Design and Implementation Phase

Question 1

Design and Implementation:

Basic Description

Answer 1

The phase at which an executable software system is developed

Consists of several interleaved activities.

Includes Architectural Design and Modeling of system components.

Question 2

Design and Implementation:

Process Stages/Activities

Answer 2

• Define the System Context and Use Cases
  
  • From SRS
• Architectural Design
• Identify principle system objects
• Componente Design
  
  • Develop Design Models
• Interface Design
  
  • Specify Object Interfaces
• Database Design

Question 3

Defining System Context:

Basics

Answer 3

• Create a Context Diagram
• Understand the relationship between the software and it’s external environment/dependencies
• Define/Diagram Use Cases

Question 4

Architectural Design Step

Answer 4

• Once System Context is understood, use this information to design the System Architecture
• Identify major Components and their Interactions
• Organize components into a well defined Architectural Pattern
  
  • MVC, Layered, Client-Server, etc
• The system may be composed of independent subsystems with varying architecture

Question 5

Object Class Identification step

Answer 5

Using the architecture, identify the different object classes that will be needed.

• This can be a difficult process
• It should be approached iteratively, as you are unlikely to get it right immediately
• Use a “grammatical approach”, based on natural language description
• Base identification on tangible things, like hardware
• There is no “magic” formula, depends on:
  
  • skill
  • experience
  • domain knowledge of system designs

Question 6

Developing Design Models

Answer 6

• Design Models show the objects, object classes and relationships between entities
• Two Categories:
  
  • Static Models
  • Dynamic Models
• Specific Models
  
  • Sequence Models
  • State Machine Models

Question 7

Design Models:

Two Categories

Answer 7

Static Models

Describe the static structure of the system in terms of object classes and relationships

Dynamic Models

Describe dynamic interactions between objects

Question 8

Design Models:

Sequence Model

Answer 8

Shows the Sequence of object interactions

• Objects are arranged horizontally across top
• Time is represented vertically (top to bottom)
• Interactions indicated with stylized arrows
  
  • Calls are solid
  • Callbacks/Responses are dashed
• Each object has a Lifeline represented by a vertical dashed line
• The Controlling Object is represented by a thin rectangle along the object’s lifeline while it is in control

Question 9

Design Models:

State Diagram

Answer 9

Used to show how objects respond to different inputs, service requests, etc,

as well as the State Transitions triggered by these requests.

• Useful, high-level models of a system or object’s runtime behavior
• Not usually required for all objects in a system
  
  • Diagramming simple objects adds unnecessary detail to design
• States are represented with Ovals, Transitions with labeled arrows, black circle indicates starting state

Question 10

Interface Specification step

Answer 10

Specifies the interfaces for all the important objects.

• Necessary so that objects and other components can be designed in parallel
  
  • Need to know HOW an object will be used, even before it is implemented
• Objects may have several interfaces:
  
  • Each represents different viewpoints on the methods provided
• The interface defines method names, parameters and return types

Question 11

Definition:

Software Design

Answer 11

A Software Design is a description of the:

• Structure of the software to be implemented
• Data Models and Structures used by the system
• Interfaces between system components
• Algorithms used (sometimes)

Question 12

Three Types of

Design Input

Answer 12

Platform Information

Requirements Specification

Data Description

Question 13

Four Design Outputs

Answer 13

System Architecture

Database Specification

Interface Specification

Component Specification