Use Cases, Part I Understanding the Business Dynamics  Understand the business workflow  Identify system support points the system 'use cases'  Basic elements of the Use Case Model

From Business Workflow to System Use Case  What is a Use Case? A use case is a sequence of actions performed by a system that yields an observable result of value to a particular actor.

Use Cases  6 things to know about a Use Case model:  How do I discover Use Cases?  What a Use Case is NOT  Where does ‘Use Case’ fit in the development process?  What are the basic elements of a Use Case Model?  How do I draw a Use Case Model as a diagram?  After the basics, how do I refine the Use Case Model?

How do I discover Use Cases?  two steps:  Business Workflow, drawn as Swimlanes Diagram  Decide the activities in the Business Workflow that call for system support o These will become our initial “use cases.”

Discovering Use Cases -- the Business Workflow

Discovering Use Cases -- deciding system support points

What a Use Case is NOT A Use Case is...  not the workflow between the actors. i.e., it is not the interactions that occur outside the system boundary between “business workers.”  not the interactions between the system components. i.e., interactions that occur within the system boundary ~ the “white- box” view of the system.  not the total set of requirements. i.e., to complete the requirements documentation we need another piece: the "non-behavior" requirements. A Use Case is...  a named description of the users’ (“actors”) interactions with the system. i.e., it reflects a “black-box” view of the system.

Where does the Use Case fit in the development process?  Use Case Diagrams are part of what is used "to model the problem" before we go on to begin to model the solution.  It is a kind of "contract" between customer and developer in a language both can understand and speak.  In the UML, it is a core artifact. the UML calls itself "Use-Case-Driven" o use-cases are developed early-on o use-cases are used throughout the life cycle  In the Unified Process, this is part of the "Requirements Workflow."

What are the basic elements of a Use Case Model? A.What are the parts of a Use Case Model called? B.What does each part look like? C.How do the parts "fit together"?

The Use Case Model – What are its parts called?  There are four core elements of a Use Case Model:  the system (boundary) the set of all use-cases specify a system in terms of its intended functions (functionality). This defines a firm boundary around the system, separating it from the outside world.  the actor someone or something outside the system (boundary) that interacts with the system  the use case a sequence of actions that a system performs that yields an observable result of value to a particular actor.  the request a line of communication between actor and use-case – typically an initiating "transaction." It crosses the system boundary.

What do the parts look like? And how do they fit together? shown as a Use Case Diagram

The Use Case Model  The Use Case diagram is only one part of the Use Case model. Use Case model: a model of the system's intended functions and its environment, consisting of:  Use-Case Diagrams  Use-Case Packages  Actors, each given a:  Actor name  Actor description  Use Cases, each given a:  Use Case name  Use Case summary -- a brief description of: o the nature of what the actor needs (the system) to do o the observable result of value to the actor More detail will be added later

Use-Case Package informal definition: a ‘chunk’ of system functionality. – i.e., a system or sub-system. example: the Customer Loyalty Program processing the new EU-Bid (sub)system UML definition: A use-case package is a collection of use cases, actors, relationships, diagrams, and other packages. It is used to structure the use-case model by dividing it into smaller parts.

Use-Case Package ~ systems & subsystems

Actor informal definition: An actor describes a role that a user plays with respect to the system.  One individual can play several, different roles.  An actor doesn't need to be human (in spite of stick figure icon). o i.e., this includes other (external) systems. example: Branch Manager Mail System Auctioneer UML definition: A actor is someone or something outside the system that interacts with the system.

Actor Discovery Look for ‘users’ that are direct users of the system.  who to include? o all initiating users o significant information providers ?recipients of system outputs (only when useful) Name and describe the actor:  Actor name: o Branch Manager  Actor description: think: "A Branch Manager is..." a manager who has business accountability for one of EU-Rent's vehicle rental locations.

Actor

Use Case informal definition: A use case describes one “case” of how a user can use the system. – i.e., a ‘system service’ that the user can request from the system. example: Register Club Member Order Vehicle Model UML definition: A use case is a sequence of actions performed by a system that yields an observable result of value to a particular actor.

After the basics, how do I refine the Use Case Model? ..