CSSE374 Elaboration System sequence diagrams

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Right A typical tool for automating development
using UML Visual Paradigm, Showing an
SSD. From http//www.visual-paradigm.com/ .
CSSE374 Elaboration System sequence diagrams
Steve Chenoweth Day 5, Dec 8, 2008
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Today

• Time to discuss proposed projects with the teams
  who proposed them
• Continue Elaboration
• with SSDs Ch 10
• Tonight Turn-in P0 - A, Prefer a team to work
  for as archs (see Angel drop box). By 1155 PM.
• Tuesday
• Discover the customer team youll work with, as
  archs

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What are SSDs

• System Sequence Diagrams
• Show a particular course of events in a use case,
  highlighting the roles of actors
• Like use cases, they are intended to grow with
  design detail
• Traditionally, end up as test cases, showing
  whats supposed to happen, in order, in very
  specific scenarios

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Whats an SSD look like?
Fig 10.2 SSD for a Process Sale scenario.
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What else looks like SSDs? DFDs?

• Data flow diagrams (DFDs), from 371 kind of
  show similar stuff - connections
• But, in DFDs we didnt worry about the sequence
  of activities!
• With SSDs, thats the main feature!
• DFDs usually at a much higher level
• Just show what-connects-with-what

DFD License branch example from 371.
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What else looks like SSDs? Use Cases?

• Paragraph format not so much rather nebulous

• 2-column format very much
• User does this
• System responds with that

Fig 10.3
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Why bother to draw SSDs?

• Shows flows of events which the system must be a
  part of
• We have to design software to enable these
• Tells precisely what flow of events external
  entities are expecting like with certain
  standards
• Show a specific scenario in a use case
• Leads to understanding of how the software
  actually must work its dynamics

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When to do SSDs

• For the use cases you are about to turn into
  code, in the next iteration
• To highlight the public operations of the system,
  especially (with external actors)

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Keep SSDs Black Box at start

• Like use cases
• Defer design decisions!

Fig 10.4
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SSDs add more in bigger systems

• The flow of each sequence isnt obvious, needs to
  be worked out.
• So, try to decide if your project system will
  make it worthwhile to do detailed artifacts like
  SSDs!

Fig 10.5 SSD for Play Monopoly Game Scenario.