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Software developers are amazing coders, but coding alone doesn't ensure that software meets user requirements. When developers improvise on design and assume that they fully understand what an application should do, the end result almost always involves app fixes and recoding -- a colossal waste of time for developers, users and the business.
For that reason, every software development project cycle must start with gathering requirements. Rapid development approaches, such as Agile, DevOps and CI/CD, can rely on two versatile and informal means to establish software requirements: user stories and use cases.
Agile development depends on requirements, not only to set a broad scope early on, but also to identify and adjust the requirements for each iteration. In a development paradigm where releases can arrive in a matter of hours, it's critical to have the means to gather goals for developers to readily prioritize and implement. Development teams should understand what goes into a user story vs. a use case, when to use one or the other, and how to write both of them properly.
When to select a user story vs. a use case
The two approaches to software requirements offer unique benefits and share some similarities. Apply use cases and user stories individually or together, depending on the project and the needs of the organization.
User stories. A user story provides a short descriptive sentence that outlines the who, what and why of one or a set of software requirements. User stories put context around interactions, which enables developers to focus their efforts on perspectives, features, functionality and results.
Here's a generic format for a user story:
- A (user/item) should be able to (do something) so that an (outcome) can be achieved.
A product manager or product owner often writes the user stories, and also prioritizes product backlog items. Any team member can write a user story, so hone the skill. Here are two simple examples to follow:
- An accountant should be able to sort receipts by amount and date to quickly find desired receipts.
- An application server should cache active data in memory for improved performance.
These statements guide developers and testers toward the final product through simple, fast, actionable statements. Developers read user stories and implement features, add capabilities to existing features or make fixes and changes based on feedback from previous iterations. By design, user story statements are short; they are not intended to fully describe how the software should work.
User stories are not ideal for every software development discussion. While user stories are quick and simple, they are often devoid of technical detail; that leaves developers with no discussion of how to accomplish a task. There is no assessment of relative difficulty, accounting for resources like developer hours, or prioritization of one user story vs. another. Project managers often make these assessments during the planning phase of each iteration.
Use cases. A use case expresses a functional software requirement by describing a behavior or interaction, often in the form of a flow or a dialog. The focus of a use case is on cause and effect, as it usually outlines how a user or item interacts with software, as well as how that system responds to those actions.
Here's a general use case format:
- A user does (A), the system responds (B).
In most use cases, in contrast to user stories, this cause-and-effect relationship includes additional criteria and responses that form a flow or a chain of events, detailing the feature or function of the software. Use case examples can follow a variety of potential formats, including:
- A guest places an order for concierge assistance. The system forwards the request to the concierge. The concierge sends a personal note of confirmation to the guest's email address.
Use cases generally provide more detail and a deeper understanding of functional behaviors to contextualize a software requirement. Use cases help development teams define or discuss user interface designs, database access or query processes, and API communications. Group use cases together to organize them for complex projects.
Because use cases contain more criteria than a user story, they take more time to create and discuss. The formalized nature of use cases vs. user stories might even constrain developers, especially if planning time is at a premium, as is the case in Agile development environments.
Use cases also differ from test cases, which specify the requirements, inputs, variables and expected results of an individual test.
How to approach use cases and user stories
User stories and use cases share some common elements, including the item or user taking an action, the events that should occur in response to that action, and the reason or end result of the action. The difference between a use case and a user story is primarily the level of detail reflected in each approach.
While they have differences, there's no winner in the user story vs. use case comparison, as they're not mutually exclusive. Developers can turn to both approaches on the same project -- even within the same iteration cycle. The choice of format is a matter of suitability for the particular project, situation and level of formality demanded by the business -- even a bit of personal preference.
For example, a software project early in its lifecycle, where vital features and functionality are still emerging, might benefit from emphasis on detailed use cases. As that software project moves into the later stages of its lifecycle, after the team establishes complex functions, simple user stories might provide a greater benefit, as they address smaller, more specific tasks.
Other considerations also come into play when you select a use case or user story, such as the project client or development team cohesion. For example, a software project under development for an industrial or military client demands copious documentation in all phases of the project's lifecycle. In this case, the leader might choose use cases exclusively over user stories, to meet the business' documentation requirements for the client within normal development procedures.
Editor's note: This article was originally written by Yvette Francino in 2010. Stephen Bigelow updated the article in 2019 to add more context for the two terms.
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