User stories are more narrative than either traditional requirements or use cases. They are intended to describe what the user wants to be able to do. Additionally, user stories focus on the value that comes from using the system rather than a detailed specification of what the system should do. User stories are often called a metaphor for the work being done by the system. The purpose is to capture enough that the agile team can estimate the user story and understand it enough to draft a rough design. The story’s details are collaboratively worked during conversations so the user story itself becomes a promise to hold a conversation as the project progresses. User stories are intended as a means to foster collaboration.
Although user stories aren’t agile in and of themselves, they do emphasize collaboration, which makes user stories difficult to use in non-agile projects. I’ve seen teams that had trouble practicing agile end up with user stories that seemed like highly detailed traditional requirements. Over specification can lead to a series of iterations that become mini waterfalls with each phase (analysis, design, code, and, test) becoming an exercise in writing out an inordinate amount of detail. This is counter to the Agile Manifesto’s principle that “the most efficient and effective method of conveying information to and within a development team is face-to-face conversation.”
To sum up the differences: Traditional requirements focus on system operations with a tendency toward detailed system specification; use cases focus on interactions between the user and the system with a similar tendency of detailed specification; and user stories focus on customer value with a built-in imprecision meant to encourage communication.
User Story Example
Search for candidates by role, specialty, and geographic location.
As a candidate search user, I need the ability to search for candidates by specialty so that I can more efficiently refer patients to specialists.
The candidate search mechanism has the ability to enter a role.
The candidate search mechanism has the ability to enter a specialty.
The specialty search will have a list of candidate specialties from which to select.
Searching via the candidate specialty will return a list of matching specialists or a message indicating that there are no matches.
If there are more results than can fit on one page, the system will provide the capability to view the list in pages or sections.
Are user stories better than other types of requirements specification? It depends on the situation, but in a collaborative environment, my experience leads me to say yes.
User stories will not make your project agile, and the lack of them will make it challenging to become agile. However, user stories encourage a number of principles from the Agile Manifesto:
- Welcome changing requirements, even late in development. Agile processes harness change for the customer's competitive advantage.
- Business people and developers must work together daily throughout the project.
- The most efficient and effective method of conveying information to and within a development team is face-to-face conversation.
- Working software is the primary measure of progress.
If you have a decidedly non-agile environment, will user stories help? Again, it depends on the team. If a team is steeped in waterfall or heavy iterative processes and uses the “big requirements up front” approach, that team likely will influence the user stories, turning them into traditional requirements. User stories are somewhat vague and lend themselves to successive refinement; up-front planning and design is not where their forte lies. Detailed specification is often the practice in heavy process controlled environments before coding begins so that the requirements can be used to budget and plan the entire project. That makes the requirements the source of record for the system with very little room for collaboration. User stories (when used as intended by experts like Cohn and Cockburn) are just too loosely formatted to lend themselves to full documentation. If, on the other hand, the team is open to collaboration with the analysts or business owners, and the project sponsors can tolerate change, user stories can help collaboration.