Developing a software product without a software requirements specification document is like building without a plan. This article discusses why software requirements specifications are important and provides five effective ways to write the document.
What is a software requirement specification?
A software requirement specification (SRS) is a document that describes the features, behavior, and how a software product, program, or set of programs should perform. As a document ranked in order of importance, an SRS should be correct, complete, consistent, and unambiguous. It should also be verifiable, modifiable, and traceable.
The requirements (functional and non-functional) are usually written in normal language and signed off at the end of the requirements engineering phase.
Often, customers don’t have a clear idea about the intended functionality of the needed software at the start of the project. For this reason, interaction and cooperation between the customer and contractor are usually necessary to understand the customer’s demands. This will help in developing the right SRS for the software.
There are different suggestions for the structure of the software requirements that exist, but no strict rules apply. However, for successful software development, the SRS requirements need to be fulfilled.
Different degrees of formality, details, and methodologies (agile or waterfall) are possible for an SRS document. But the document should include
- A description of the functional requirements
- System features
- Nonfunctional requirements
- Product scope
How does SRS help projects?
Here are ways in which writing an SRS for a project is helpful:
- It’s an important step in starting and launching new software products
- An SRS is a plan of action that provides a complete picture of the project to be done and gives every member of the development and maintenance team a clear roadmap.
- It leaves no ambiguity and prevents deviation from the purposes of the software
- It fine-tunes focus on each requirement and helps in making decisions on the software product.
- It gives an insight into the time it would take to complete the project.
- It provides the outline for the software design and gives the customer and users an idea of the software even while in the initial stages.
- Since the purpose is set at the beginning, SRS helps in saving time and cost
- The agreement between the client and the developer is based on the SRS and also serves as a material for reference and revision in later stages.
- With an SRS, the transfer and use of the software design in another project is easier.
- It lays the groundwork for other teams, such as quality assurance, operations, and maintenance; and makes working with another team seamless.
5 steps to writing the perfect software requirements specification (SRS) document
The following are five steps for writing an SRS document:
- Create an outline to define the purpose of the project
The first step in writing the SRS document is to create an outline. The outline can be created individually or by using an SRS template (there are several SRS templates online). A typical outline has the following sections:
1.2 Intended audience
1.3 Intended use
1.5 Definitions and acronyms
- Overall Description
2.1 User needs
2.2 Assumptions and dependencies
- System Features and Requirements
3.1 Functional requirements
3.2 External interface requirements
3.3 System features
3.4 Nonfunctional requirements
- Define the purpose of the software
Defining the purpose of the product helps to set expectations for the product. For instance, an SRS for an online banking project may have the following purpose:
“The purpose of this document is to present a detailed description of the online banking system. It will explain the purpose and features of the system, the interfaces of the system, what the system will do, the constraints under which it must operate, and how the system will react to external stimuli. “
The purpose of the product should also include:
The intended audience and use
This helps to show who will have access to the SRS in the organization, and how they should use it.
For example, “This document is intended for both the stakeholders and the developers of the system and will be liable for the approval or disapproval of the project by the community of the bank.”
The product scope should be in sync with the overall business goals. It should highlight the goals, objectives, and benefits intended for the product.
The product scope for our example online banking project might be:
“An online banking system will be applicable everywhere where banking exists. It will be a more efficient and easier way to keep a record on systems through which everyone can easily access it according to their rights as compared to the traditional banking system. Every bank will prefer the online banking system instead of the traditional banking system as it contains many useful features and the fastest methods for transactions.”
Definitions and acronyms
At this stage, lay out the definitions of the terms that are being used in the document to ensure a complete understanding by all users.
- Describe what is to be built
Here the product to be built is described. Continuing with our Online Banking project example, the description may take the form of:
“In the traditional system, customers should have to visit the bank branch physically for transactions or some other task. It wastes time. After implementing the online banking system, customers will be able to connect to their accounts through an internet connection. Time usage will be minimized; the task will be done fast instead of waiting for someone else to complete his task. “
Here the user of the product is described, as well as how the product will meet the user’s needs. The development is then done to ease the pains of the user and to allow for seamless adoption of the product.
Assumptions and dependencies
This step lays out all the assumptions made in the SRS. It also takes into consideration all the external factors that the SRS depends on.
- This system will not depend on any other module. It will be web-based, so everyone can independently contact it.
- This project is a stand-alone project, so it will not affect the system where it will be embedded.
- Present details of specific requirements
Although this might feel overwhelming, it’s an important step that helps the development team meet all the requirements. It involves providing as many details as possible about the specific requirements.
Some of the categories to be included in this step are:
Functional requirements are the specific requirements needed for the product to operate. They describe the facilities and services the software needs to perform.
The functional requirements for the example online banking project may look like this:
- Online balance check
- Online shopping opportunity
- Online data entry by the staff
- Updating the data
- Balance transfer
- Checkbook Allotment
External interface requirements
External interface requirements are a type of specific requirement that highlights how the software will interface with other components. These requirements are often necessary for different interfaces, such as:
System features are types of functional requirements needed for a system to function. For example, in the Online Banking project, the steps for the system features could be:
“Customer login > Bank features > Order for an account > Fill the form > Welcome page > Staff login > Check the balance > Transfer balance > Account detail teller”
Depending on the industry, nonfunctional requirements can be as important as functional ones. Nonfunctional requirements include:
- Presentation of the SRS for approval
The final step after completing the SRS is the presentation of the document for review and approval by the stakeholders. It is usually helpful when the presentation is made before all the stakeholders involved in the development, design, and testing stages.
If the feedback from the stakeholder necessitates a modification of the document, those changes and updates are made in the document. Seamless execution of the project is assured when the stakeholders and developers are on the same page.
Although writing an SRS document can seem overwhelming and time-consuming, it’s impossible to exaggerate the importance of the document for a successful software development project.
Without the SRS, a lot of money, time, and effort can go down the drain. Everyone involved in the project—investors, developers, and testers—would not know what is required. Also, the assignment of tasks to a member of the development team will be difficult, if not impossible. All of which would result in an unsatisfactory product for the customer and user.