Requirements vs. Specifications in Software? (+ Examples)


This is about requirement vs. specifications in software.

You’ll learn:

  • What a requirement is
  • What a specification is
  • The differences between those two
  • Lots more

So if you want to know this ERP basic, then this article is for you.

Let’s jump right in!

What Is the Difference Between Requirements and Specifications in Software?

If you’re part of a business or project, you’ve probably heard the terms requirements and specifications before. If you’re not tech-savvy, these terms might be confusing.

Why do we need them?

What’s the difference between requirements vs. specifications?

You’ve come to the right place.

This article will tell you what a requirement is, what a specification is, and why people make the distinction.

Let’s get started!

Everything You Wanted to Know About Requirements (But Were Afraid to Ask)

A requirement is a problem that someone or something needs you to resolve. Think of it like this: you’re buying a new table.

You might take into consideration the following when deciding which one to buy:

  • The dimensions (you want it to fit in the room).
  • The purpose (a coffee table doesn’t make for a great dining table).
  • The materials used (maybe you prefer balsam wood over aluminum).
  • The color (a bright red table wouldn’t work in a green room—trust me).

Those are your requirements.

Any table you buy has to meet those criteria. It’s the same concept with software. The requirements inform the design of the software.

Here’s something you might not know (but might have guessed): there are all kinds of requirements.

Let’s take a look at some of them:

Architecturally Significant Requirements

These requirements are ones that shape the architecture of a system.

The word architectural might bring to mind hardware at first.

However, architecturally significant requirements are vital to software, too. 

What can make these requirements tricky is that they can be hard to define. Moreover, you might find them hiding in other requirements. 

It’s tempting to ignore these parts altogether. That, however, would be a grievous mistake. If you don’t fulfill the architecturally significant requirements, you risk running into technical debt. Because you don’t want that, you must take care of these requirements.

What kinds of requirements are architecturally significant? Here are a few:

  • Anything crucial to the business.
  • Anything that is technically problematic.
  • Something unique—something the architecture doesn’t take care of already.
  • Something that, historically, hasn’t worked (or has been difficult) for your stakeholders.

When you’re talking about these requirements, use words the stakeholders understand. Keep it simple; don’t make it too technical.

Business Requirements

These requirements are what you get from talking to people invested in the project. That’s the people who will buy from you, sell for you, and work with you.

Why should you get their input? It’s helpful, that’s why! For instance, it:

  • Makes sure everyone is on the same page vis-à-vis what needs to happen.
  • Gets these other people feeling they’re involved in the project.
  • Gives you a plan of action from a business perspective.
  • Makes the project more likely to succeed.
  • Will save you money on having to fix things down the line.

Business requirements can look like a lot of things. They can involve the raison d’être of the project and glossaries, for instance.

You might not like to hear it, but these requirements can be hard to get together. After all, you’ve got lots of different needs coming together. To simplify things, be sure to:

  • Define your business.
  • Know the scope of your business.
  • Know what your internal aims are.
  • Identify your business’ capabilities.

User Requirements

User requirements are also known as stakeholder requirements. They focus specifically on how a person—the user—interacts with the software. 

Users won’t always know how to express their desires. They might not know what they want, they might not disclose everything, or they might be plain wrong in what they say. It’s imperative that the business analyst nails down everything.

In the end, you’ll want the user(s) to approve the requirements.

User requirements are a bit like architecturally significant requirements. (Indeed, you might find those requirements embedded in user requirements.) It’s tempting to ignore people who seem lost or clueless. Please don’t do it, though! Their input is necessary for overall software health.

System Requirements

System requirements are hardware requirements as they pertain to a software program.

You know how you can’t run iTunes with Windows 95? That’s because iTunes has higher system requirements than Windows 95.

This set of requirements looks at aspects such as the computer’s:

  • Operating system
  • CPU
  • RAM
  • Available device space
  • External media (for instance, CD-ROMs)
  • Media hardware (like sound and graphics cards)

There are two sub-categories of system requirements: minimum and recommended. They’re exactly what they sound like.

Minimum requirements are the absolute least a software needs to run. Recommended requirements are what make for an optimal user experience.

When in doubt, give users the recommended system requirements.

Functional Requirements

Functional—or solution—requirements relate to the behaviors of a system—its functions. They’re things the system has to do. (You’ll see how they contrast with quality-of-service/non-functional requirements in a bit.) 

You construct them out of the following:

  • A specific number and name.
  • A short description of what the function requirement is.
  • The reason behind the function requirement.

How do you find out which behaviors you need? There are a couple of ways. One is to talk with stakeholders and other relevant parties.

The other is to know the policies of your business or organization. Either or both of these will tell you what your software needs to do.

Analysts might also implement use cases to determine which functions get brought into the software. Those instances usually look like this:

  • A stakeholder or a user requests a certain functionality.
  • The relevant engineers work on clarifying the details of the proposed functionality.
  • Analysts implement use cases to certify the proposed requirement.
  • Your team integrates the requirement if it is valid.

Quality-of-service Requirements

Quality-of-service (or non-functional) requirements refer to the holistic properties of a system. If functional requirements are the details, then non-functional requirements are the bigger picture. They are also known as qualities.

There are two types of non-functional requirements:

  • Execution qualities
  • Evolution qualities

Execution qualities are what you see while the software is running. Evolution qualities are what’s at play in the software at all times.

The ability to be used is a type of execution quality.

The ability to be tested is a kind of evolution quality.

There are various non-functional requirements a software can have. They include but are by no means limited to:

  • Whether or not the software is accessible
  • Whether or not it’s adaptable
  • Current capacity
  • Forecast capacity
  • Whether or not it’s certified
  • How efficient it is
  • How effective it is
  • The way users relate to it on an emotional level
  • If it’s safe to use
  • If it’s secure

Implementation Requirements

Implementation requirements are also known as transition requirements. These requirements are temporary. You need them only to get from one state to another.

Regulatory Requirements

Regulation requirements are aspects of the software put in place for regulatory reasons. These regulations may be:

  • Legal in nature (i.e., there because your software must comply with a given law)
  • Contractual in nature
  • Organizational in nature (i.e., there because of your organization’s standards)

What Makes a Good Requirement?

A lot goes into making a requirement good.

The engineering community agrees upon nine universal traits that make for a top-notch requirement:

  • It deals with a single issue
  • No details are left out
  • There is internal consistency
  • It is atomized (that is, you can’t express it as an and statement)
  • The requirement meets all relevant parties’ needs
  • Everything is up-to-date
  • The wording is exact and accessible
  • Everyone knows how necessary the requirement is
  • You know people can put it into action

Specifications: Keeping Everything Together in One Convenient Place

We’ve gone over what requirements are.

Now, it’s time to address specifications.

A specification is a document comprised of requirements.

Let’s go back to our table example from before.

Say you’ve decided on the following requirements:

  • 3 feet by 5.5 feet
  • Dining table
  • Oakwood
  • Dark brown

All of those requirements compiled together form the table specification. 

What’s necessary here is that the requirements be in a document together. Otherwise, you don’t have a specification. You have an amorphous set of requirements.

Why do you need specifications?

You need them to ensure everything is compatible. 

There’s no shortage of elements a specification document might include. For instance, it could have:

  • A title
  • The time the document was last updated
  • The person (or people) who performed the latest update
  • Organizational logos
  • A table of contents
  • Glossaries
  • The M.O. of the specification
  • Methodologies for testing
  • Visual aids
  • Appendices

Just as there are all kinds of requirements, there are a variety of specifications you might use.

Let’s take a look at some of them:

Architectural Specification

An architectural specification outlines the structural nature of your system. More specifically, it will outline the processes the architects are to follow.

The document needs to be understandable to stakeholders and other readers that are not experts. 

Architectural specifications can take any of these shapes:

  • Rough illustrations
  • Written word
  • Schematics

Whatever form they take, these specifications need to address certain matters, including:

  • The function of the architecture
  • How safe the architecture is (or should be)
  • To what extent the architecture is reliable
  • How the architecture is to be delivered

Document Specification

Document specifications are all about the writing of a document. Such specifications can include, among other aspects:

  • How the document is named
  • The formatting
  • Which language(s) is(are) used
  • Legal concerns related to the document
  • The overall look of the document

Formal Specification

Formal specifications are what you use to implement your software. They’re not the implementations themselves. Instead, they are specifications that help you create an implementation.

People don’t use this type of specification very often. A lot of organizations feel formal specifications:

  • Are too time-consuming for what they do.
  • Need a degree of mathematical skills and expertise that the organization does not have.
  • Aren’t sufficiently agile.
  • Don’t detail what the users and stakeholders need of the software.
  • Are too expensive to be worth it.

These concerns may not be valid for your organization. However, if they are, you’ll probably be able to make it without formal specifications.

Functional Specification

Functional specifications outline the behaviors you expect the program to have. These documents help your team know what to expect of the software before further developing it.

Specifically, there are three main aims of a functional specification:

  • Directing the development team in their building processes.
  • Informing the testing team on which ways to test the software.
  • Telling stakeholders what to expect of the final product.

Program Specification

Program specifications are mostly similar to functional specifications. Both of them aim to illustrate the functions of a given software. Some organizations don’t even distinguish between the two. 

When the two are differentiated, however, it’s typically to distinguish formality levels. Whereas functional specifications are more formal, program specifications are informal.

Unlike formal specifications, program specifications don’t require a ton of math expertise. Software developers might look at them as a type of proto-user guide for that reason.

Why on Earth Should I Care About the Difference Between Requirements vs. Specifications?

A requirement is just one aspect of the broader specification. To return to our table example, 3 feet by 5.5 feet is a requirement; 3 by 5.5 foot dark-brown oak dining table is the specification. If you go to the store with only the dimensions, you’ll probably not get everything you want.

In a way, requirements vs. specifications is a misleading binary.

You can’t have specifications without requirements.

You can have requirements without specifications, but good luck getting far without both components. They work in tandem.

Another way to understand it is that requirements are more human than specifications are.

Stakeholders and other relevant humans inform requirements.

Requirements inform specifications. 

Just as you can’t create software without humans, you can’t make specifications without requirements.

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