Knowing which requirements document to use at the correct time can mean the difference between a successful project and one that has taken years to complete. For any project to be successful, good requirements documents are key. Below, we’ll go into detail about which requirements documents are most common, and how they can be used to maximize organization and productivity while authoring requirements.
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What are the most common requirements documents?
Of the many different types of requirements documents, three continually stand out as key to any engineering project. The Product Requirements Document (PRD), Functional Requirements Document (FRD), and Software Requirements Document (SRD) or Software Requirements Specification (SRS), are essential tools to any requirements author. Used correctly, these documents can ensure your project is timely, organized and within budget.
Each of these documents is different in content and design and serves a specific purpose for its respective project phase. We’ll cover each of them in detail to help you understand the differences and why each is essential to the requirements authoring process.
What is a Product Requirements Document?
The Product Requirements Document (PRD) describes what a new feature or enhancement should look like and do from the end user’s point-of-view. The PRD is a comprehensive list of all capabilities that are expected for a particular engineering initiative and helps team members such as development and test engineers prepare for their respective workload.
This document should focus on the “what” and not the “how.” The PRD should be implementation neutral. Implementation details are provided later on in the process.
What is usually in a Product Requirements Document?
A solid PRD follows a top-down approach that starts with the overall vision of what the customer wants to accomplish. It should then tie product goals and initiatives to the features required to achieve that vision.
The core content of the PRD should include a high-level vision, specific features to be included, the success criteria and an expected timeframe for delivery.
A typical PRD contains the following:
- Vision, purpose and scope from both a technical and business perspective
- Stakeholder identification
- Market assessment and demographics
- Product overview and use cases
- Specific requirements including
- Functional requirements (e.g. what a product should do)
- Usability requirements
- Technical requirements (e.g. security, network, platform, integration, client)
- Environmental requirements
- Support requirements
- Interaction requirements (e.g. how the product should work with other systems)
- Assumptions, Constraints, and Dependencies
- High-level workflow plans, timelines, and milestones
- Evaluation plan and performance metrics
The PRD is the core guide that is used by subsequent documents in the engineering process. As a logical next step, the PRD can be broken down and analyzed and then translated into a Functional Requirements Document.
Using a template to build your PRD helps ensure the document is clear, compliant and complete. A good PRD defines the value or purpose of a product or specific feature – this PRD template does just that.
What is a Functional Requirements Document?
The purpose of a Functional Requirements Document (FRD) is to define the requirements that are to be implemented as part of the engineering solution. The FRD acts as the technical response to a list of features and functions from the PRD or other business request document.
The functional requirements are where business meets technology. The FRD is the first point of translation for the more technical members of the team, which can include design and test engineers, as well as support personnel.
Where the PRD describes what should be done from an end-user perspective, the FRD helps to translate that into what should be done from a systems perspective. However, an FRD does not include how the system functions will be implemented.
What should be included in a Functional Requirements Document?
The essence of the FRD is to align what you want and need the system to do and what the engineering team is prepared to build. A consensus is usually achieved after the FRD goes through one or more reviews that include the stakeholders.
The typical content of an FRD is:
- Business processes and workflows
- Functional requirements
- Data and integration
- Security requirements
- Data migration & conversion
One popular method of authoring an FRD involves drawing or rendering simple wireframes or accurate, graphically designed UI screenshots. Tools like this help to make it easier for everyone to get on the same page.
After using this downloadable template for an FRD, you’re prepared to take the next step into Software Requirements Documents.
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What is a Software Requirements Document?
The Software Requirements Document (SRD), also known as the Software Requirements Specification (SRS), is the software development team’s blueprint for defining and managing the scope of the project from a systems perspective. It accomplishes that end by outlining the features and intended behaviour of the various software applications.
The SRD also demonstrates that the development team understands what the stakeholders want and that they have a plan for how to implement the ask via a software solution.
What should be included in a Software Requirements Document?
Contrary to popular belief, the SRD does not detail specific solutions with regards to design or technology. The software requirements do, however, need to include enough information to allow the development team to come up with an effective design, without getting into technical jargon so as to alienate the customer. When authoring an SRD, consider using a template, examples of which can be found here.
No matter what methodology your organization follows, the content of the SRD as recommended by the IEEE standards organization should include the following topics:
- Functional Capabilities
- Performance Levels
- Data Structures/Elements
- Constraints and Limitations
Once finalized, the developers and testers can use the SRD to move ahead with coding and test case creation to implement the approved software components of the overall engineering solution.
How can these three documents be used together?
The logical flow for an engineering request is first the creation of a PRD to describe what is being requested from a user perspective. Next, the FRD acts like a bridge between the user perspective and the systems perspective by translating the use cases into operations and activities that the system must do. Finally, an SRD can be written to break the functionality down into manageable parts that the software development team can understand and implement.
How can you get the most out of these requirements documents?
In order to be effective, all of the requirements in each document need to be clear, concise and easily understood by everyone – especially the design and test engineers. There is nothing worse than waiting while a project team spends weeks, months, or even years updating functionality or developing a new product, only to find out that it isn’t what you wanted or needed after all. Money and time wasted because somehow the request did not get translated correctly. Detailed guides such as EARS: The Easy Approach to Requirements Syntax or 21 Top Engineering Tips for Writing an Exceptionally Clear Requirements Document can assist with authoring high-quality requirements.
Using templates for each of the different requirements documents is also an excellent way to ensure consistency across engineering projects, set certain standards for the product and help the project team to learn and grow into a more cohesive and efficient organization.
Ideally, there will also be a core team of people from backgrounds in engineering, design, test, support, sales and marketing, that will be involved for the entire project and review all of the requirements documents to ensure consistency and ensure nothing falls through the cracks. Additional team members such as team leads, architects and subject matter experts (SMEs) can be brought in at different phases of the project to provide their added expertise, as well as a fresh set of eyes.
From time to time when you’ve moved into the actual development phase, it’s good to go back and revisit the PRD, FRD and SRD to make sure that the team has not forgotten key takeaways regarding the specifications.
Ultimately, active engagement and thorough, timely feedback at each step along the way is key to making sure the translation from the customer’s idea to a working product is complete. The three requirements documents described in this article are excellent tools to help document the engineering team’s involvement and commitment to the project’s end goal.
“Product Requirements Document.” Wikipedia, 30 Aug. 2019, en.wikipedia.org/wiki/Product_requirements_document
“Functional specification.” Wikipedia, 24 Aug. 2019, en.wikipedia.org/wiki/Functional_specification
“Software Requirements Specification.” Wikipedia, 9 Oct. 2019, en.wikipedia.org/wiki/Software_requirements_specification
“Product Management: Product Requirements Document.” ProductPlan, www.productplan.com/glossary/product-requirements-document/
Cao, Jerry. “How to Write a Painless Product Requirements Document.” Medium, 14 Jun. 2016, https://medium.com/@uxpin/how-to-write-a-painless-product-requirements-document-508ff6807b4a
“What is a good product requirements document template?” Aha, www.aha.io/roadmapping/guide/requirements-management/what-is-a-good-product-requirements-document-template
Brandenburg, Laura. “What Goes Into a Functional Specification?” Bridging the Gap. www.bridging-the-gap.com/functional-specification/
“Nailing Your Software Requirements Documentation.” Lucidchart, 23 Aug. 2018, www.lucidchart.com/blog/software-requirements-documentation#targetText=A%20software%20requirements%20document%20(also,behavior%20of%20a%20software%20application.