Plutora Blog - IT Governance, Software Development
Non-Functional Requirements: A Guide With Concrete ExamplesReading time 6 minutes
As functional requirements define what a system should do; non-functional requirements describe how efficiently one should function. Non-functional requirements are just as important as functional requirements. And it is important to accurately identify and define these requirements to ensure that your software runs smoothly while providing a good user experience. Avoiding non-functional requirements can cause critical problems that may lead your product to fail.
So how should you manage them?
In this post, I will explain what non-functional requirements are and how Plutora can help you to best manage them.
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What Are Non-Functional Requirements?
Every requirement that is not functional is a non-functional requirement. Non-functional requirements are different from functional requirements insofar as they do not affect the basic functions of a system. If they are excluded, the system will still function on a basic level. Now you may ask, why are these requirements necessary? Their value comes from a better usability. Non-functional requirements describe how efficiently a system should function. They refer to the general qualities that provide a good user experience. And they improve the quality of performance, accuracy, maintenance, auditing, security, error-handling, reliability, scalability, usability, and capacity.
We can further classify non-functional-requirements as operational, revision, and transition requirements.
Operational requirements describe how well the system is performing. When we refer to operational requirements within non-functional requirements, we are talking about accessibility, confidentiality, integrity, safety, usability, security, availability, efficiency, reliability, and suitability.
Revision requirements define how quickly a system solves problems caused by unexpected errors and how efficiently high-priority features can bounce back.
Maintainability, scalability, flexibility, verifiability, and modifiability are classified as revision requirements.
Transition requirements define the capacity of the system to accept its surrounding environment. The users who are involved in the management of a system are most likely to be concerned about them.
These requirements include good reusability, installability, portability, and interoperability.
Examples of Non-Functional Requirements
Non-functional requirements exist in every system. So it’s important that you analyze the system correctly and figure out all the necessary requirements. For example, the practice of eliciting user needs will identify a number of non-functional requirements. The following questions are examples of what you could ask your users to find out what your functional requirements are:
“How long should process X retain its data ?” (Auditing)
“Please elaborate: when do you want to be able to utilize this process?” (Availability)
“Can you tell me how many times you will use this process per hour?” (Performance)
For any particular solution, non-functional requirements are based on product needs and costs.
Most non-functional requirements have a clear definition. Security requirements are an example. They’re critical. This is due to the large amounts of data collected from various sources such as customer relationship management (CRM) tools and social media accounts. Companies that use either or both of these risk becoming vulnerable and exposed to hackers. But the system can run safely by applying reasonable security requirements.
You can, for example, make decisions about who has what kind of rights and permissions to use the system. Users with operator rights only have access to a particular feature. Those with administrator rights, however, have access to everything. You can also decide whether or not a limited number of operators can access customer details or if all of them can. Operator teams that deal with customer segments may or may not be authorized to access customer details that belong to other operator teams.
According to the system design, availability requirements must have a clear definition, especially in cases where many users have different access rights.
Performance requirements determine how well a system should perform and whether or not it meets expectations. A system’s performance is mainly determined by its throughput and response time.
You’ll need to decide how many operators can use the system at the same time. And you may want to ensure that the system returns data as soon as an operator enters a customer’s credentials. Instant results can significantly reduce costs. And one way to achieve this is by implementing fixed time intervals (e.g., one second).
These determine how the system handles user consumption. What is the process limit per day? How long can data be stored?
Finally, reliability requirements. Do operators need data and processes running at all times? If so, this will affect the system costs.
We can determine the above from user needs, but keep in mind that human behavior is dynamic. Ideas, needs, and non-functional requirements change over time, so you’ll need a better understanding of the system requirements and the non-functional requirements.
Here is an example:
Let’s say your system requires fast order processing. At the moment, it takes ten minutes, so customer details should be retrieved ASAP whenever a user enters their name and address. The system needs to be able to validate data and have enough capacity that it can store customer information for six years per financial regulations.
So what you need to do is divide all information into segments to find the non-functional requirements.
- Reduce the order processing time to less than ten minutes. (How much less is another question you should ask.)
- Accept customer data.
- Retrieve customer details ASAP after a user enters their name and address.
- Validate the customer’s details.
After successfully figuring out your non-functional requirements, you should focus your concern on their documentation and management.
How to Manage Non-Functional Requirements
Non-functional requirements can be managed by using what is known as a non-functional requirements document. The purpose of the document is to share necessary information among stakeholders.
The advantage of creating one of these documents is that it acts to verify whether or not work was completed and if what was paid for has been delivered. Furthermore, documentation allows for the management of project scope.
Like many parts of requirements management, the documentation process is not standardized. Documentation has many approaches and involves a number of revisions. This is problematic for project management and increases risk and lowers compliance. However, there is a solution.
Plutora offers a means to build governance and increase compliance. Project managers create a document standard. Then they ensure that compliance criteria are met. Plutora makes this easier by providing a way to do this automatically.
Finding and defining non-functional requirements can be confusing, although you can find some of them by analyzing users’ needs. Whatever you do, never leave them out of your product. You may create something that functions well enough, but if it takes thirty seconds to load while otherwise working perfectly, it will create a terrible user experience that will effectively render it unusable.
You can manage your non-functional requirements using a documentation process along with Plutora. And you can click here to learn more about IT governance and its principles.