Hydra (A General Framework for Formalizing UML with Formal Languages for Embedded Systems*)

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Hydra(A General Framework for Formalizing UML
with Formal Languages for Embedded Systems)

• from the Ph.D. thesis of
• William E. McUmber
• Software Engineering and Network Systems Lab
• Michigan State University

This work has been supported in part by National
Science Foundation grants (CCR-9901017,
CCR-9633391, CCR-9407318), a DARPA grant, and
Eaton Corporation.
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Hydra Tool Overview

• Hydra parses a textual representation of an
  integrated collection of Unified Modeling
  Language (UML) graphical diagrams that represent
  a model of the system.
• Hydras textual input format, Hydra Intermediate
  Language (HIL), allows Hydra to remain
  independent from optional graphical front ends.
• It then generates appropriate formal
  specifications in the desired target
  specification language. Formal languages
  supported include VHDL and Promela, the input
  language for Bell Labs model checker SPIN.

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Theoretical Basis for Hydra

• Underlying the Hydra tool is a general framework
  for formalizing UML diagrams with formal
  languages.
• This framework defines a homomorphic mapping
  between a unified metamodel for UML class and
  state diagrams and a metamodel for the target
  formal language.
• A metamodel is a class diagram that describes the
  constructs of a modeling language and the
  relationships between the constructs.
• Homomorphisms preserve structure, so the mapping
  rules are complete.

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Unified UML Metamodel
Model
Class
Relationships
Behavior
State Vertex
Instance Variables
Aggregation
Generalization
Transition
Association
Rest of dynamic model
Class diagram related
State diagram related
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Homomorphic Mapping
Formal language metamodel
UML metamodel
Homomorphism
Constrains Diagrams
Constrains Rules
Constrains Model
Formal specification of system
UML diagrams
Mapping Rules
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Semantics

• UML does not attach formal semantics to diagrams.
  
• Without a fixed semantics, it is not possible to
  apply rigorous automated analysis such as
  simulation or model checking to UML diagrams.
• The Hydra framework attaches a specific semantics
  to the UML diagrams from a range of possible
  semantics, thus enabling the derivation of formal
  language specifications and the application of
  automated analysis techniques.

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Unified Modeling Language

• UML is a collection of graphical object-oriented
  modeling notations for visually depicting various
  aspects of a software system. Hydra integrates
  two
• Class Diagrams depict system structure classes
  (boxes) and relationships between them (adorned
  lines).
• State Diagrams depict object behavior events on
  transitions (directed arcs) can cause a change of
  state (rounded rectangles).

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Class and State Diagrams
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Architecture of Hydra
HIL1
Spec
Parser
Target language specific class library
1 Hydra Intermediate Language Hydra can
automatically generate formal specifications for
a number of target languages, including VHDL and
Promela. The class library used would be
appropriate for the target language.
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Using Hydra
Analysis results
UML
HIL
Spec
Optional graphical editor
Analysis tool
Hydra
Hydra can automatically generate formal
specifications for a number of target languages,
including VHDL and Promela. The analysis tool
used would be appropriate for the target
language.
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Simulation and Model Checking

• Simulation of a collection of UML diagrams via
  its formal specification enables the developer to
  validate behavioral requirements and to debug the
  system design. It is a useful technique,
  especially early in the diagram construction
  process. However, simulation is not exhaustive.
• Model checking is, in general, an exhaustive
  technique that covers the entire state space of
  possible executions of the system. Using SPIN,
  for example, this technique can find deadlocks
  and unreachable states, test system invariants
  against the model, and verify temporal claims.

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Applications and Future Work

• Hydra has been used to model a furnace controller
  in both VHDL and Promela, and a Smart Cruise
  Control system in Promela.
• Current investigations include creating a
  metamodel and mapping rules for SMV, the input
  language for Clarkes Symbolic Model Verifier
  (another model checking tool).
• A complementary system, MINERVA, is currently
  under development both as a graphical front-end
  to the Hydra tool and as a visualization
  environment for analysis results.