SOFTWARE ENGINEERING LECTURE 5

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SOFTWARE ENGINEERING LECTURE 5

• Today- An overview to OO Analysis and OO
  Design- Introduction of Assignment 2.

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THE PROGRAMMING PARADIGM

• The requirements specification should be as
  programming paradigm (such as OO, logic
  programming, etc.) independent as possible.
• However, thats where it stops. The system
  analysis methods and tools are oriented towards a
  programming paradigms (intentionally or not).
• Usually the programming paradigm has been fixed
  before the analysis starts. Reasons for this
  include- expertise in some paradigm,- clients
  demands,- HW/SW platform

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SYSTEM ANALYSIS METHODS

• Analysis and Design are described in Pressmans
  book both for the Object Oriented approach and
  the so called traditional approach (separate
  descriptions for data and processing, procedural
  implementation language).
• Choose a system analysis method, which-
  communicates with the client, - you have tools
  for (no tools, no motivation),- supports your
  programming paradigm (no additional
  complicated transformations are required),-
  you are familiar with (or willing to learn)

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EXAMPLE METHODS

• Data Flow Diagrams
• SA/SA (Structured Analysis/Structured Design)
• Flowcharts
• Object oriented methods
• NIAM
• ER-diagrams
• Other conceptual modelling methods
• Formal methods based on logic

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TOOLS

• Graphical is generally easier to use
• Nowadays the selection of tools has improved
• The tools should support also software design,
  implementation and modification - prefer an
  integrated or a compatible set of tools.

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OO ANALYSIS AND DESIGN

• There are several competing OO methods and OO
  design languages.
• These are also introduced in Pressmans book.
• These methods share common ideas. We try to
  present these general ideas in todays lecture.

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SYSTEM ANALYSIS

• In the analysis phase, we take the requirements
  and produce a model of the system.
• The analysis model of the system describes the
  architecture of the system on a very rough level.
• The analysis model does not describe the
  implementation, but rather the overall structure
  and functionalities of the system.

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OO SYSTEM ANALYSIS

• Object oriented system analysis produces an
  object oriented model of the system.
• The model produced in OO system analysis needs
  not to be directly implementable.
• The understandability and correctness of the
  model are key points in it.

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OO SYSTEM ANALYSIS MODEL

• The main products in the OO system analysis model
  are- A class diagram- Descriptions of the
  classes- Scenarios created for the use cases
• Classes may be divided into categories.
• Re-usable classes may be identified.

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FINDING CANDIDATE CLASSES

• The candidate classes in the analysis model
  understandably come from the requirement
  specification.
• The text in the specification can be analysed to
  find potential classes.
• Generally, a noun in the requirement description
  corresponds to a potential class.
• Adjectives may represent attributes of these
  candidate classes.
• Verbs may represent methods of these candidate
  classes.

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PERFORM OBJECT ANALYSIS

• Identify subclasses and superclasses
• Common attributes and naming may give hints for
  this.
• Identify whole-part structures (aggregations)
• Analyse the domain to identify re-usable classes.
• Divide classes into subsystems.
• Explain the role and motivation for the class.

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BUILD SCENARIOS

• Build a scenario for each use case.
• The objects in the scenarios should be the
  objects identified of the analysis model obtained
  this far.

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METHODS STATE DIAGRAMS

• The scenarios can now be used to identify methods
  for the objects in the analysis model.
• The methods should have some understandable
  description.
• The exceptions in the use cases (if not included
  in the scenarios) can be used to identify further
  methods.
• Identifying the methods may give rise to new
  attributes.
• Based on the identified methods and the
  attributes, it is possible to construct state
  diagrams for the objects.

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FURTHER OBJECT ANALYSIS

• After all these steps, analyse the analysis
  object model further.
• The result should now describe the structure of
  the system to be built.

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OBJECT ORIENTED DESIGN

• Object oriented design should transform the
  analysis model into a model which can be
  implemented.
• Object oriented design contains the following-
  System design- Human interface design- Object
  design- Data management design- Process
  management design control, priority,

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SYSTEM DESIGN

• Divide the analysis model into subsystems
• Identify hardware components
• Identify processes attach to hardware
• Allocate subsystems to processes
• Identify user interface components
• Choose basic strategy for data management
• Make sure that the overall system structure works
  and design a control mechanism for it.

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HUMAN INTERFACE DESIGN

• Specify human interface functionalities
• Perform graphical design

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OBJECT DESIGN

• Transform the object model into something that
  can be implemented.
• Generally, classes will be divided.
• Implementable classes efficiency
  considerations.
• Describe method parameters and functionality.
• Check attributes (generally, more will be added).
• Create versions of the scenarios which use the
  classes obtained in this object design.
• Iterate, until it seems to work.

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DATA MANAGEMENT DESIGN

• Identify persistent data.
• Identify system parameter data.
• Make a storage plan for these- database type-
  database schema/storage plan- efficiency
  considerations