CSC 480 Software Engineering OOAD Process

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

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

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

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-) req’ts Addressing all shareholders interests Testability : can be tested against reality

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

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

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

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

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

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

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

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

Identifying Relationships Relationship types  Hierarchical Inheritance Aggregation  Association Dependency: aka collaborations

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