1. Software Requirements
Software Engineering Methods - CS234321
Software Requirements
By: Eshcar Hilel
Michael Beder
Software Requirements

2. Software Engineering Methods - CS234321
Agenda
Definitions
Quality Gateway
Example: Traffic Violation Reports System
Software Requirements
Software Requirements

3. Software Engineering Methods - CS234321
Definitions
A requirement is something the system is capable of doing or a property that the system must have.
The requirements must be elicited from the clients needs, expectations and constraints before starting to build the product.
Software Requirements
Software Requirements

4. Software Engineering Methods - CS234321
Definitions
The client/customer pays for the development of the product, or buys the product once it is developed (Computer center - traffic department)
Users will ultimately operate the product. (Police officer)
Stakeholder is any entity (not necessarily human) who either affects the system development or is affected by it
Software Requirements
Software Requirements

5. Functional requirements
Software Engineering Methods - CS234321
Functional requirements
Specify what the capability of the system
Actions the product must take
Derived from main goal of the product
Not a quality
Characterized by verbs
Example: TVRS shall automatically connect with the policemen, vehicles and offenders data bases
Software Requirements
Software Requirements

6. Operational requirements
Software Engineering Methods - CS234321
Operational requirements
Defines a behavior the product must have
Usually contains capabilities (functions) applied in a given behavioral context
Frequently is a part of a sequence of actions
Software Requirements
Software Requirements

7. Non-functional requirements
Software Engineering Methods - CS234321
Non-functional requirements
Properties, or qualities, that the system must achieve, while satisfying its operational/functional requirements
Characterized by adjectives
Checklist:Look and feel, Usability, Performance Maintainability and Portability, etc
Example: The interface between the user and the system must have a maximum response time of two seconds
Software Requirements
Software Requirements

8. Requirements Pitfalls
Software Engineering Methods - CS234321
Requirements Pitfalls
Don’t add unnecessary requirements
Writing requirements is a difficult task
Increases complexity
Invest the time in improving / validating the necessary requirements
Never assume the existence of external systems
Must be explicitly required by the client
The main goal is to increase profits
Avoid complex and/or expensive solutions
Software Requirements
Software Requirements

9. Software Engineering Methods - CS234321
Software Requirements
Software Requirements

10. Software Engineering Methods - CS234321
Quality Gateway
Software Requirements

11. Software Engineering Methods - CS234321
Quality Gateway
Examine each requirement before entering the specification:
Completeness
Traceability
Consistency
Ambiguity
Deal only with the problem
Testability
Gold Plating
Software Requirements
Software Requirements

12. Software Engineering Methods - CS234321
Completeness
A requirements document is complete if it includes all of the significant requirements, whether relating to functionality, performance, design constraints or else
Each requirement is a complete and independent
No sections are marked “to be determined” (TBD)
Software Requirements
Software Requirements

13. Software Engineering Methods - CS234321
Traceability
Each requirement should be contained in a single, numbered paragraph so that it may be referred to in other documents:
Backward traceability - implies that we know why every requirement exists
Each requirement explicitly references its source in previous documents
Forward traceability – allocation of requirement to analysis/design elements.
Software Requirements
Software Requirements

14. Software Engineering Methods - CS234321
Consistency
Different terms used for the same object:
F323 and a “policeman details form” might be used to describe the same form.
Logical or temporal faults: “A follows B” in one part, “A and B occur simultaneously” in another.
“TVRS shall support removal of a policeman record from the personal database” vs. “TVRS shall support read-only access to policeman details”.
Software Requirements
Software Requirements

15. Software Engineering Methods - CS234321
Ambiguity
The difficulty of ambiguity stems from the use of natural language which in itself is inherently ambiguous
The requirement should be phrased so that there is one and only one interpretation for it
Requirement statements should be short, explicit, precise and clear
A glossary should be used when a term used in a particular context could have multiple meanings (I.e. “the user”)
Software Requirements
Software Requirements

16. Deal only with the problem
Software Engineering Methods - CS234321
Deal only with the problem
Requirements should state “what” is required at the appropriate system level, not “how”
However, requirements that specify “how" are still legitimate, but are considered as "design constraints"
The more abstract the requirement, the less likely it is to be a solution
Requirements should be understood by the clients as well as the developers
Software Requirements
Software Requirements

17. Software Engineering Methods - CS234321
Testability
A requirements document is testable (verifiable) if and only if every requirement statement in it is testable.
A requirement is testable if and only if there is some finite cost-effective way in which a person or machine can check to see if the software product satisfies that requirement.
sometimes requirements can only be tested using simulation.
Software Requirements
Software Requirements

18. Software Engineering Methods - CS234321
Testable (cont.)
Example of a non-verifiable requirement:
The TVRS shall complete storage of data within a reasonable time of the user confirming a “Save” sequence
Example of a verifiable requirement:
The TVRS shall complete storage of data within 5 seconds of the user confirming a “Save” sequence, 80% of the time
Software Requirements
Software Requirements

19. Software Engineering Methods - CS234321
Gold Plating
The term comes from gold plated bathroom taps.
Example: TVRS will play a piece of classical music during initialization
Does it matter if this requirement is not included?
Sometimes a little gold plating makes a big difference to the acceptance of the product
Software Requirements
Software Requirements

20. TVRS – Traffic Violation Report System
Software Engineering Methods - CS234321
TVRS – Traffic Violation Report System
Request for Proposal
Software Requirements