Intentional Constraint Automata

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Context

• REO a channel-based coordination model for
  component composition. MSCS, 14(3)329366, 2004
• Language was introduced in 2001
• Farhad Arbab and Jan J.M.M. Rutten. A coinductive
  calculus of component connectors. In Recent
  Trends in Algebraic Development Techniques 16th
  International Workshop, volume 2755 of LNCS,
  pages 3455. Springer-Verlag GmbH, November 2003.
• Farhad Arbab, Christel Baier, Jan Rutten, and
  Marjan Sirjani. Modelling component connectors in
  REO by Constraint Automata. In Proceedings of
  FOCLASA 2003, a satellite event of CONCUR 2003,
  volume 97 of ENTCS, pages 2546. Elsevier
  Science, July 2004
• Dave Clarke, David Costa, Farhad Arbab. Connector
  Colouring I Synchronization and Context
  Dependency. To appear in proceedings of FOCLASA
  2005, a satellite event of CONCUR 2005, San
  Francisco, California, Aug. 2005.

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Plan

• REO (fastest introduction ever)
• Connectors
• Example
• Constraint Automata
• Definition
• Features
• Example
• Problem
• Intensional Constraint Automata
• Definition
• Example
• Envisaged results

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REO

• Exogenous Coordination Language
• For software component composition
• Channel based (open set and user defined)
• Allows to define circuit-like component connectors

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REO component connectors

• Connector act as glue code
• Connect
• Coordinate
• Coordinate through the interplay of
• Data-flow1
• Synchronisation and Mutual exclusion1
• Context Dependency2
• 1 correctly modelled in Constraint Automata
• 2 not properly handled by Constraint Automata

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Connector example

• Exclusive Router

C1
C2
C3
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Components/Connectors Interaction

• Components interact with a connector performing
• I/O-operation requests on the connectors ports.
• Depending on the specification and actual
  configuration of the connector an I/O-operation
  request can be accepted and the I/O operation
  succeed (observable)
• wait until either the connector evolves to a
  configuration in which this waiting operation can
  succeed or
• time-out. (not covered)

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Constraint Automata (CA)
Data Constraint grammar, A 2 Names, d 2 Data
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CA Features

• CA framework
• Provides a compositional semantics for REO
  circuits.
• Defining operators that mimic REOs operations
  for join and hiding.
• Can be used as a semantic model to describe the
  TDS-language induced by Reo connector networks.
• Provides various notions of equivalence, forming
  a foundation for algorithms and tools for
  verification and derivation of properties of REO
  connectors.

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Example and Problem

• LossySync channel modelled using CA.
• Two alternative transitions are possible
• Either I/O operations on ports A and B
  simultaneously succeed and data is transferred.
• or only the I/O operation on port A succeeds and
  data is lost.
• Undesirably this automaton not accurately models
  the LossySync behaviour

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Intensional semantics

• Computational Comonads and Intensional Semantics.
  Stephen Brookes and Shai Geva, 1991.
• Introduces a general category-theoretic framework
  that allows to establish sensible relationships
  between the extensional and intensional semantics
  of a particular language.

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Intensional Constraint Automata (IntCA)

• In IntCA a state represents a configuration of
  the connector and contains the information about
  ports with pending I/O-operations. A state of the
  form qP is a configuration q where ports Ap 2 P
  have pending I/O-operations.
• A transition is a possible one-step behaviour
  where the meaning of
• is that in configuration qP1 the ports
  
• have the possibility to perform their I/O
  operations, if they meet the guard g, and that
  lead to configuration pP2, where the ports Ap 2
  P2 have I/O pending operations.

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Modelling the LossySync

• CA accepted dataflow
• IntCA enforced order of requests, the enforced
  protocol by the comunication by the connector

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Envisaged Results

• Conjecture
• We can still use a automata model to model REO
  connectors when in the presence of context
  dependent behaviour. We need a finer automata
  model (less abstract)
• What is the Intensional TDS language induced by
  Reo connectors?
• Is it possible to extract the Extensional
  language from the Intensional one?
• Whether exists a natural way of relating all
  intensional constraint automata with the same
  extensional part.
• Perhaps an equivalence relation on intensional
  constraint automata