This is an extremely common confusion among many new business analysts. The two techniques sound similar. Both the techniques are used to capture requirements. So, how do these 2 techniques differ from each other? What are their strengths and weaknesses? When should we use "Use case" instead of "User Story"?

Let's discuss. But before we discuss the differences, let's look at both these techniques.

User Story

User stories are a brief textual description, typically 1 or 2 sentences, of functionality that users need from a solution to meet a business objective. A User Story describes the actor (who uses the story), the goal they are trying to accomplish, and any additional information critical to understanding the story's scope.

It is a tool for short-term capture and prioritization of requirements, not for long-term knowledge retention or to provide a detailed analysis. The only detail to be included is information to create an estimate.

User Stories include:

Title

Active-verb phrase describes the activity that a stakeholder wants to carry out with the system.

Statement of value

2 common formats (non-mandatory) are:

"As a <who>, I need to <what>, so that <why>."

As a PM, I should be able to upload an MPP file to sync my project schedule.

"Given...When...Then."

Given that I am a registered user when I visit the website, I should be able to access all the program content.

Conversation

It helps the team to understand the feature and value it will deliver to stakeholders.

Acceptance Criteria

It helps the team to understand what solution needs to provide to deliver value for stakeholders.

Strengths

• Easily understood.
• Prioritizing, estimating, and planning solutions.
• Focuses on value to stakeholders.
• A shared understanding of the domain by collaboration while developing user stories.
• Facilitates rapid delivery and feedback by small, implementable, and testable slices of functionalities.

Limitations

• It can prove to be a challenge due to the lack of detailed specifications.
• Requires context and visibility. It should be supplemented with higher-level analysis and artifacts.
• Regulatory restrictions, or when the organization mandates documentation.

Use Cases and Scenarios

Scenarios and Use Cases describe how actors (a person or a system) interact with a solution to accomplish one or more of that person or system's goals. A Use Case has 2 parts: Use Case Diagram and Use Case Specifications.

Scenarios depict a series of steps performed by actors and solutions to achieve a goal. A use case describes several scenarios in the form of primary and alternate or exception flows.

Use Case Diagram:

Visually depicts the scope of the solution, actors involved, use cases, and relationships between use cases. 

 Associations: Relationships between actors and use cases are known as associations. Two commonly used relationships are:

• Extend: This allows for inserting additional behavior into a use case. Here, the base use case gets extended by the extended use case. The extended use case is optional, and its execution ALWAYS depends on a condition. The point at which extension occurs is called the extension point.

A base use case is complete without an extended use case, whereas an extended use case is incomplete without a base use case.

• Include: Allows base use case to use functionality present in another use case. The included use case is ALWAYS executed. A base use case is incomplete without an included use case.

 Common function is Included and Mandatory. Additional function is Extend and Non-mandatory.

Use Case Specifications

Name

A unique name comprising of a verb and noun.

Goal

Brief description of a successful outcome of a use case from an actor's perspective.

Actors

Any person, system, or event external to the system under design that interacts with that system. Each actor must be given a unique name representing the role they play in system interactions. A particular person may fill roles of multiple actors over time.

A use case is started by an actor, referred to as the primary actor for that use case. Other actors who participate in the use case in a supporting role are called secondary actors. Roles may not match job titles and should NEVER be the names of actual persons.

Trigger

An event (action taken by a primary actor) to initiate a use case.

Flow of events

Set of steps performed by actor and solution during the use case.

Type of flows-

Basic, primary, or main success flow:

The shortest or simplest successful path to achieve an actor's goal.

Alternative flow: Other paths to be followed to achieve an actor's goal.

Exception flow: If a circumstance does not allow an actor to achieve its goal, the use case is considered unsuccessful and is terminated.

For example, in a bank transaction, an ATM machine askings the user to change the amount based on the account balance.

Exception flows are ones where the application fails to achieve the goal, e.g., ATM fails to connect to a bank server.

Post-conditions or guarantees

Any fact that must be true when the use case is complete. It MUST be true for ALL flows. It can be different for successful and unsuccessful outcomes of use case.

Strengths

• Good at clarifying the scope and providing a high-level understanding of requirements.
• Use case specifications makes it easy to understand the functional behavior of a system.

Limitations

• Written at a higher level of abstraction (low level of detail).
• Lack of standardized formats.
• Need analysis to identify include use cases.

Comparing Use Case and User Story

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