresponding
   hierarchy of algebras, at the event, action, and process
   levels. The present focus of our efforts is at the action
   level, since these are the least well understood. This talk
   presents fundamental notions of actions and examples
   of actions in the context of real systems. A diversity of
   possible compositions at the action level will be revealed
   and discussed, as well as our progress on the
   action algebra itself.

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