System Requirements and Functional Requirememts

StackOverflow https://stackoverflow.com/questions/14781849

  •  07-03-2022
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Question

Can you please explain me the difference between system and functional requirements?

In the company that I working for , I perform a business analyst / design role for one of the applications that is responsible for fulfulling and provisioning a service requested by the customer. My deliverable is a design document that comprises of system requirements and functional requirements. We define system requirements to define high level capabilities of the system and define the functional requirements to break down the system requirements into sufficient detail. So an SR can contain 1-N FRs. I was not sure if it is something that is followed across the industry

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Solution 2

In software engineering functional requirements describe what software is supposed to do. System requirements describe what hardware/OS/middleware software should be run on.

OTHER TIPS

According to "System Analysis and Design, Fifth Edition":

A Functional Requirement "relates directly to a process the system has to perform as a part of supporting a user task and/or information it needs to provide as the user is performing a task.”

Based on this definition, a functional requirement describes what functionality should exist in the system to support an activity (task) that the user would like to achieve. It should not be too technical as it serves as an agreement between the system developer and the user on what is expected from the system in terms of functionality. The user should not at any point expect the system to have features or offer functions that are not specified in the functional requirements. Therefore, the functional requirements are determined during the analysis phase of the system development life cycle (SDLC).

A System requirement, on the other hand, is a technical requirement. It is determined during the design phase of the SDLC. The book states that the focus in this phase is on: "the design of the technical system blueprint that will satisfy the system's requirements".

In short, the main differences are:

1. Purpose and target audience: functional requirements are aimed to communicate what is expected from the system from an end user's perspective, whereas system requirements are aimed at clarifying to developers how the system will be implemented in order to deliver the functional requirements.

2. Timing: functional requirements are specified during analysis, whereas system requirements are specified as part of the design phase.

Punter Vicky, I'll be very practical with you: it's almost the same thing. Functional Requirement is a kind of System Requirement, and describes what system must do. May be calculations, technical details, data manipulation and processing and other specific functionality that define what a system is supposed to accomplish. System Requirement has two meanings: 1) hardware/software/etc prerequisites; 2) like Functional Requirement, but maybe used in an abstract way.

There are different ways to look at/define system and functional requirements and all of them just as correct. Your system requirements can define what the system as a whole is required to do and the functional requirements be written for each sub-part of the system to detail how it fulfills system requirements. Besides tracing between the requirements, you would have another "document" that allocates the system requirements to the different sub-systems. I would still treat those functional requirements at a higher level than software requirements.

Punter Vicky, I have been doing requirements for 20+ years and I have found that the definition is different for each company I work for. I would recommend that you ask for some examples of previous documentation from your company.

The previous answers you have received are technically correct. Functional requirement usually illustrates how the system will work with the user and the System requirements will tell you how the system will technically accomplish the functional requirement. Good luck.

Functional requirement addresses "What" and System requirement addresses "How".

A lawn mover should be able to cut the grass: functional. It may use metal blades or plastic to perform cutting function: system.

With phone, one should be able to call: functional. Battery should stay longer to be able to talk: System or Non functional requirement (NFR)

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