use-case-realization

name	use-case-realization
description	Designs object collaborations for use-case scenarios. Use when translating SSD operations and contracts into sequence or communication diagrams with controllers, domain objects, and services.

Use-Case Realization

Overview

Use-case realization shows how software objects collaborate to satisfy a use-case scenario. It is where GRASP decisions become interaction diagrams and design classes.

When to Use

• You have a use-case scenario, SSD, and important operation contracts.
• You need to discover design classes, methods, and collaborations.
• A system operation requires coordinated domain behavior.
• Do not use before black-box requirements and system events are understood.

Language Adaptation

When the implementation language is known, also use Software Design Language Adaptation and read only its matching language reference. Model actual runtime participants such as functions, modules, callables, values, or channels when they own meaningful behavior; do not invent object lifelines for diagram symmetry.

Workflow

1. Select one scenario and operation sequence. Use the SSD as the external event source.
2. Add the controller entry point. Route each system event to a chosen controller.
3. Assign work with GRASP. For every message, decide the receiver by Expert, Creator, Controller, and coupling/cohesion checks.
4. Show object messages in time order. Use sequence diagrams when order matters; communication diagrams when link structure matters.
5. Create objects at the responsible point. Show creation messages where Creator justifies them.
6. Keep persistence and UI secondary. Include infrastructure only when architecturally relevant to the collaboration.
7. Reflect contract postconditions. Ensure the interaction creates, links, and modifies objects required by contracts.
8. Promote discovered classes. Add stable design classes, methods, and associations to the design class diagram.
9. Repeat for extensions. Realize alternate flows that introduce different collaborations or responsibilities.

Output Template

## Use-Case Realization: [Use Case] - [Scenario]

System Operations:
- [operation(parameters)]

Collaborators:
- [Object/Class]: [role]

Interaction Summary:
1. [Controller] receives [system event].
2. [Sender] -> [Receiver]: [message]

Responsibility Notes:
- [Message]: [GRASP rationale]

Design Classes Discovered:
- [Class.operation()]

Red Flags

• The controller does all the work.
• The diagram repeats SSD black-box messages without internal collaboration.
• Messages are invented without reference to contracts or use-case steps.
• Object creation has no Creator rationale.

Verification

• Every system event is handled by an explicit controller operation.
• Contract postconditions are satisfied by the collaboration.
• Message receivers have GRASP-based responsibility rationale.
• New design classes and methods are recorded for the class diagram.
• Important alternate flows are realized or intentionally deferred.