1. System Requirements Specification
Specifying the Specifications

2. Uses of the SRS
Design
Validation
Customer Contract – sometimes

3. When is a requirement not a specification?
Requirement – understanding between customer and supplier
Specification – what the software must do
Requirements that are not in the SRS
Costs
Delivery dates
Acceptance procedures
etc

4. Desired SRS Characteristics
Complete
Consistent
Changeable
Traceable
Course Text – page 516
Mini-Example:
My Dad
versus
My Wife’s Closet

5. IEEE 830
Role of SRS
“The SRS must correctly define all of the software requirements, but no more.”
“The SRS should not describe design, verification, or project management details, except for required design constraints.”

6. Characteristics of a Good SRS
IEEE 830
Characteristics of a Good SRS
Unambiguous
Complete
Verifiable
Consistent
Modifiable
Traceable
Usable during the Operation and Maintenance Phase

7. Ambiguousness – example one
The control total is taken from the last record.
The total is taken from the record at the end of the file.
The total is taken from the latest record.
The total is taken from the previous record.
IEEE

8. Ambiguousness – example two
All customers have the same control field.
All customers have the same value in their control field.
All control fields have the same format.
One control field is issued for all customers.
IEEE

9. Expressing Requirements
Through input/output specs
Use of Representative Examples
Specification of Models
IEEE

10. SRS Table of Contents Introduction General Description
Purpose
Scope
Definitions
References
Overview
General Description
Product Perspective
Product Functions
User Characteristics
General Constraints
Assumptions and Dependencies
Specific Requirements
IEEE

11. 3. Specific Requirements
3.1 Functional Requirements
Func Req 1
Introduction
Inputs
Processing
Outputs
Func Req 2 …
3.2 External Interface Requirements
User Interface
Hardware Interfaces
Software Interfaces
Communication Interfaces
3.3 Performance Requirements
3.4 Design Constraints
Standards Compliance
Hardware Limitations
3.5 Attributes
Security
Maintainability
3.6 Other Requirements
Database
IEEE

12. Non-830-Style Requirements
User stories encourage the team to defer collecting details. An initial place-holding goal-level story ("A Recruiter can post a new job opening") can be written and then replaced with more detailed stories once it becomes important to have the details. This technique makes user stories perfect for time-constrained projects. A team can very quickly write a few dozen stories to give them an overall feel for the system. They can then plunge into the details on a few of the stories and can be coding much sooner than a team that feels compelled to complete an IEEE 830–style software requirements specification
Quote from "Advantages of User Stories for Requirements"
By Mike Cohn

13. Other Specification Techniques
Use Cases
Formal Specification Languages

14. System Modeling Data Model Function and Information Flow Model
Behavior Model

15. Data Modeling Data Objects, Attributes, Relationships
Formatted as Lists or Tables
Entity Relationship Diagrams

16. Functional and Information Flow Modeling
Data Flow Diagrams
compiler
source
code
characters
machine
instructions
object
code
Syntax
Analysis
Semantic
Analysis
characters
tokens
yadda yadda
machine
instructions

17. State Transition Diagram
Behavior Modeling
State Transition Diagram
start
done
file name 1 2 3
save msg
read msg
send
compose 4

18. Next Time…
Midterm Exam