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CS
Software Requirements Specification (SRS) Template
Items that are intended to stay in as part of your document are in bold ;
explanatory comments are in italic text. Plain text is used where you might
insert wording about your project.
The document in this file is an annotated outline for specifying software
requirements, adapted from the IEEE Guide to Software Requirements
Specifications (Std 830-1993).
Tailor this to your needs, removing explanatory comments as you go along.
Where you decide to omit a section, you might keep the header, but insert a
comment saying why you omit the data.
CS
(Team Number)
(Team Name)
Software Requirements Specification
Document
Version: (n) Date: (mm/dd/yyyy)
- Introduction
- 1.1 Purpose
- 1.2 Scope
- 1.3 Definitions, Acronyms, and Abbreviations.
- 1.4 References
- 1.5 Overview
- The Overall Description
- 2.1 Product Perspective
- 2.1.1 System Interfaces
- 2.1.2 Interfaces
- 2.1.3 Hardware Interfaces
- 2.1.4 Software Interfaces
- 2.1.5 Communications Interfaces
- 2.1.6 Memory Constraints
- 2.1.7 Operations
- 2.1.8 Site Adaptation Requirements
- 2.2 Product Functions
- 2.3 User Characteristics
- 2.4 Constraints
- 2.5 Assumptions and Dependencies
- 2.6 Apportioning of Requirements.
- Specific Requirements
- 3.1 External Interfaces
- 3.2 Functions
- 3.3 Performance Requirements
- 3.4 Logical Database Requirements
- 3.5 Design Constraints
- 3.5.1 Standards Compliance
- 3.6 Software System Attributes
- 3.6.1 Reliability
- 3.6.2 Availability
- 3.6.3 Security
- 3.6.4 Maintainability
- 3.6.5 Portability
- 3.7 Organizing the Specific Requirements
- 3.7.1 System Mode
- 3.7.2 User Class
- 3.7.3 Objects
- 3.7.4 Feature
- 3.7.5 Stimulus
- 7.6 Response
- 3.7.7 Functional Hierarchy
- 3.8 Additional Comments
- Change Management Process
- Document Approvals
- Supporting Information
1. Introduction
The following subsections of the Software Requirements Specifications (SRS) document should provide an overview of the entire SRS. The thing to keep in mind as you write this document is that you are telling what the system must do – so that designers can ultimately build it. Do not use this document for design!!!
1.1 Purpose
Identify the purpose of this SRS and its intended audience. In this subsection, describe the purpose of the particular SRS and specify the intended audience for the SRS.
1.2 Scope
In this subsection: (1) Identify the software product(s) to be produced by name (2) Explain what the software product(s) will, and, if necessary, will not do (3) Describe the application of the software being specified, including relevant benefits, objectives, and goals (4) Be consistent with similar statements in higher-level specifications if they exist This should be an executive-level summary. Do not enumerate the whole requirements list here.
1.3 Definitions, Acronyms, and Abbreviations.
Provide the definitions of all terms, acronyms, and abbreviations required to properly interpret the SRS. This information may be provided by reference to one or more appendices in the SRS or by reference to documents. This information may be provided by reference to an Appendix.
1.4 References
In this subsection: (1) Provide a complete list of all documents referenced elsewhere in the SRS (2) Identify each document by title, report number (if applicable), date, and publishing organization (3) Specify the sources from which the references can be obtained. This information can be provided by reference to an appendix or to another document. If your application uses specific protocols or RFC’s, then reference them here so designers know where to find them.
application that interfaces with the existing employee payroll system, what is the API to that system that designer’s will need to use? 2.1.2 Interfaces Specify: (1) The logical characteristics of each interface between the software product and its users. (2) All the aspects of optimizing the interface with the person who must use the system This is a description of how the system will interact with its users. Is there a GUI, a command line or some other type of interface? Are there special interface requirements? If you are designing for the general student population for instance, what is the impact of ADA (American with Disabilities Act) on your interface? 2.1.3 Hardware Interfaces Specify the logical characteristics of each interface between the software product and the hardware components of the system. This includes configuration characteristics. It also covers such matters as what devices are to be supported, how they are to be supported and protocols. This is not a description of hardware requirements in the sense that “This program must run on a Mac with 64M of RAM”. This section is for detailing the actual hardware devices your application will interact with and control. For instance, if you are controlling X10 type home devices, what is the interface to those devices? Designers should be able to look at this and know what hardware they need to worry about in the design. Many business type applications will have no hardware interfaces. If none, just state “The system has no hardware interface requirements” If you just delete sections that are not applicable, then readers do not know if: a. this does not apply or b. you forgot to include the section in the first place. 2.1.4 Software Interfaces Specify the use of other required software products and interfaces with other application systems. For each required software product, include: (1) Name (2) Mnemonic (3) Specification number (4) Version number (5) Source For each interface, provide: (1) Discussion of the purpose of the interfacing software as related to this software product (2) Definition of the interface in terms of message content and format
Here we document the APIs, versions of software that we do not have to write, but that our system has to use. For instance if your customer uses SQL Server 7 and you are required to use that, then you need to specify i.e. 2.1.4.1 Microsoft SQL Server 7. The system must use SQL Server as its database component. Communication with the DB is through ODBC connections. The system must provide SQL data table definintions to be provided to the company DBA for setup. A key point to remember is that you do NOT want to specify software here that you think would be good to use. This is only for customer-specified systems that you have to interact with. Choosing SQL Server 7 as a DB without a customer requirement is a Design choice, not a requirement. This is a subtle but important point to writing good requirements and not over-constraining the design. 2.1.5 Communications Interfaces Specify the various interfaces to communications such as local network protocols, etc. These are protocols you will need to directly interact with. If you happen to use web services transparently to your application then do not list it here. If you are using a custom protocol to communicate between systems, then document that protocol here so designers know what to design. If it is a standard protocol, you can reference an existing document or RFC. 2.1.6 Memory Constraints Specify any applicable characteristics and limits on primary and secondary memory. Don’t just make up something here. If all the customer’s machines have only 128K of RAM, then your target design has got to come in under 128K so there is an actual requirement. You could also cite market research here for shrink-wrap type applications “Focus groups have determined that our target market has between 256-512M of RAM, therefore the design footprint should not exceed 256M.” If there are no memory constraints, so state. 2.1.7 Operations Specify the normal and special operations required by the user such as: (1) The various modes of operations in the user organization (2) Periods of interactive operations and periods of unattended operations (3) Data processing support functions (4) Backup and recovery operations (Note: This is sometimes specified as part of the User Interfaces section.) If you separate this from the UI stuff earlier, then cover business process type stuff that would impact the design. For instance, if the company brings all their systems down at midnight for data backup that might impact the design. These are all the work tasks that impact the design of an application, but which might not be located in software.
What is it about your potential user base that will impact the design? Their experience and comfort with technology will drive UI design. Other characteristics might actually influence internal design of the system.
2.4 Constraints
Provide a general description of any other items that will limit the developer's options. These can include: (1) Regulatory policies (2) Hardware limitations (for example, signal timing requirements) (3) Interface to other applications (4) Parallel operation (5) Audit functions (6) Control functions (7) Higher-order language requirements (8) Signal handshake protocols (for example, XON-XOFF, ACK-NACK) (9) Reliability requirements (10) Criticality of the application (11) Safety and security considerations This section captures non-functional requirements in the customers language. A more formal presentation of these will occur in section 3.
2.5 Assumptions and Dependencies
List each of the factors that affect the requirements stated in the SRS. These factors are not design constraints on the software but are, rather, any changes to them that can affect the requirements in the SRS. For example, an assumption might be that a specific operating system would be available on the hardware designated for the software product. If, in fact, the operating system were not available, the SRS would then have to change accordingly. This section is catch-all for everything else that might influence the design of the system and that did not fit in any of the categories above.
2.6 Apportioning of Requirements.
Identify requirements that may be delayed until future versions of the system. After you look at the project plan and hours available, you may realize that you just cannot get everything done. This section divides the requirements into different sections for development and delivery. Remember to check with the customer – they should prioritize the requirements and decide what does and does not get done. This can also be useful if you are using an iterative life cycle model to specify which requirements will map to which interation.
3. Specific Requirements
This section contains all the software requirements at a level of detail sufficient to enable designers to design a system to satisfy those requirements, and testers to test that the system satisfies those requirements. Throughout this section, every stated requirement should be externally perceivable by users, operators, or other external systems. These requirements should include at a minimum a description of every input (stimulus) into the system, every output (response) from the system and all functions performed by the system in response to an input or in support of an output. The following principles apply: (1) Specific requirements should be stated with all the characteristics of a good SRS correct unambiguous complete consistent ranked for importance and/or stability verifiable modifiable traceable (2) Specific requirements should be cross-referenced to earlier documents that relate (3) All requirements should be uniquely identifiable (usually via numbering like 3.1.2.3) (4) Careful attention should be given to organizing the requirements to maximize readability (Several alternative organizations are given at end of document) Before examining specific ways of organizing the requirements it is helpful to understand the various items that comprise requirements as described in the following subclasses. This section reiterates section 2, but is for developers not the customer. The customer buys in with section 2, the designers use section 3 to design and build the actual application. Remember this is not design. Do not require specific software packages, etc unless the customer specifically requires them. Avoid over-constraining your design. Use proper terminology: The system shall… A required, must have feature The system should… A desired feature, but may be deferred til later The system may… An optional, nice-to-have feature that may never make it to implementation. Each requirement should be uniquely identified for traceability. Usually, they are numbered 3.1, 3.1.1, 3.1.2.1 etc. Each requirement should also be testable. Avoid imprecise statements like, “The system shall be easy to use” Well no kidding, what does that mean? Avoid “motherhood and apple pie” type statements, “The system shall be developed using good software engineering practice” Avoid examples, This is a specification, a designer should be able to read this spec and build the system without bothering the customer again. Don’t say things like, “The
Formulas for input to output conversion It may be appropriate to partition the functional requirements into sub-functions or sub- processes. This does not imply that the software design will also be partitioned that way.
3.3 Performance Requirements
This subsection specifies both the static and the dynamic numerical requirements placed on the software or on human interaction with the software, as a whole. Static numerical requirements may include: (a) The number of terminals to be supported (b) The number of simultaneous users to be supported (c) Amount and type of information to be handled Static numerical requirements are sometimes identified under a separate section entitled capacity. Dynamic numerical requirements may include, for example, the numbers of transactions and tasks and the amount of data to be processed within certain time periods for both normal and peak workload conditions. All of these requirements should be stated in measurable terms. For example, 95% of the transactions shall be processed in less than 1 second rather than, An operator shall not have to wait for the transaction to complete. (Note: Numerical limits applied to one specific function are normally specified as part of the processing subparagraph description of that function.)
3.4 Logical Database Requirements
This section specifies the logical requirements for any information that is to be placed into a database. This may include: Types of information used by various functions Frequency of use Accessing capabilities Data entities and their relationships Integrity constraints
Data retention requirements If the customer provided you with data models, those can be presented here. ER diagrams (or static class diagrams) can be useful here to show complex data relationships. Remember a diagram is worth a thousand words of confusing text.
3.5 Design Constraints
Specify design constraints that can be imposed by other standards, hardware limitations, etc. 3.5.1 Standards Compliance Specify the requirements derived from existing standards or regulations. They might include: (1) Report format (2) Data naming (3) Accounting procedures (4) Audit Tracing For example, this could specify the requirement for software to trace processing activity. Such traces are needed for some applications to meet minimum regulatory or financial standards. An audit trace requirement may, for example, state that all changes to a payroll database must be recorded in a trace file with before and after values.
3.6 Software System Attributes
There are a number of attributes of software that can serve as requirements. It is important that required attributes by specified so that their achievement can be objectively verified. The following items provide a partial list of examples. These are also known as non-functional requirements or quality attributes. These are characteristics the system must possess, but that pervade (or cross-cut) the design. These requirements have to be testable just like the functional requirements. Its easy to start philosophizing here, but keep it specific. 3.6.1 Reliability Specify the factors required to establish the required reliability of the software system at time of delivery. If you have MTBF requirements, express them here. This doesn’t refer to just having a program that does not crash. This has a specific engineering meaning. 3.6.2 Availability
tradeoff analysis between different non-functional requirements. H/M/L is the relative priority of that non-functional requirement. ID Characteristic H/M/L 1 2 3 4 5 6 7 8 9 10 11 12 1 Correctness 2 Efficiency 3 Flexibility 4 Integrity/Security 5 Interoperability 6 Maintainability 7 Portability 8 Reliability 9 Reusability 10 Testability 11 Usability 12 Availability Definitions of the quality characteristics not defined in the paragraphs above follow.
- Correctness - extent to which program satisfies specifications, fulfills user’s mission objectives
- Efficiency - amount of computing resources and code required to perform function
- Flexibility - effort needed to modify operational program
- Interoperability - effort needed to couple one system with another
- Reliability - extent to which program performs with required precision
- Reusability - extent to which it can be reused in another application
- Testability - effort needed to test to ensure performs as intended
- Usability - effort required to learn, operate, prepare input, and interpret output THE FOLLOWING (3.7) is not really a section, it is talking about how to organize requirements you write in section 3.2. At the end of this template there are a bunch of alternative organizations for section 3.2. Choose the ONE best for the system you are writing the requirements for.
3.7 Organizing the Specific Requirements
For anything but trivial systems the detailed requirements tend to be extensive. For this reason, it is recommended that careful consideration be given to organizing these in a manner optimal for understanding. There is no one optimal organization for all systems. Different classes of systems lend themselves to different organizations of requirements in section 3. Some of these organizations are described in the following subclasses. 3.7.1 System Mode
Some systems behave quite differently depending on the mode of operation. When organizing by mode there are two possible outlines. The choice depends on whether interfaces and performance are dependent on mode. 3.7.2 User Class Some systems provide different sets of functions to different classes of users. 3.7.3 Objects Objects are real-world entities that have a counterpart within the system. Associated with each object is a set of attributes and functions. These functions are also called services, methods, or processes. Note that sets of objects may share attributes and services. These are grouped together as classes. 3.7.4 Feature A feature is an externally desired service by the system that may require a sequence of inputs to effect the desired result. Each feature is generally described in as sequence eof stimulus-response pairs. 3.7.5 Stimulus Some systems can be best organized by describing their functions in terms of stimuli.
3. 7.6 Response Some systems can be best organized by describing their functions in support of the generation of a response. 3.7.7 Functional Hierarchy When none of he above organizational schemes prove helpful, the overall functionality can be organized into a hierarchy of functions organized by either common inputs, common outputs, or common internal data access. Data flow diagrams and data dictionaries can be use dot show the relationships between and among the functions and data.
3.8 Additional Comments
(c) A description of the problems to be solved by the software (d) Special packaging instructions for the code and the media to meet security, export, initial loading, or other requirements When Appendices are included, the SRS should explicitly state whether or not the Appendices are to be considered part of the requirements. Tables on the following pages provide alternate ways to structure section 3 on the specific requirements. You should pick the best one of these to organize section 3 requirements.
Outline for SRS Section 3 Organized by mode: Version 1
- Specific Requirements 3.1 External interface requirements 3.1.1 User interfaces 3.1.2 Hardware interfaces 3.1.3 Software interfaces 3.1.4 Communications interfaces 3.2 Functional requirements 3.2.1 Mode 1 3.2.1.1 Functional requirement 1. ..... 3.2.1.n Functional requirement 1.n 3.2.2 Mode 2 ..... 3.2.m Mode m 3.2.m.1 Functional requirement m. ..... 3.2.m.n Functional requirement m.n 3.3 Performance Requirements 3.4 Design Constraints 3.5 Software system attributes 3.6 Other requirements
