Synchronization strategies for global computing models

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Synchronization strategiesfor global computing
models
Ivan Lanese Computer Science Department University
of Bologna
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Roadmap

• Application field global computing
• The main tool graphs and SHR
• Some contributions
• Parametric synchronization
• Compositionality properties
• Relations with Fusion Calculus
• And after?

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What is global computing?

• Essentially networks deployed on huge areas
• Global computing systems quite common nowadays
• Internet, wireless communication networks,

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Challenges of global computing systems

• Distribution, mobility, heterogeneity, openness,
  reconfigurability, non-functional requirements
• Traditional formal methods are not enough
• Strong emphasis on coordination among subsystems
• Mobility must be modeled explicitly
• Need for compositionality and high abstraction

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Synchronized Hyperedge Replacement

• We want to model systems as graphs
• Components are edges
• Links are common nodes
• Behaviour specified by transitions
• Derived from the behaviour (productions) of
  single components
• Keep into account synchronization and
  communication/mobility

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Hyperedge Replacement Systems

• A production describes how the hyperedge L is
  rewritten into the graph R

L
R
H
3
3
4
4
2
2
1
1
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Hyperedge Replacement Systems

• A production describes how the hyperedge L is
  transformed into the graph R

Many concurrent rewritings are allowed
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Synchronizing productions

• Synchronization productions execute actions on
  nodes. Actions on the same node should be
  compatible
• Two existing synchronization models Milner
  (message passing) and Hoare (agreement)

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Milner SHR

• Milner synchronization pair of edges can
  synchronize by performing complementary actions

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SHR with mobility
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Example
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Algebraic presentation of SHR

• Helps the development of the theory
• Proofs by induction
• Graphs represented as terms in an algebra
• Edges are basic constants
• Operators for composing them
• Transitions described by a labelled transition
  system
• Inference rules to derive transitions from
  productions

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Parametric synchronization

• The expressive powers of Hoare and Milner
  synchronizations are not comparable
• Can specify different classes of reconfigurations
• Is it possible to find some more general
  framework?
• Winskel proposed synchronization algebras to
  describe general synchronizations
• Not suitable for synchronizations with mobility
• We generalize them to SAMs (Synchronization
  Algebras with Mobility)

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Synchronization Algebras with Mobility
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Synchronization Algebras with Mobility

• SAs specify composition of actions
• (a,a,t) a synchronizes with a producing t
• SAMs also provide
• Mapping from parameters of synchronizing actions
  to parameters of the result
• Fusions among parameters
• Some more technical stuff

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Milner SAM on 2 actions

• in, out, t, e
• (in, out, t)
• (a, e, a)

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Parametric SHR

• The SAM is a parameter of the model
• Different models obtained via instantiation
• Allows to recover Hoare and Milner SHR
• and to easily define new models
• Properties can be proved for any SAM or for a
  class of SAMs
• Many SAMs can be used in the same model
• Useful to model heterogeneous systems

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Compositionality for parametric SHR

• Bisimulation allows to observe interactions of a
  system with the environment
• Can be defined in a standard way for SHR
• Bisimulation is a congruence for SHR with most
  SAMs
• Behaviour of a system can be inferred from the
  behaviour of its components

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Fusion Calculus

• Calculi for mobility allow to model concurrent
  and mobile systems
• p-calculus is the most used
• Fusion Calculus generalizes and simplifies it
• More symmetric
• Shared-state update

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Milner SHR vs Fusion Calculus

• Apparently very different models
• Some important similarities
• Synchronization in Milner style
• Mobility using fusions
• Faithful mapping of Fusion into Milner SHR
• SHR is more general
• Graphical presentation
• Multiple synchronizations
• Concurrent semantics

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Fusion Calculus vs Milner SHR

• Fusion Milner SHR
• Processes Graphs
• Sequential processes Hyperedges
• Names Nodes
• Comm. primitives Productions
• Transitions Interleaving tr.

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Example
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Exploitation of the mapping

• The results obtained for SHR can be applied to
  Fusion Calculus
• PRISMA Calculus Fusion SAMs
• The semantics of Fusion induced by the mapping is
  compositional
• The result does not hold for the standard
  semantics
• The trick is concurrency

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Future work

• Some applications to p-calculus
• Analysis of the concurrent semantics of
  p-calculus
• Application of SAMs to p-calculus
• From global computing to service oriented
  computing
• In service oriented computing services are
  discovered, invoked and composed
• Which are the correct primitives to model them?
• Which are the interesting properties and
  equivalences?

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End of talk

• Thanks

• Questions?