Traversing the Design Gap with Patterns

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Traversing the Design Gapwith Patterns

• Mark Verhappen,
• Jeroen Voeten,
• Piet van der Putten

June 17, 2003
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Outline

• Motivation
• Status Quo
• New Insights
• Design Gap Example
• Traversing the Gap
• Best Modeling Practices Example Notation
• Conclusions
• Future Work

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Motivation

• Build the largest and fastest switch so far we
  could not build it

• Straightforward evolution not cost-effective,
  sub-optimal
• Incremental changes and invalid assumptions
• Disruptive change fresh concepts required
• Riskful and time-consuming
• Develop methodology

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Status Quo
synthesis
analysis
Implementation

• Single large specification contains all system
  aspects (time consuming)
• Analysis and synthesis on single specification
• Current design flow not suitable for disruptive
  changes

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New Insights
analytical performance protocols sizings test
cases
collection of models
conceptanalysis
DESIGN GAP
synthesis
analysis
Implementation

• Separate concept analysis from synthesis
• Collection of models for different aspects
• Problem you cant make a switch of any of these
  models
• Design gap you cant build a formal tool to
  close it

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Analysis versus Synthesis
Modeling
Description

• Compact and readable (10s..100s lines)
• Separation of concerns a failure is not
  catastrophic
• Do not eliminate optimal solution
• No automatic link to system-level specification

• Complete enough for synthesis
• Rules for transformation and refinement in
  synthesis tools
• consistent specification ? make design decisions
• Not suitable for disruptive changes irreversible

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Design Gap Interpretation Problem

• Models in a Modeling language
• Example analytical Model to calculate
  resequencing delay
• arrangement of language primitives
• appropriate to answer the question(s)
• knowledge of language is not enough to understand
  a Model
• Models require interpretation

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Design Gap Example
weighted_scheduling()() par send_packets(1)()
and send_packets(2)() and ... and
send_packets(N)() rap.
send_packets(queue_number)() packet queues
giveNext(queue_number) delay (1/weights
getWeight(queue_number)) out!packet_message(pa
cket) queues remove(packet)
send_packets(queue_number)()
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Model Interpretation
weighted_scheduling()() par send_packets(1)()
and send_packets(2)() and ... and
send_packets(N)() rap.
send_packets(queue_number)() packet queues
giveNext(queue_number) delay (1/weights
getWeight(queue_number)) out!packet_message(pa
cket) queues remove(packet)
send_packets(queue_number)()

• What could go wrong?
• Understanding the language is not enough
• Fixed interpretation for language primitives? No
• choose any appropriate arrangement
• compact models
• faster iterations of concept analysis

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Traversing the GapModeling Patterns

• Inspired by Design Patterns object-oriented
  software design
• Document a recognizable design strategy
• Yielded good implementations in the past
• Discovered by experience
• Easily recognizable
• Robust against changing requirements
• Modeling Patterns
• document best modeling practices
• typical questions, abstractions, interpretations
• improve communication between modeler and
  designer
• prevent wrong interpretation (or guessing) by
  designers
• prevent costly design iterations

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Link-Level Flow Control Pattern
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Modeling Pattern Notation in UML
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Conclusions

• Disruptive architecture changes require fresh
  concepts riskful and time-consuming
• Disruptive changes existing system-level design
  methods not suitable
• Analyze concepts using various Models, before
  synthesis
• Models lack intended interpretation
• Automatic traversal of the design gap impossible
• Fixed interpretation for modeling primitives is
  not a solution
• Convey models and interpretations with patterns
  structured traversal of the gap
• Patterns improve communication, prevent costly
  design iterations
• UML is suitable to document modeling patterns

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Current/Future Work

• Do case-study to evaluate and discover modeling
  patterns
• Bring more structure into the definitions of
  patterns
• Development of a template for textual annotation
  in the UML notation
• classification of typical interpretations
• construction of a modeling pattern catalog (for
  complex communication systems)