Evolution of Object Behavior Using Context Relations

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Evolution of Object BehaviorUsing Context
Relations

• Linda M. Seiter, Member, IEEE Computer Society,
  Jens Palsberg,
• and Karl J. Lieberherr, Member, IEEE
• IEEE TRANSACTIONS ON SOFTWARE ENGINEERING,
• VOL. 24, NO. 1, JANUARY 1998
• 2002/7/24
• Presented by Kim, Cheol-ho

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Contents

• Introduction
• Internal Contexts Dynamic Object Behavior
• Call Contexts Dynamic Collaborative Behavior
• Related Work
• Application of the Context Relation
• Conclusion

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Introduction(1/2)
1) explicit delegation along aggregation
relations 2) creation of auxiliary structures
and hierarchies 3) violation of class
encapsulation.

• Design Pattern
• design reuse
• identify variant aspects of system and propose a
  way of applying them in programs
• To support dynamic behavior
• class-based approach
• prototype-based approach

1) inability to ensure type safety 2) inability
to override existing behavior in a controlled
manner 3) negative performance impact
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Introduction(2/2)

• Context Relation
• support behavioral evolution while maintaining
  the safety and performance benefits available
  with strongly typed, class-based languages
• to include context relation, extend UML at design
  level and Java at language level
• demonstrate how the context relation can be used
  to easily model and program numerous design
  patterns

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Internal Contexts Dynamic Object Behavior(1/4)

• structural and behavioral patterns that benefit
  from the context relation can be categorized
• based on altering a single object,
• based on altering a class (affecting all
  instances)
• To safely achieve dynamic behavior at both the
  object and class level, object oriented languages
  must support
• instance-stored versus class-stored specification
• dynamic specification
• dynamic update

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Internal Contexts Dynamic Object Behavior(2/4)

• Instance-Stored Specification
• Dynamic Specification

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Internal Contexts Dynamic Object Behavior(3/4)

• Dynamic Update
• Type Checking Class Update Specifications
• dynamic method implementation should be executed
  on the receiver object as well as the context
  object
• implicit self reference (this pointer in Java)
  refers to the receiver object
• a new keyword context to refer to the implicit
  context object

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Internal Contexts Dynamic Object Behavior(4/4)

• Java Syntax
• Proposed java syntax
• Example class definitions

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Call Contexts Dynamic Collaborative
Behavior(1/4)

• how to alter the behavior of a group of
  collaborating objects
• attaching a context to a method invocation
• implicitly alter all class instances encountered
  during the call

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Call Contexts Dynamic Collaborative
Behavior(2/4)

• Visitor Pattern

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Call Contexts Dynamic Collaborative
Behavior(3/4)

• Visitor Pattern Using Context Relations

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Call Contexts Dynamic Collaborative
Behavior(4/4)

• Visitor Comparison

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Related Work(1/2)

• Evolving Object Interfaces and Behavior
• Perspectives, Views, contexts, mode
• Evolving Collaborative Behavior
• Frameworks, Clusters, Mechanisms, Contracts,
  Propagation patterns, Subjects
• Java/C Approach
• Separating an interface from an implementation
• Dynamic binding

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Related Work(2/2)

• CLOS Approach
• multidispatch mechanisms
• Reflection
• use a metaobject protocol to implement the
  context relation
• Rather than extend the syntax of a language, a
  metaobject protocol could be used to alter the
  semantics of dynamic binding

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Application of the Context Relation

• A special case of the context relation has been
  implemented in Demeter/Java
• Demeter/Java visitor implementation has been used
  successfully in a commercial project at GTE
  Laboratories
• traversal/visitor style used in Demeter/Java has
  been used successfully in a commercial C
  project at Hewlett-Packard
• Other features which have not been implemented in
  Demeter/Java
• dynamic class extension

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Conclusion

• To model and implement the evolution of behavior,
  this paper propose the context relation as an
  extension to the existing object-oriented model
• Context relation is meaningful
• at design, implementation levels and software
  testing
• dynamic boundary
• the base class along with its contexts
  representing the dynamic class definition