Building Valuable Software Requirement Specifications for Better Software Development

By Kate Eby | July 21, 2017

When developing software, defining requirements before starting development can save time and money. A software requirements document clearly defines everything that the software must accomplish and is a starting base for defining other elements of a product, such as costs and timetables. There is no replacement for good requirements, but each development organization will take a unique approach to the process based on their needs.

In the world of project management, there are two uses of the acronym SRS.  One stands for systems requirements specification - this is a large scale, multi-pronged series of projects in which software requirements specification, the subject here, can play an important part (when the project is related to software development). This article explains the importance of software requirements, how to write effective software requirements, and includes sample software requirement specifications (SRS) documents for guidance.

What Are Software Requirement Specifications?

Software requirement specifications (SRS) articulate, in writing, the needed capabilities, functions, innovations, and constraints of a software development project. A SRS is a document that takes into account the wishes of the stakeholders, all elements (functional and nonfunctional areas), how the software works and interacts with users, and what problems the software will solve. This document then serves as a “parent” document to support the design and development process. The software requirement specifications document is then used to build timetables and estimates of costs for design, testing, validation, and delivery. The document also specifies what to verify during validation and testing, and how to rank functional elements. 
Researching and writing SRS has long been used when preparing for the design, development, and deployment of new software. After extensive input from various technical and non-technical constituents, the document is written to provide a comprehensive, narrative-driven view of what the software will accomplish and how it will behave. One of its main objectives is to foster consensus on what is needed for the new product before actual design, development, and coding begins. 


Why Are Software Requirements Important?

The importance of SRS is realized first from its ability to provide clear communication to the stakeholders on what is being developed and how it will function. Before developers write one line of code, all elements of the product have been specified and articulated through narratives, specifications, visuals such as graphs and tables, and through use cases and real-world scenarios. Developing an SRS is as valuable when used to develop new software in-house as it is in providing an articulate specification document when contracting software development to external development resources. Some of the goals of software requirement specifications include:

  • An accurate description of the scope of work to be completed
  • Clear, easy-to-manage details for software designers and developers
  • Use case scenarios for the testing team
  • Alignment of customer requirements to features
  • Updatable single source of truth for software development
  • Includes input from a variety of stakeholders

Benefits of Great Software Requirements

A strong SRS document can save time in multi-layer communication including user/customer input and feedback, design, validation, testing, and overall user acceptance. Since the main stakeholders have access to the contents of the document and are aware of the agreed upon capabilities and functions, the SRS can also help eliminate duplicated effort and streamline the design and development process. When this rigorous investigation is committed to paper, and the parties involved agree upon the scope and functions, the need for costly redesign or mid-project changes is minimized. The SRS can also save valuable time in communication throughout the development and build process, or when adding new players are to the team. In addition, a comprehensive SRS will: 

  • Increase the accuracy of cost and time estimates
  • Simplify the transition of software from development to production
  • Act as a single source of truth regarding what to include in the software solution
  • Improve communication with stakeholders and customers by sharing portions of the specifications
  • Reduce costly late stage change
  • Document details for future reference
  • Provide users with a documented list of requirements
  • Reduce development effort and task duplication


Who Uses the Software Requirement Specifications?

The SRS document contains narrative elements as well as detailed specification elements. Therefore, even if one technical writer writes the document, it’s important to involve many constituents in planning the SRS. Development of an SRS can include people from marketing and project management, support personnel, product management, customers, and the design and development engineers. Developers, whether full-time or contractors, and testers use the SRS to ensure they are developing the software solution according to the requirements.
Methods for obtaining needed information from stakeholders include questionnaires, interviews, research, meetings, and focus groups. The fact-finding and investigation begin with identifying what to include and the overall goal of the software. It is also beneficial to define what the software will not do and if any industry, corporate policy, or hardware constraints exist. We should note that you don’t craft any real design elements into the document. Instead, the final version will include the appropriate narratives and descriptions, graphs and other visuals, technical specifications, definitions, prioritizing and rating protocols, reference materials, validation and testing, and user scenarios to then build the solution. You integrate any questions regarding capabilities with current capabilities, limitations, business concerns, and costs.  
Rich Graves, Head of Product Management at ServiceAide, closely follows the Agile framework for software development. He finds that the Jobs-to-be-Done way of thinking aids him and his team in building a better product. “Jobs-to-be-Done is a customer-centric way of thinking,” says Graves. “It forces us to think about the user and their end goal. If we can identify with the user and understand their problems, we can write requirements and build a product that is truly innovative. Requirement gathering is not guess work for us since we focus on the target user, their real-life problems, and how we can solve them better than anyone else.”


Best Practices for Writing Software Requirement Specifications

In 2011, the long-used IEEE 29148:1998 standard and template was updated and enhanced and is now known as ISO/IEC/IEEE 29148. This instructional guide provides information for developing a strong SRS document that specifies best practices in five modules. The first three areas describe elements that focus on processes to define scope, using proper references, and setting definitions.  
The 4th module, which is the longest, relates methods for determining the nature, prevailing environment, and general characteristics for developing a good SRS document and plan.  Mastering the articulation of these characteristics can lead to a high-quality and usable SRS.  
The document should be:

  • Correct: A method of analysis that ensures that the software meets the requirements identified.
  • Unambiguous: There is only one interpretation of what the software will be used for and it is communicated in a common language.
  • Complete: There is a representation for all requirements for functionality, performance, design constraints, attributes, or external interfaces.
  • Consistent: Must be in agreement with other documentation, including a systems requirements specification and other documents. 
  • Ranked for Importance and/or Stability: Since all requirements are not of equal weight, you should employ a method to appropriately rank requirements.
  • Verifiable: Use measurable elements and defined terminology to avoid ambiguity.
  • Modifiable: A well-defined organizational structure of the SRS document that avoids redundancies can allow easy adaptation.
  • Traceable: Ability to trace back to the origin of development and move forward to the documents produced from the SRS.

According to Zane Bond, Senior Product Manager at Cisco, “Requirements are at the heart of any new development project. Understanding what is actually required is both a science and an art. Regardless of your development methodology, culture, or delivery types, writing clear and understandable requirements is many times a critical factor in the success of your project. You know you’ve done them right when they are so simple, you wonder why it took so many customer interactions, market analysis, design meetings, and more to write them.”
Bond offers these tips for composing an SRS: 

  • The simpler the requirements, the less you constrain your team into doing things a particular way. There is always a balance between making sure the team has enough context to do the right thing and dictating what is needed through overly specific requirements. This quote from Antoine de Saint-Exupéry comes to mind with requirements: ‘It seems that perfection is attained not when there is nothing more to add, but when there is nothing more to remove.’ Perfection is not really the goal, but the spirit of starting with what you want and then pairing it down to the essentials.
  • Requirements also need to clearly relate to the problem you are solving - who needs this, why do they need this, and more. Knowing the context behind a set of requirements really helps a team make better decisions in the process.
  • The SMART criteria helps you ensure you are not missing key elements, how far you go into this depends on the size of what you are building. Some really small things can be done with minimal requirements, medium to larger items that are strategic require more thorough requirements.


How to Build Software Requirement Specifications

Since 1998, the IEEE template for writing software specification requirements has been used  across numerous industries. Some of the most common templates today use the standard language and incremental set-up found in module five of the ISO/IEC/IEEE 29148 which includes:
i.    Introduction
This area includes scope, purpose, definitions, references, and an overview.
ii.    Overall Description
Document the areas of product perspective and functionality, user characteristics, constraining elements (such as assumptions and dependencies), and apportionment of requirements in this section.
iii.    Specific Requirements (the largest and most important area)
Include all the requirements, functions, interfaces, performance and data requirements, design constraints, security, adjustments needed for site implementation, maintenance, features and systems attributes, priorities, and release plans.
iv.    Supporting Information
Include any Indexes, graphs, appendices, and special instructions not already covered in this section.
Although all areas of the SRS have equal value, in the actual outline it is estimated that you should devote about one-quarter of the time to the Specific Requirements section with emphasis on how to prioritize functions and requirements, validation, and testing for release. 


Steps to Follow In Order to Build Software Requirement Specifications

When building your software requirement specifications you can follow these steps:

  • Start with a sample template: If you have built software requirements in the past, utilizing a pre-existing template is a great place to start. If this is the first time developing software requirements, there are numerous examples and templates that can be found online or through fellow technical writers or product managers, to facilitate the development of a strong and actionable document for any industry.  
  • Identify the writer of the SRS: Although you will have several stakeholders providing input, it is best to have a single technical writer to translate the needs to a language that is understood by the technical staff who will utilize the SRS.
  • Collect requirements from stakeholders: Gather requirements from all stakeholders, both business and the customer. You can gather the information through meetings, interviews, surveys, and questionnaires with customers and business users. You may also choose to perform a market analysis, including a competitive analysis to collect requirements. You can also negotiate and prioritize requirements at this time.


Sample questions to stimulate conversation when gathering requirements

‌ Download Sample Questions to Stimulate Conversation When Gathering Requirements

  • Write the document: Translate and document all of the stakeholder requirements into language that the technical development team can use.
  • Validate requirements: You can align the requirements with the purpose of the software, validating them for practicality, completeness, and clarity.

Words and technical specifications may not be enough to provide clarity. The measured addition of graphics, charts, and other visuals can assist in stakeholder understanding and acceptance. Writing the SRS document is a specific function, so it’s best to have a dedicated writer prepare it (rather than someone who will be directly involved and tasked with the design or development of the software). Since it is generally thought that the writer(s) of the document should be a skilled communicator, employ a dedicated technical writer to craft a final document. Writers, especially technical writers, are trained in research and clarity of communication, in a form that combines narrative and technical writing. The assigned writer should be able to coalesce several different styles, audience input, and objectives into a digestible whole so the various stakeholders have a strong understanding of the software, its functions, and use. Several good suggestions for writing an SRS include:

  • Keep the documentation appropriate to the task at hand  
  • The overall length of the document should match the scope of work, longevity of the product, and the number of users involved 
  • Carefully consider any software or systems that will be integrated or adapted
  • Spend extra time focusing on the most complicated aspects of software functionality 

Since not all functions of the software will have equal weight in the final design and development, there should be an agreed-upon ranking method that includes a value for everything, including the more ambiguous “would be nice to have.” By prioritizing and negotiating, you can communicate the final product functions and descriptions in technical and non-technical terms. All constituents can then participate in acceptance based upon what is and, more importantly, what is not included in the final product.  
As with all software development, the process of building a good software specification requirements document is dependent on the notion of providing opportunities for adaptation. It is estimated that about five percent of the development process will be spent making needed changes. By including a solid adaptation plan into the specifications, it is easier to identify and fix what is often called requirement smells.  Requirement smells, like the more universal code smells, are used to identify design or functional quality weaknesses in the software. Through heuristic as well as subjective means, lurking problems, such as slow responses or the appearance of a bug, can be identified and acted upon earlier rather than discovered later when these smells become a deeper and more costly problem. In some cases, the detection process may be inaccurate and the suspected problem is not a true defect. 

Top 10 Tips for Writing Software Requirements

Writing software requirements takes time, but the payoff is enormous when done correctly. Below are 10 tips that will help you write an effective SRS:

  • Take time to accurately and thoroughly write requirements, especially if it is a large, robust, long-term software solution 
  • The writer should not be the developer, but rather an individual who understands stakeholder needs and the development language
  • Ensure the writer has strong communication skills
  • Include images, graphs, charts, and diagrams to articulate needs
  • Update the SRS as you make changes or re-prioritize requirements
  • Maintain the SRS in an online or shared location that is easy for the team to access
  • Use the requirements for testing and validation
  • Write the SRS for your target audience
  • Ensure the SRS contains everything the development team needs to build the product
  • Link to associated content and documentation

It is often said that you can’t build great products without first having a great plan. This “great plan” document provides significant protections, communications opportunities, and cost- and time-saving benefits for either the design and build or for the purchase of new software. By bringing in the customers, users, technical teams, management and other stakeholders into the process at its earliest inception, communication, budgeting, timelines, and the essential buy-in before initiating the design process can make or break success when you finally deploy the software.


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