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S R S S ystem R equirements S pecification Specifying the Specifications.

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Presentation on theme: "S R S S ystem R equirements S pecification Specifying the Specifications."— Presentation transcript:

1 S R S S ystem R equirements S pecification Specifying the Specifications

2 Review from last class Requirements Engineering Tasks 1.Inception 2.Elicitation 3.Elaboration - next brief topic 4.Negotiation 5.Specification - main topic tonight 6.Validation 7.Management

3 Modeling  What are the benefits of building a model?  So, what needs to be modeled?

4 System Modeling  Function & Information Flow Model what we will do with the data  Data Model structure of the information  Behavior Model how we interact with the system

5 Functional and Information Flow Modeling Data Flow Diagrams compiler source code object code characters machine instructions Syntax Analysis characters Semantic Analysis tokens yadda machine instructions DFDs also require a Data Dictionary

6 Data Modeling  Data Objects, Attributes, Relationships Formatted as Lists or Tables  Entity Relationship Diagrams security system sensor monitors enables/disables tests programs is programmed by

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

8 Combining Info Flow & Behavior Use Cases

9 Requirements Engineering Tasks 1.Inception 2.Elicitation 3.Elaboration 4.Negotiation 5.Specification 6.Validation 7.Management

10 Technically Speaking, "requirement" ≠ "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

11 Uses of the SRS  Design  Validation  Customer Contract – rarely

12 IEEE 830 Role of SRS 1. “The SRS must correctly define all of the software requirements, but no more.” 2. “The SRS should not describe design, verification, or project management details, except for required design constraints.”

13 IEEE 830 Characteristics of a Good SRS 1.Unambiguous 2.Complete 3.Verifiable 4.Consistent 5.Modifiable 6.Traceable 7.Usable during the Operation and Maintenance Phase

14 Desired SRS Characteristics  Complete  Consistent  Changeable  Traceable

15 Ambiguousness – example one The control total is taken from the last record. 1. The total is taken from the record at the end of the file. 2. The total is taken from the latest record. 3. The total is taken from the previous record. IEEE 830

16 Ambiguousness – example two All customers have the same control field. 1. All customers have the same value in their control field. 2. All control fields have the same format. 3. One control field is issued for all customers. IEEE 830

17 Ambiguousness – example three  When a user fails to authenticate after a number of times, send a notification to IT.

18 Clear, Complete Unclear  The system shall be able to read updates from MedImg  The system shall be able to provide historical reports Clearer  The system shall be able to import new tumor patient data supplied by MedImg to the radiology management system, for evaluating the tumor to be malignant or benign  The system shall be able to provide patient tumor data for the past five calendar years

19 Expressing Requirements  Through input/output specs aka IEEE 830 Format  Use of Representative Examples  Specification through Models IEEE 830

20 SRS Table of Contents 1.Introduction 1.Purpose 2.Scope 3.Definitions 4.References 5.Overview 2.General Description 1.Product Perspective 2.Product Functions 3.User Characteristics 4.General Constraints 5.Assumptions and Dependencies 3.Specific Requirements IEEE 830

21 3. Specific Requirements 3.1 Functional Requirements 3.1.1 Func Req 1 Introduction Inputs Processing Outputs 3.1.2 Func Req 2 … 3.2 External Interface Requirements 3.2.1 User Interface 3.2.2 Hardware Interfaces 3.2.3 Software Interfaces 3.2.4 Communication Interfaces 3.3 Performance Requirements 3.4 Design Constraints 3.4.1 Standards Compliance 3.4.2 Hardware Limitations 3.5 Attributes 3.5.1 Security 3.5.2 Maintainability 3.6 Other Requirements 3.6.1 Database IEEE 830

22 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

23 Other Specification Techniques  Use Cases  Formal Specification Languages e.g. Petri Nets

24 Next Classes  Risk Analysis and Management  Metrics  Managing the Testing Process

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