How do you leverage functional requirements and use cases to support agile and iterative development?

One thing I have found useful is to tie functional requirements to process groups. Process Groups can be organized into different levels, e.g. Level 1 identifies a subject area, level 2 identifies key processes within subject area and level 3 identifies functional activities for the key process. Tying functional requirement to process group provides better visibility into requirements categorization and its coverage for the end product delivery. It also lands full traceability for design, build and testing, which is essential for assessment of completeness of the final product.

Functional requirements describe the behaviour of the system; what it is supposed to do. Features and functions are are both functional requirements. There are also Non Functional Requirements (NFRs) which describe how the system operates. So performance, security, reliability, and usability are all examples of the NFRs for a system.

Adding some of the deeper truths to Umang’s addition. As you and I see eye to eye on the value of this type of categorization of functions ,requirements and traceability. we know and have proven it will in the end provide a better service to the users and stakeholders . It will also increase the longevity overall , unfortunately it’s rare that budget, time and resources align to allow for this type of well thought out architecture. This is also something that interferes terribly with agile incremental build and deploy development methodologies. Simply put one of the resources will not align and corners will be cut. The core of the issue is not with the methodology or the thoroughness of solution design but lies in stakeholders or users…

Functional requirements are crucial for defining the desired behavior and capabilities of a system from a user and stakeholder perspective. These requirements serve as a basis for the system's design and development, helping to ensure that the final solution meets the needs and expectations of those who will use it. Functional requirements can be further categorized into different types, such as user requirements, system requirements, and interface requirements, depending on the aspect of the system they address.

I've found it helpful to establish personas before writing the use cases. Imagining a persona and a day in the life of that persona helped me write more effective use cases.

Use case is real life scenario, often cuts across job functions and departments, written in business language and usually IT system agnostic. Use case can transcends functional activities, process groups and subject areas. It provides basis for cross-functional demos during Sprint reviews. It acts as end-to-end test scenario aiding final product approval.

Use cases are valuable tools for understanding and documenting how a system will be used in the real world. By describing the specific interactions between users and the system, use cases help to identify and clarify the functional requirements and behaviors of the system. This aids in communication between stakeholders, requirements elicitation, and can serve as a foundation for designing and implementing the system. Use cases are often used in conjunction with other requirement gathering and documentation techniques to provide a comprehensive understanding of system functionality.

Functional requirements rolls up to business processes and ultimately to subject areas, loosely aligned to business area or department functioning. Whereas a Use Case can be formulated grounds up, collating requirements from multiple job functions and responsibilities to fulfill a business-wide objective. For example, reconciling a cash account is the accounting department requirement for financial period close, but performing a Cash Reconciliation between a subledger, bank and general ledger is a Use Case involving disbursement, treasury, accounting and financial reporting departments.

I would say, you can develop functional requirements from use case scenarios. To elaborate this better, usually the software engineers (SEs or someone similar) will first develop the use-case diagram and to explain this better, will write use-case scenarios. By analyzing use-case scenarios, we can do a simple verb identification and see whether the function denoted by each verb can become a functional requirement (see if the function has a input, process and output).

Functional requirements can be very granular addressing detailed job functions. Whereas Use Case stiches detailed requirements into a enterprise function, involving multitude of personas performing business tasks in close coordination.

Both functional requirements and use cases serve as a great aid to determine what is must-have and therefore those features and requirements must be prioritised.

In Agile and iterative development environment, functional requirements can be captured as user stories. User story is attached to process groups and subject areas, and identifies the product owner for the story. Product owner in turn, prioritize the backlog for the sprint delivery. On other hand, use case can be used to showcase sprint delivery for user feedback. Use case can cater to one or multiple user stories, addressing underlying detailed functional requirements.

In addition to Sujal S. said, Functional requirements tie to detailed processes within the subject area. Subject areas can help identify system blocks. On other hand, cross-functional Use case can help identify data movement between system blocks to achieve an end-to-end enterprise function.