Book for the slides

1) Systems Analysis and Design

Author: Elias M. Awad

2) Software Engineering, 6th edition

Author: Lan Sommerville

3) Software Engineering

Author: Roger S. Pressman

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System Design It is concerned with how the system functionality is to be provided

by the different components of the system. The following activities are involved:

i. Partition requirements: The requirements are analyzed and collected into groups.

ii. Identify subsystems: Different sub-systems that can individually or collectively meet the requirements are identified.

iii. Assign requirements to sub-systems: The requirements are assigned to subsystems.

iv.Specify sub-system functionality: The specific functions provided by each subsystem are specified.

v. Define sub-system interfaces: It defines the interfaces that are provided and required by each subsystem.

Fig. 2.8 Sommerville p33

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System engineering process- Many different engineering disciplines may be involved in system

engineering.- It involves the following phases:

i) Requirements definition ii) System design iii) Sub-system development iv) System integrationv) System installation vi) System operationvii) System evolution viii) System decommissioning

Fig. 2.6 Sommerville 6th ed.

i) System Requirements definition - It is intended to discover the requirements for the candidate

system as a whole.- The process involves consultation with system customers and

end-users.- It concentrates on deriving three types of requirement:

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1) Abstract functional requirements- The basic functions of the system are defined at an abstract level- Detailed functional requirements specification takes place at the sub-

system level.2) System properties

- These are non-functional emergent system properties, e.g., availability, performance, safety etc.3) Characteristics which the system must not exhibit- It is important to establish a set of overall system objectives

ii) System design: as described in previous slide.

iii) Sub-system development - The subsystems identified during system design are implemented.

iv) System integration - It involves taking independently developed subsystems and putting them

together to make up a complete system.

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v) System installation - During this phase, the system is put into the environment in which it is intended to operate.

vi) System operation - The system is put into operation after it has been installed. - It may involve organizing training sessions for operators and changing the normal work process to make effective use of the new system.

vii) System evolution - Large and complex software must have to evolve to correct errors in the original system requirements, and meet new requirements which have emerged. - The system’s computers are replaced with new faster machines, and may reorganize itself. The external environment of the system may change which may force to change the system.

viii) System decommissioning - It means taking the system out of service after its operational lifetime. - The system engineering activity should anticipate decommissioning and dispose the materials which are damaging to the environment.

System Engineering Process

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Requirements - The description of the services and constraints are the requirements for the system.

Requirements Engineering - It is the process of finding out, analyzing, documenting, and checking these services and constraints is called requirements engineering.

User Requirements - These are statements in a natural language plus diagrams. of what services the system is expected to provide and the constraints under which it must operate.

System Requirements - It set out the system services and constraints in detail. The system requirements document called functional specification should be precise.

Software design specification - It is an abstract description of the software design. The specification add further detail to the system requirements specification.

Software system requirements are:1. Functional requirements:

◦ These are statements of services the system should provide, ◦ how the system should react to particular inputs, and how the system

should behave in particular situations.2. Non-functional requirements: These are constraints on the services or functions offered

by the system, e.g., timing constraints.3. Domain requirements These requirements come from the application domain of the

system and that reflect characteristics of that domain. They may be functional or non-functional requirements.

Functional requirements (Sommerville p100)

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