111 research outputs found
Revisiting sequential composition in process calculi
International audienceThe article reviews the various ways sequential composition is defined in traditional process calculi, and shows that such definitions are not optimal, thus limiting the dissemination of concurrency theory ideas among computer scientists. An alternative approach is proposed, based on a symmetric binary operator and write-many variables. This approach, which generalizes traditional process calculi, has been used to define the new LNT language implemented in the CADP toolbox. Feedback gained from university lectures and real-life case studies shows a high acceptance by computer-science students and industry engineers
State-of-the-art on evolution and reactivity
This report starts by, in Chapter 1, outlining aspects of querying and updating resources on
the Web and on the Semantic Web, including the development of query and update languages
to be carried out within the Rewerse project.
From this outline, it becomes clear that several existing research areas and topics are of
interest for this work in Rewerse. In the remainder of this report we further present state of
the art surveys in a selection of such areas and topics. More precisely: in Chapter 2 we give
an overview of logics for reasoning about state change and updates; Chapter 3 is devoted to briefly describing existing update languages for the Web, and also for updating logic programs;
in Chapter 4 event-condition-action rules, both in the context of active database systems and
in the context of semistructured data, are surveyed; in Chapter 5 we give an overview of some relevant rule-based agents frameworks
Proposition Algebra with Projective Limits
Sequential propositional logic deviates from ordinary propositional logic by
taking into account that during the sequential evaluation of a propositional
statement,atomic propositions may yield different Boolean values at repeated
occurrences. We introduce `free valuations' to capture this dynamics of a
propositional statement's environment. The resulting logic is phrased as an
equationally specified algebra rather than in the form of proof rules, and is
named `proposition algebra'. It is strictly more general than Boolean algebra
to the extent that the classical connectives fail to be expressively complete
in the sequential case. The four axioms for free valuation congruence are then
combined with other axioms in order define a few more valuation congruences
that gradually identify more propositional statements, up to static valuation
congruence (which is the setting of conventional propositional logic).
Proposition algebra is developed in a fashion similar to the process algebra
ACP and the program algebra PGA, via an algebraic specification which has a
meaningful initial algebra for which a range of coarser congruences are
considered important as well. In addition infinite objects (that is
propositional statements, processes and programs respectively) are dealt with
by means of an inverse limit construction which allows the transfer of
knowledge concerning finite objects to facts about infinite ones while reducing
all facts about infinite objects to an infinity of facts about finite ones in
return.Comment: 43 pages, 3 table
Extending and Relating Semantic Models of Compensating CSP
Business transactions involve multiple partners coordinating and interacting with each other. These transactions have hierarchies of activities which need to be orchestrated. Usual database approaches (e.g.,checkpoint, rollback) are not applicable to handle faults in a long running transaction due to interaction with multiple partners. The compensation mechanism handles faults that can arise in a long running transaction. Based on the framework of Hoare's CSP process algebra, Butler et al introduced Compensating CSP (cCSP), a language to model long-running transactions. The language introduces a method to declare a transaction as a process and it has constructs for orchestration of compensation. Butler et al also defines a trace semantics for cCSP. In this thesis, the semantic models of compensating CSP are extended by defining an operational semantics, describing how the state of a program changes during its execution. The semantics is encoded into Prolog to animate the specification. The semantic models are further extended to define the synchronisation of processes. The notion of partial behaviour is defined to model the behaviour of deadlock that arises during process synchronisation. A correspondence relationship is then defined between the semantic models and proved by using structural induction. Proving the correspondence means that any of the presentation can be accepted as a primary definition of the meaning of the language and each definition can be used correctly at different times, and for different purposes. The semantic models and their relationships are mechanised by using the theorem prover PVS. The semantic models are embedded in PVS by using Shallow embedding. The relationships between semantic models are proved by mutual structural induction. The mechanisation overcomes the problems in hand proofs and improves the scalability of the approach
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