CSC 480 Software Engineering

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CSC 480Software Engineering

• OOAD Process

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Topics

• Overview OOAD Process
• The object model
• Identifying classes
• Responsibilities and collaborations
• Hierarchy inheritance and aggregation

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Macro Development Process

• The process can be roughly divided into three
  major phases
• Analysis focusing on what are required
• Design answering the questions of how to fulfill
  the requirements
• Resulting in blueprints that map functional needs
  to program units (interrelated classes)
• Implementation realizing the design with a
  working system

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Down to the Ground-Level
Ideas
High-up in the air
Conceptualization
Needs statement
Analysis
C-reqts
Functional spec (D-reqts)
Design
Prototypes
Design docs
Solid ground
Implementation
System under dev.
System in production
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Analysis Phase

• Specify system needs in a conceptual model
• High-level, with details omitted
• Document system requirement specification (SRS)
• Completeness
• a contract between client and developers
• Consistency without contradiction
• Readability customer developer (C-D-) reqts
• Addressing all shareholders interests
• Testability can be tested against reality

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Requirements Engineering

• There is no clear-cut boundary between phases
• In OOA process, use cases are a powerful means to
  present and organize requirements
• RUP claims to be use-case-driven
• Good for revealing both external and internal
  needs (user and system requirements)
• Can be used for design, implementation, testing,
  and user training purposes

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The Design Phase

• The goal is to find and present a solution
• The key is decomposition
• Interrelated classes class ?responsibilities
  ?collaborations
• Focusing on architecture (key classes
  interfaces), omitting implementation details
• The outcome is system design document (SDD)
• Class diagrams
• Sequence diagrams
• State diagrams

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Design Phase

• Also known as high-level design
• Classes at various levels of abstraction
• Relationships among classes
• Dependency
• Inheritance
• aggregation
• Product design or UI design may be needed
• Story-boarding
• Screen navigation charts

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Implementation Phase

• Better known as the construction phase
• Detail design sub-class level
• Data structures, algorithms
• Coding
• Unit testing
• Gradual integration and repeated system testing
• Deployment

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Object and Class

• An object is characterized by its
• State
• Behavior
• Identity
• A class specifies objects with the same behavior
• An instance of a class is an object that belongs
  to the given class

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Micro Development Process

• Largely driven by the stream of scenarios and
  architectural products
• Identifying classes and objects
• Identifying semantics of classes and objects
• Identifying the relationships among classes and
  objects
• Implementing classes and objects

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Identifying Classes

• A rule of thumb is to look for nouns in SRS
• Class candidates usually fall in following
  categories
• Tangible things
• Agents
• Events and transactions
• Users and roles
• Systems
• System interfaces and devices
• Foundational classes

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Identifying Responsibilities

• Responsibilities can be mapped to a functional
  requirement
• Responsibilities include
• Things an object need to know state
• Operations an object can perform behavior
• Assign a responsibility to exactly one class
• Assign responsibilities as evenly among classes
  as possible

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Identifying Relationships

• Relationship types
• Hierarchical
• Inheritance
• Aggregation
• Association
• Dependency aka collaborations

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Object Collaborations

• An object tends to fulfill its responsibilities
  by collaborating with other objects
• Client-server contract
• Client the object receiving a service
• Server the object providing the service
• Contract the interface definition through which
  a service may be requested
• The client and server roles may change in
  different collaborations