How to write a functional specification document in 2022

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When you are writing a functional specification, there are certain things that you need to keep in mind. However, you need to remember the basics of how a functional specification should be written. This is a tutorial we will be covering on how to construct a functional specification so that you don’t have any issues when it’s time to develop the product or any application.

Introduction of functional specification

When approaching software development businesses with a project in hand, it’s a good idea to make a list of all requirements. Development teams use it to create a rough estimate of the project and then, once it’s launched for analysis, to identify all needs.

This article will explain why you need a functional specifications document, and it also defines who it is for and how to create one that ensures the success of your project.

How do you write a functional specification
How do you write a functional specification?

What is a functional specification?

A functional specification is a blueprint that helps the development team understand how an application will work, and it describes the user experience step-by-step.SAP Development incorporates a number of WRICEF solutions. In SAP implementation projects, custom developments are made.

Functional specifications are what developers need to know about the features they want to build and why. Concentrating on a single goal allows everyone involved in the process to find common ground.

Functional specifications (or functional specs) are the final blueprint for how a project or application should look and function. It describes the final product’s functionality, user interface, and appearance.
It saves time and productivity by creating a blueprint before the product is developed. This allows programmers to program rather than work out the logic of user experience. This will enable you to manage your clients’ expectations and help you communicate with them.

How to write Functional Specification

Why write an Functional Specification?

The key benefit of creating a Functional Specific is streamlining the development process. Developers who work from the spec should have all their questions answered to begin building the application.
The client approved this spec, and they are building precisely what they expect. There should not be any questions or ambiguities when the spec is complete, and this is why Functional Specs are necessary.

Components of an Functional Specification

  • An overview of the sub-systems (if appropriate).
  • An overview of the major functions/Area.
  • Proposed stages of construction/implementation.
  • A summary of the benefits and drawbacks of the development.
  • Any critical areas are likely to affect the success of the development.
  • Any required changes to work practices. 
  • During the Functional Specification Phase, any critical assumptions were made.
  • A definition of the scope/objectives.
  • Background of the development
  • GAP Analysis


Any assumptions made in the preparation of this document that could prove crucial to the success or failure of the System should be documented. This could include legislative changes, changes in work practices, changes in technical capabilities for hardware and/or software, etc.

Functional description

A narrative overview of the system concepts upon which the specification is based was created during specification preparation (e.g. Online/real-time), System interfaces and future extensions, management information, goals for reducing paperwork or increasing office output, etc.

This diagram depicts the System’s high-level context data flow diagram, which is represented as a single bubble in relation to other automated systems, departmental areas, or external organisations (e.g., banks, solicitors, etc.), and hardware/system software to be used. a clear narrative overview of the System/subsystem, including its purpose and business rules. It also includes event timings.

Data attribute definitions

A data flow diagram for each function of the System/subsystem. Each function is described in narrative form. Cross-references to Input/Output Descriptions should be included where appropriate. The number of inputs/outputs, processes, files, and interfaces required to automate a function must be documented for each function.

Input /Output Description

Each input must include the layout (e.g., screen design) as well as data attributes. Each output should have a layout (e.g., report design, fonts, etc.) and data attributes. Control features (e.g., batching, etc). There are any requirements to maintain a separate audit trail for data additions, deletions, or modifications.

Interfaces to other system

Diagram of the data flow illustrating the System and its interfaces with other automated systems. This narrative describes the likely timing and method of interfacing with each System. Cross-references to the appropriate interface description in input/output description. This document describes any modifications that are required for existing or proposed systems in order to accommodate this interface.

User performance requirement

In terms of simple, intermediate, and complicated transactions, this description describes the Users Online System Performance Criteria. This description describes the Users Batch System Performance Criteria in terms of the timings of updates (e.g. overnight, two-working days, etc.).

This is the strategy that will be used to capture and convert data prior to implementation. It must include topics like whether the System will begin with an empty or partially loaded database, how it will be accomplished, how tables/code lists will be loaded, what fields are required and what validation must be performed, how data will be taken on, etc.

Testing Senarios

  • An overview of the testing strategy to be used to test the Object for both functionality and performance (e.g., whether testing will be done in levels/passes, what functionality will be tested in each level/pass, what performance tests will be conducted and how, whether testing will be done prior to construction completion, etc)
  • The Object Acceptance Criteria and the Acceptance Threshold are described.


Define any System specific standards to be used. For example, naming conventions to be used for files and screens; use of function keys; standards to be used for screens/report headings etc.

What’s the purpose of an application?

This is a basic, but crucial task. It is essential to have a solid understanding of the product before you begin any work. Ascertain that your team and the product’s managers share the same understanding. There will be a lot of debate and discussion at this stage.

What’s is the application suppose to do?

Based on the mission-critical factors, identify the main objectives for this project. There are usually only a few core functionality pieces that make up the majority of the final product. Other smaller items can be added. You must identify those core pieces and make sure they are a priority. You don’t want the smaller pieces to get in your way. But make sure you have a list. It is a good idea to create a list with all the functions that you would like the application to perform, and then rank them according to priority.

Who will be using this application ?

Learn about your audience (i.e. who will be using the product). Understanding your audience is key to understanding how and why they will use the final application. This is also important for defining the scope of work. Create use cases and user personas. User personas can be used to immerse you, the writer, in the world of your users. It enables you to see things through their eyes.

Do you have a precedent for this application ?

Comparing your product to other products can be beneficial. This will make learning easier for you. Analyze your competitors thoroughly. It will not only assist you in becoming faster, but it will also provide you with insight into your competition and a better understanding of how you might achieve your goals.

Functional Specification for Technical perspective

Detailed business logic will be of great help Developers can understand the requirements clearly if they have a clear understanding of the business requirement. A clear understanding of the requirements will reduce turnaround times.

  • Business logic in SAP , the order of transactions is important. All transactions pertaining to the functionality are included. The need in the form of a flow chart or a pictorial representation.
  • If the functional Speciation documents have interrelated content, the reference embed-related FS is not provided.The object’s impact helps the technical team to understand the implications of certain programming practices and the logic used during development
  • Functional jargon is less commonly used. Layman’s language will be helpful terms such as routings, BOMs, inspection lots and transfer orders are frequently used, sometimes inevitably.These cases require adequate documentation and links to help the reader understand.
  • If possible, please provide table names.provide sample data upfront.(Sample data is used to analyse standard transactions and debug them.
  • If formulae are used, each operand must be described in detail
  • Context for business requirmement
  • Methodology to calculate the value .Eg. Formula :- Q=(n1+n2/c) Also, how to calculate their value from SAP tables.
  • Screen shots should show the complete path from the screen to which they were taken.Eg SPRO path Evaluate attributes Instead of just showing the evaluate attribute screen shot,
functional specification
functional specification
  • It’s crucial to break down logic into points so that it’s easy to understand. It’s also helpful to be able to refer to previously written code.
  • Mentioning the end-user (internal/customer) is important.
  • It’s critical to spell out how errors should be handled. This is a common mistake.
  • Any changes in functional specifications must be documented during development. Documentation should be done.
  • It is important to mention authorization checks that are required for program.A description of the proposed system/sub-system/data level security in terms of access.
  • Boundary conditions should be mentioned e.g. Size of forms, number of screens, fonts, barcode sizes, alignments, etc.
  • Expandability -> State Likely expansion needs so that the program developer can keep these in mind when designing it.

An FS author’s assumptions about the functional understanding of a TS author, even basic, can be dangerous!

  • If possible, provide screenshots and configuration & customizing information. This will help developers understand the requirements better. This will help the developer understand the requirement better.For example, how to create a Production Order. Customizing is required for the Dunning procedure.
  • There are details, details, and more details. It’s critical to remember to include as many specifics as possible. Whiteboard discussions can also be incorporated.
  • Printing program -> How printing will be done should be mentioned. E.g. E.g. Separate transaction.
  • Layouts -> If you’re printing on preprinted stationery, the format must be same. It’s always a good idea to have a sample of stationary on hand.
  • LOGO ->should also be included. In FS, it should clearly state any statutory requirements that must be printed.
  • Interfaces-> The preferred method should be listed. You should also indicate relevant BAPIs if applicable.
  • Interfaces/Conversion-> objects The FS should describe conversion/transformation rules when they are imposed by the business
  • Enhancements-> The existing and desired behaviour should be stated explicitly by FS. It should also specify the actions that must be followed to recreate the behaviour. It is best to offer data from test cases.
  • Module Pool/ Users exits ->All screen fields should be listed. It is important to refer to the standard Table fields.
  • Validations.
    • Screen Flow
    • Data flow through the screens.
    • Status Bar options available for all screens
    • User actions
    • Error handling


This section provides a detailed overview of the workflow and the various steps involved in the design process. This information is very useful to the stakeholders as it provides a detailed understanding of the design process and the various stages that are involved in the design cycle. It also provides an insight into the key deliverables that are required at the end of each stage. A functional specification is not just a piece of document to be read and signed off by the stakeholders. It’s a living document that will need to be updated on a frequent basis as the design process progresses. We, therefore, recommend that the functional specification should be updated as the design process moves from one stage to another. Regular review meetings with stakeholders will be required at each level to ensure that the design effort is aligned with their expectations.

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