1. Software Engineering Chapter 6 Software requirements
Ku-Yaw Chang
Assistant Professor Department of Computer Science and Information Engineering
Da-Yeh University

2. Software Requirements
Objectives
Understand the concepts of user requirements and system requirements and why these requirements should be written in different ways
Understand the differences between functional and non-functional software requirements
Understand how requirements may be organized in a software requirements document
Ku-Yaw Chang
Software Requirements

3. Software Requirements
Preamble
Requirements
Descriptions of the services provided by the system and its operational constraints
Requirements engineering (RE)
The process of finding out, analyzing, documenting and checking these services and constraints
Ku-Yaw Chang
Software Requirements

4. Software Requirements
Preamble
Different level of descriptions
User requirements
Statements of what services the system is expected to provide and the constraints under which it must operate
In a natural language plus diagrams
System requirements
Set out the system’s functions, services and operational constraints in detail
Should be precise, also called functional specification
Define exactly what is to be implemented
Ku-Yaw Chang
Software Requirements

5. Software Requirements
Preamble
User requirement definition
1. LIBSYS shall keep track of all data required by copyright licensing agencies in the UK and elsewhere
Ku-Yaw Chang
Software Requirements

6. Software Requirements
Preamble
System requirement definition
1.1 On making a request for a document from LIBSYS, the requestor shall be presented with a form that records details of the user and the request made.
1.2 LIBSYS request forms shall be stored on the system for five years from the date of the request.
1.3 All LIBSYS request forms must be indexed by user, by the name of the material requested and by the supplier of the request.
1.4 LIBSYS shall maintain a log of all requests that have been made to the system.
1.5 For material where authors’ lending rights apply, loan details shall be sent monthly to copyright licensing agencies that have registered with LIBSYS.
Ku-Yaw Chang
Software Requirements

7. Readers of different types of specification
Client managers
System end-users
Client engineers
Contractor managers
System architects
User requirements
System end-users
Client engineers
System architects
Software developers
System
requirements
Ku-Yaw Chang
Software Requirements

8. Software Requirements
Contents
6.1 Functional and non-functional requirements
6.2 User requirements
6.3 System requirements
6.4 Interface specification
6.5 The software requirements document
6.6 Exercises
Ku-Yaw Chang
Software Requirements

9. 6.1 Functional and non-functional requirements
Statements of services
the system should provide
how the system should react to particular inputs
how the system should behave in particular situations
Non-functional requirements
Constraints on the services or functions offered by the system
timing constraints
constraints on the development process, standards, etc.
Domain requirements
From the application domain of the system and that reflect characteristics of that domain
Ku-Yaw Chang
Software Requirements

10. 6.1.1 Functional requirements
Examples for a university library system called LIBSYS
1. The user shall be able to search either all of the initial set of databases or select a subset from it.
2. The system shall provide appropriate viewers for the user to read documents in the document store.
3. Every order shall be allocated a unique identifier (ORDER_ID), which the user shall be able to copy to the account’s permanent storage area.
Ku-Yaw Chang
Software Requirements

11. 6.1.2 Non-functional requirements
Ku-Yaw Chang
Software Requirements

12. Examples of non-functional requirements
Product requirement
8.1 The user interface for LIBSYS shall be implemented as simple HTML without frames or java applets
Organizational requirement
9.3.2 The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCo-SP-STAN-95.
External requirement
10.6 The system shall not disclose any personal information about system users apart from their name and library reference number to the library staff who use the system.
Ku-Yaw Chang
Software Requirements

13. Metrics for specifying non-functional requirements
Ku-Yaw Chang
Software Requirements

14. Software Requirements
6.1.3 Domain requirements
Be derived from the application domain
Not from the specific needs of system users
Reflect fundamentals of the application domain
Examples
There shall be a standard user interface to all databases that shall be based on the Z39.50 standard.
Because of copyright restrictions, some documents must be deleted immediately on arrival. Depending on the user requirements, these documents will either be printed locally on the system server for manual forwarding to the user or routed to a network printer.
Ku-Yaw Chang
Software Requirements

15. Software Requirements
Contents
6.1 Functional and non-functional requirements
6.2 User requirements
6.3 System requirements
6.4 Interface specification
6.5 The software requirements document
6.6 Exercises
Ku-Yaw Chang
Software Requirements

16. Software Requirements
User requirements
Describe the functional and non-functional requirements
Be understandable by system users without detailed technical knowledge
Should
Simple language, simple tables and forms and intuitive diagrams
Should not
Software jargon, structured notations or formal notations, system implementation
Ku-Yaw Chang
Software Requirements

17. Software Requirements
User requirements
Various problems
Lack of clarity
Requirements confusion
Requirements amalgamation
Ku-Yaw Chang
Software Requirements

18. A user requirement for an accounting system in LIBSYS
4.5
LIBSYS shall provide a financial accounting system that maintains records of all payments made by users of the system. System managers may configure this system so that regular users may receive discounted rates.
Ku-Yaw Chang
Software Requirements

19. Software Requirements
Contents
6.1 Functional and non-functional requirements
6.2 User requirements
6.3 System requirements
6.4 Interface specification
6.5 The software requirements document
6.6 Exercises
Ku-Yaw Chang
Software Requirements

20. Software Requirements
Contents
6.1 Functional and non-functional requirements
6.2 User requirements
6.3 System requirements
6.4 Interface specification
6.5 The software requirements document
6.6 Exercises
Ku-Yaw Chang
Software Requirements

21. Software Requirements
Contents
6.1 Functional and non-functional requirements
6.2 User requirements
6.3 System requirements
6.4 Interface specification
6.5 The software requirements document
6.6 Exercises
Ku-Yaw Chang
Software Requirements

22. Software Requirements
Contents
6.1 Functional and non-functional requirements
6.2 User requirements
6.3 System requirements
6.4 Interface specification
6.5 The software requirements document
6.6 Exercises
Ku-Yaw Chang
Software Requirements