Tutorial: Design Document

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Tutorial Design Document

• Introduction to Software Engineering
• Fall 2001
• Muhua Li

2
Design process

• System design
• Transformation of the analysis model into a
  system design model
• (Template see textbook page 222)
• Object design
• Refinement of the analysis and system design
  models, identification of new objects
• (Template see textbook page 277)

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System Design

• What we will get from system design?
• A clear description of strategies for building
  the system
• A subsystem decomposition
• A UML deployment diagram representing the
  hardware/software mapping of the system

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System Design Activities (1)

• Defining design goals
• Derived from the nonfunctional requirements
• As guidance for making trade-off decisions
• Performance, dependability, cost, maintenance,
  and end user criteria
• Only a subset of these criteria will be
  simultaneously taken into account

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System Design Activities (2)

• Finding subsystems
• Start from functional requirements
• Also can from use cases keep functionally
  related objects together
• High coherence and low coupling
• Encapsulating

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Subsystem decomposition

• JazzFestServer This subsystem encapsulates the
  main part of the web server, which supplies the
  services to the client side and the operations on
  the show information data. To be a thin server,
  the server only deals with request from the
  client side and retrieves data from the data
  storage
• Tourist Interface This subsystem encapsulates
  the visual user interface in the client side. It
  deals with the interactions of users and request
  operations from the server.

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System Design Activities (3)

• Mapping subsystems to hardware
• Hardware configuration, platform?
• Defining persistent data Stores
• File/RDB/OODB?
• Defining access control
• Designing the global control flow
• Procedure-driven/Event-driven/Thread?
• Identifying boundary conditions
• Examine how the system is started, initialized,
  and shut down. How to deal with exceptions.

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Hardware/software mapping

• The system uses a Client/Server architecture.
  TouristInterface subsystem runs on PCs with the
  web browsers Netscape and Internet Explorer as
  the virtual machines JazzFestServer subsystem
  runs on a PC supplies server service with Windows
  NT as the virtual machine.

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Object Design

• Object design activities
• Service specification
• Goal precise description of each class interface
• Finding missing attributes and operations
• Specifying type signatures and visibility
• Specifying exceptions
• Specifying constraints (invariants,
  pre-conditions, and post-conditions)

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Object design activities cont.

• Component selection
• off-the-shelf components
• Select class libraries and additional components
• Adjust the selected components
• E.g. JFC and Servelt in the example
• Object model restructuring
• Object model optimization

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Notice

• All the processes mentioned before are always
  iterating though the whole design.
• Not only the final design representation, but
  also your design decisions!
• Be concise! Always use references to enhance
  maintainability of the documents.