Common Mechanisms of UML

Use Case Diagram 

• A use case diagram displays a set of use cases, actors and their relationships 
• Use case diagrams are used 

To model the dynamic aspects of systems 

To model the use case view of a system 

To test the executable systems through forward engineering 

To understand executable systems through reverse engineering

Contents

Use case diagram contains 

• Use cases 
• Actors 
• Dependency, generalization and association relationships 

It may also contain packages or subsystems, used to group elements in a model into larger chunks

Uses

Use case model the static design view of a system, which is used 

• To model the context of a system 
• To model requirements of a system

Common Modeling Techniques

• Modeling the Context of a System
• Modeling the requirements of a System

Modeling the Context of a System 

To model the context of a system: 

• Recognize the actors that use the system by considering the following groups 

Groups that require help from the system to perform their tasks 
Groups that need to execute the system's functions 
Groups that interact with external hardware or other software systems 
Groups that perform secondary functions for administration and maintenance 

• Classify actors that are similar to one another in a generalization/specialization hierarchy 
• Provide a stereotype for each actor where better understanding is required 
• Develop a use case diagram with these actors and specify the paths of communication from each other to the system's use cases

Modeling the Requirements of a System 

To model the requirements of a system: 

• Constitute the framework or the situation of the system by identifying the actors that interact with it 
• Examine the behavior each actor expects or demands the system to provide 
• Name these common behaviors as use cases 
• Factor common behavior into new use cases used by others; factor variant behavior into new use cases that help extend more main line flows 
• Model these use cases, actors, and their relationships in a use case diagram 
• Enhance these use cases and/or the whole system with notes for outlining nonfunctional requirements