Common Mechanisms of UML

BASIC BEHAVIORAL MODELING II

Use Cases

• Names 
• Actors
• Flows of Events 
• Scenarios 
• Collaborations 
• Organizing Use Cases
• Common Modeling Techniques

Names:

Every use case must have a name to distinguish itself from other use cases such as the simple name and path name

Actors:

• It represents a systematic set of the roles the users play while interacting with the use cases
• An actor exhibits a role when a human, a hardware device, or even if another system plays with a system 
• Actors and use cases are connected by association 

Flows of Control:

• It includes how and when the use case starts and ends 
• It also includes when the use case interacts with the actors and what objects are exchanged, and the basic flow and alternative flows of the behavior 
• The behavior of a use case can be specified by describing a flow of events in text 
• There can be main flow of events and one or more exceptional flow of events 

Example: 

• This use case begins when a customer arrives at a store's register checkout with items to purchase 
• The cashier starts a new sale with the register 
• The system creates a new sale with the register 
• The cashier records the identifier and quantity for each LineItem 
• The system determines description and price of the current item from the product catalogue and adds the item to the running sale. The details and subtotal are displayed 
• On completion of items entry, the cashier indicates to the POST that the sale is complete 
• The system computes the total including the applicable taxes and displays the information 
• To make a payment, the cashier records the 'cash received' amount 
• The system shows the balance due, records the payment and generates a receipt 
• The customer leaves with the items purchased

Scenarios:

• A scenario is a specific sequence of actions that illustrates behavior in a particular condition 
• For each use case, there will be primary scenarios and secondary scenarios 
• For example, when you buy some items at point-of-sale terminal, paying by cash, paying by credit card, paying by cheque are all different scenarios

Collaborations:

Collaborations are society of classes and other elements that work together to implement the behavior of use cases.

Optimizing Use Cases:

• Grouping them in packages
• Specifying generalization, include, and extend relationships among them 

Generalization: 

• The child use case inherits the behavior and meaning of the parent and usual adds/overrides the behavior 

Include relationship: 

• Base use case explicitly incorporates the behavior of another use case at a location specified in the base. 
• Shown as a dependency, stereotyped as include 

Extend relationship: 

• Base use case implicitly incorporates the behavior of another use case at a location specified indirectly by the extending use case 
• Rendered as a dependency, stereotyped as extend