p-Method: A Model-Driven Formal Method for Architecture-Centric Software Engineering

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p-Method A Model-Driven Formal Method for
Architecture-Centric Software Engineering

• By Flavio Oquendo
• Presented by Sajith Wickramaratne

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p-Method

• This article presents the p-Method, a formal
  method that has been designed in the ArchWare
  European Project to address model-driven
  development of safe software systems.
• It is a well-defined theoretical method relying
  on formal foundations.
• It supports formal model-driven development of
  software systems having highly dynamic
  architectures.
• Its formal language for architecture is based on
• Architecture description p-calculus.
• Architecture analysis µ-calculus.
• Architecture transformation and refinement
  Rewriting logic.

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p-Method vs. Other formal methods

• Formal methods such as B, FOCUS, VDM, and Z, aim
  to provide full support for formal development of
  software systems.
• However, these methods do not provide any
  architectural support.
• p-Method has been built from scratch to formally
  support architecture-centric component-based
  model-driven development.

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Completeness and Correctness of Software Systems

• Support the formal specification of software
  systems whose architecture can change (at
  run-time).
• Support automated analysis functional as well as
  non-functional properties.
• Support their transformations and application
  synthesis, by stepwise refinement from abstract
  to concrete specifications and full code
  generation.
• Support compliance with respect to application
  requirements (if requirements change, enable the
  software system to safely progress with new
  requirements).

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p-Method

• Why Formal?
• Improves documentation and understanding of
  specifications.
• Enables rigorous analysis of the system
  properties.
• Improves rigour and quality of the whole
  development process.
• Provides a firm foundation during the evolution
  process.

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p-Method

• Why Architecture-Centric?
• A key aspect of the design of any software system
  is its architecture.
• Fundamental organization of the system embodied
  in its components, their relationships to each
  other, and to the environment, and the principles
  guiding its design and evolution.
• Provides the conceptual abstraction for modeling
  complex software systems during development and
  then during deployment and evolution
• Why Model-Driven Engineering?
• Models are used to understand specific system
  aspects.
• Predicts system qualities.
• Reasons about impact of changes.
• Indicates major system features to stakeholders.

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Approach of the p-Method

• The novelty of the p-Method lies in its holistic
  view of formal software development.
• It involves
• how the software is to function in terms of
  expected behaviours.
• what is its structure in terms of components
  and their connectors.
• which qualities are to be guaranteed.
• Furthermore, an appropriate refinement process
  (describing how to build the software).

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Architecture-centric formal development
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Architecture-centric formal development

• Define style activities
• Principal actors are the style architects.
• Represent the top level inception of a family of
  software architectures.
• What types of architectural elements.
• How elements can be combined.
• Which constraints apply, and which processes can
  be applied to architecture elements and whole
  architecture descriptions.
• Describe architecture activities
• Principal actors are the application
  architects.
• Use the domain specific styles defined by the
  style architect to describe a specific software
  architecture.
• An architecture description, in terms of a model.
• Can represent a system at various levels of
  abstractions.
• Refine architecture activities
• Principal actors are the application engineers.
• Support transformations from abstract to more
  concrete architecture descriptions.
• Derive concrete models by applying correctness
  preserving transformations.

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Model transformations with p-ARL
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Formal Languages

• p-ADL an architecture description language based
  on the higher-order typed p-calculus.
• p-AAL an architecture analysis language based on
  the µ-calculus.
• p-ARL an architecture refinement language based
  on the rewriting logic.

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The triad of formal languages
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The Architecture Description Language p-ADL

• Architecture Description Language encompasses
  two aspects expression and verification of
  architectural styles.
• General principles guided the design of p-ADL
• Formality p-ADL (formal language) provides a
  formal system, at the mathematical sense, for
  describing dynamic software architectures.
• Run-time viewpoint p-ADL focuses on the formal
  description of software architectures from the
  run-time viewpoint structure, behavior, and how
  these may evolve over time.
• Executability p-ADL(executable language) is a
  virtual machine that runs specifications of
  software architectures.
• User-friendliness p-ADL supports different
  concrete syntaxes textual and graphical
  notations (including UML-based) .

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p-ADL

• Design principles
• The principle of correspondence.
• The principle of abstraction.
• The principle of data type completeness.
• Civil rights in the language
• The right to be declared.
• The right to be assigned.
• The right to have equality defined over them.
• The right to persist.

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The Architecture Analysis Language p-AAL

• Architecture Analysis Language focuses two
  aspects
• Architectural styles (style architects)
• Software Architectures (application architects).
• Properties of styles and architectures.
• structural (e.g. cardinality of architectural
  elements, interconnection topology)
• behavioral (e.g. safety, liveness, and fairness
  defined on actions of the system).
• The p-AAL is a formal property expression
  language designed to support automated
  verification.
• Can mechanically check whether an architecture
  described in p-ADL satisfies property expressed
  in p-AAL.

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The Architecture Refinement Language p-ARL

• The concrete architecture Vertical and
  Horizontal transformations.
• Horizontal refinement is obtained from
  transforming an architecture by partition.
• Vertical refinement is obtained from transforming
  steps to add more details to abstract models
  until the concrete architectural model is
  described.
• The p-Method (ARL) supports both horizontal and
  vertical refinements.
• p- ARLs four forms of refinement from an
  external or internal point of view
• behavior refinement
• port refinement
• structure refinement
• data refinement

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Application domains of the p-Method

• The p-Method (p-ADL, p-AAL, and p-ARL) have been
  applied in the following application domains
• software systems targeting J2EE platforms.
• enterprise application integration systems.
• grid computing systems.
• human-computer interfaces for monitoring
  systems.
• mobile agent systems.
• sensor-actuator networks.
• service-oriented architectures.
• ambient intelligence.

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Related Work for p-Method

• Architecture Description (ADLs)
• ACME, AESOP,AML,ARMANI,CHAM-ADL,
  DARWIN,META-H,PADL,RAPIDE,SADL, sp-SPACE,
  UNICON-2,andWRIGHT/Dynamic-WRIGHT.
• Architecture Analysis (AALs)
• PDL, LOTOS, CADP and CCS.
• Architecture Transformation and
  Refinement(ARLs)
• FOCUS,RAPIDE, SADL, B and Z.

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Future Work in p-Method

• p-Modeller a tool to support visual description
  of software architectures in p-ADL
• p-Animator a tool to support graphical animation
  of software architectures described in p-ADL.
• p-Analyser a tool to support verification of
  structural and behavioural properties specified
  in p-AAL against software architectures described
  in p-ADL.
• p-Refiner a tool to support refinements of
  software architectures described in p-ADL.
• p-Synthesiser a tool to support code generation
  from concrete architecture descriptions in p-ADL.
  
• p-ADL Compiler and Virtual Machine.
• p-TraceChecker.

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Conclusion

• p-Method recognizes architecture-centric
  model-driven approaches, supported by adequate,
  compositional, formal languages and tools.
• It involves p-ADL, p-AAL, and p-ARL to support
  architectural description, analysis, refinement,
  and code generation.
• p-Method cost-effectively develops and evolves
  software systems while guaranteeing their
  completeness and correctness.