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A Use Case Specification is a detailed textual document that describes how a specific interaction occurs between an actor and a system. It complements a Use Case Diagram by providing a full breakdown of logic, conditions, paths, and rules.

Why Use It?

This specification helps stakeholders understand exactly how a system should behave in different situations. It also serves as a reference for developers, testers, and business analysts during development and validation.

Example: Use Case Specification for "Place Order"

Use Case Specification: Place Order
Use Case Name	Place Order
Actors	Customer
Summary Description	The customer selects food items, proceeds to checkout, and completes payment to place an order with the restaurant.
Goal	Allow the customer to successfully place a food order and receive confirmation.
Priority	High
Status	Approved
Preconditions	User is logged in Cart has at least one item
Postconditions	Order is saved in the database Restaurant is notified Customer receives confirmation
Basic Path (Main Flow)	Customer clicks on "Checkout" Enters or confirms delivery address Selects payment method Completes payment System displays order confirmation
Alternative Path	Customer uses promo code before payment Customer selects "Cash on Delivery" instead of online payment Order scheduled for a later time instead of immediate delivery
Business Rules	Promo codes are only valid once per user Orders below $10 cannot be placed Cash on delivery is only available for orders under $50
Non-Functional Requirements	System must respond within 3 seconds at checkout Order data must be stored securely System should support 100 concurrent order placements

Field Reference: What Each Field Means

Field	Purpose
Use Case Name	The title of the use case. It should describe a specific system function.
Actors	The people or systems that interact with this use case (e.g., Customer, Admin).
Summary Description	A short overview of what the use case is about and its context in the system.
Goal	What the actor wants to achieve by executing this use case.
Priority	The business importance or urgency of the use case (e.g., High, Medium, Low).
Status	Indicates where the use case is in its lifecycle (e.g., Draft, Approved, Implemented).
Preconditions	Conditions that must be true before the use case can start.
Postconditions	Conditions that must be true after the use case completes.
Basic Path (Main Flow)	The standard sequence of steps the actor follows to achieve the goal.
Alternative Path	Variations or optional flows that may occur under specific conditions.
Business Rules	Constraints or policies that must be enforced in this use case.
Non-Functional Requirements	Performance, security, and scalability requirements relevant to this use case.

Conclusion

A Use Case Specification is essential for capturing the full behavior of a system function. By including flows, rules, and requirements, it reduces ambiguity and ensures that implementation matches business intent.