1 Lecture 5.2.b: Requirements Specifications (IEEE 830) Dr. John MacCarthy UMBC CMSC 615 Fall, 2006

2 Requirements Standards Active DOD Standards : Defense and Program-Unique Specifications Format and Content [MIL-STD-961E, August, 2003] Software Life Cycle Processes [IEEE , May 1998] Software Life Cycle Processes - Life Cycle Data [IEEE , May 1998] Software Life Cycle Processes – Implementation Considerations [IEEE , May 1998] Data Item Descriptions (DIDs) [MIL-STD-963] IEEE Standards : IEEE Guide for Developing of System Requirements Specification [IEEE ] IEEE Recommended Practice for Software Requirements Specifications [ANSI/IEEE ] Cancelled Standards: Software Development and Documentation [MIL-STD-498, May, 1994] [Replaced by IEEE/EIA series] Defense System Software Development [MIL-STD-2167A, December 1994] [Replaced by MIL-STD-498] IEEE Recommended Practice for Software Requirements Specifications [IEEE ] CIS673/IEEE.pdf [Replaced by ANSI/IEE ] CIS673/IEEE.pdf

3 Industry Standard Software Requirements Specifications (SRS) IEEE Std , IEEE Recommended Practices for Software Requirements Specifications. There are 8 different recommended SRS Templates for Section 3 System Mode (2) User Class Objects Features (Services) Stimulus (Input) Functional Hierarchy (Information Flow) Hybrid Response (Output)

4 Considerations for an SRS (4) Nature of the SRS (4.1) Functionality External Interfaces Performance Attributes Design Constraints Environment of the SRS (4.2): Correctly define SW requirements Should not describe design or implementation details Should not impose unnecessary constraints on the SW Characteristics of a good SRS (4.3) Correct Unambiguous Complete Consistent Ranked for importance and/or stability Verifiable Modifiable Traceable

5 Constraints Section Section 2.4 Constraints Regulatory Policies Hardware Limitations Interfaces to Other Applications Parallel Operation Audit Functions Control Functions Higher-Order Language Requirements Signal Handshake Protocols Reliability Requirements Criticality of the Application Safety and Security Considerations

6 Section 3 Structure 3.1 External Interface Requirements User Interfaces Hardware Interfaces Software Interfaces Communications Interfaces 3.2 Functions 3.3 Performance Requirements 3.4 Design Constraints 3.5 SW System Attributes Reliability Availability Security Maintainability Portability 3.6 Other Requirements

7 Section 3 Organized by Mode [1] 3. Specific Requirements 3.1 External Interface Requirements User Interfaces Hardware Interfaces Software Interfaces Communications Interfaces 3.2 Functional Requirements Mode Functional Requirement Functional Requirement Mode 2 …. 3.3 Performance Requirements 3.4 Design Constraints 3.5 SW System Attributes 3.6 Other Requirements

8 Section 3 Organized by Mode [2] 3. Specific Requirements 3.1 Functional Requirements Mode External Interface Requirements User Interfaces Hardware Interfaces Software Interfaces Communications Interfaces Functional Requirements Functional Requirement Functional Requirement Performance Requirements Mode 2 …. 3.2 Design Constraints 3.3 SW System Attributes 3.4 Other Requirements

9 Section 3 Organized by User Class 3. Specific Requirements 3.1 External Interface Requirements User Interfaces Hardware Interfaces Software Interfaces Communications Interfaces 3.2 Functional Requirements User Class Functional Requirement Functional Requirement User Class 2 …. 3.3 Performance Requirements 3.4 Design Constraints 3.5 SW System Attributes 3.6 Other Requirements

10 Section 3 Organized by Object 3. Specific Requirements 3.1 External Interface Requirements User Interfaces Hardware Interfaces Software Interfaces Communications Interfaces 3.2 Class Objects Class Object Attributes Functions (Services, methods) Messages Class Object 2 …. 3.3 Performance Requirements 3.4 Design Constraints 3.5 SW System Attributes 3.6 Other Requirements

11 Other Organizations Section 3 Organized by Feature Section 3 Organized by Stimulus Section 3 Organized by “Functional Hierarchy” Section 3 Multiple Organizations

12 Section 3 Organized by Functional Hierarchy (2) (My Recommendation) 3. Specific Requirements 3.1 External Interface Requirements User Interfaces Hardware Interfaces Software Interfaces (including data) Communications Interfaces (including data) 3.2 Functional Requirements (Statement of Top-Level Function) Function Function Function … Function 1.2 …. 3.3 Performance Requirements 3.4 Design Constraints 3.5 SW System Attributes 3.6 Other Requirements Suggest a Logical Data Model Annex to support data structures addressed in Sections 3.1.3, 3.1.4, and 3.2 Suggested Functional Leaf Node Requirements Format: Paragraph Number “Shall” statement with Function statement Outputs Triggers Inputs Rule Model Performance (Context/Notes) Note: Non-leaf node function is considered accomplished (from a functional perspective) if all its leaf nodes are accomplished Note: Non-leaf node functions may have performance requirements/attributes that are not simply roll-ups of leaf-node performance Note: One may want to specify the scenario(s) that are to be used to verify performance

13 Example Format 3.2.X.Y The system shall [verb phrase]: where the system generates the following outputs:.. where the activity is triggered by the following conditions: … where the activity is provided the following input: … where the activity follows the following business rules: … where process is completed subject to the following performance requirements: … Context/Notes: … 3.X.Y The system shall [verb phrase] where this function consists of the subfunctions that follow where this function is completed subject to the following performance requirements: … Context/Notes: …