Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake1 Use Case Diagrams What are they? What do they look like? How to develop a Use Case Diagram in Visio Tips and techniques Assignment context

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake2 What are they? The 1 st stage of our OOM lifecycle –One of the many techniques within UML –Used at the Feasibility and early Analysis stages of a project - to specify WHAT the system should do (not How - this comes later) Supported by many software CASE tools Encourage the user to get involved –Provide a catalyst for discussion with users –Easy to do (much easier than data flow diagrams) –Show Processes – users understand this

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake3 What do they look like? Report Sales Review Individual’s Sales Review Regional Sales Salesperson Regional Sales Manager Accounting system Inventory system Watson’s SalesWeb System (From Understanding UML, Harmon & Watson)

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake4 What does the diagram show? Describe the functions-of / processes-within a system - the “Cases” Identify the boundary of a system Identify who and/or what uses the system - the Actors “are used to describe the outwardly visible requirements of a system” Schneider & Winters (2001) “A use case achieves a discrete goal for the user” Fowler with Scott (1997)

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake5 Use Cases - approach Iteration - initially take a broad, top level view, then later add lower level detail (called the Top Down approach) –as your investigation reveals more facts –as you concentrate on specific areas Refinement - enable the Use Cases to evolve by correcting/improving previous iterations Document however little you know, then add to it.

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake6 Example of the Top-down approach Using Visio – done in the tutorial –Program files Office –Visio »Software Development diagrams »Click on UML diagram »Click on Activity Diagrams »Select Use Case Diagram

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake7 Use Cases - format Diagrams are easy to assimilate –Processes in ellipses –Actors as stick-people –Interactions as lines Text descriptions provide detail –Use Case Scripts discussed next week

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake8 Actors Include users and other systems an actor on a diagram = a role –1 person/system may have 1 or more roles (i.e. in different interactions) –1 role may comprise 1 or more people by convention people are on left, systems on right

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake9 Use Cases (Processes) Functions (initially the major ones only) within the system So the name must be a verb NOT departments in the organisation Some processes may be time-triggered system responses and have no actor involved

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake10 Interactions Where some exchange occurs between an actor and a process may be in either direction the detail of the interaction need not be known at this stage can be labelled/named

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake11 Finding the Actors and Use Cases Use appropriate fact-finding techniques (interviewing, questionnaires, observation, document inspection, …) Identify all users, then the processes they initiate or participate in. Identify all external events to which the system must respond, then relate to actors and processes.

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake12 PSPStock ControllerLogistics Provider Tuneswarehouse Sales Order Processing Stock Control Outbound logistics Inbound logistics Customer Example – top level These lines between Use cases are the subject Of week 2

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake13 Example - 2 nd level Sales Order Processing Create Order Update Order Delete Order Find Order CustomerStock Controller Uses Customer

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake14 Summary Questions You have already been given the answers to these…… 1.What is the purpose of a Use Case diagram? 2.Who needs to be involved with use case diagrams? 3.How many levels of diagram can there be? 4.What is the maximum number of use cases on any diagram? 5.What is a Use Case? an Actor? an Interaction? 6.What does the System Boundary tell us? 7.Why bother having a broad, top-level diagram if we are going to add more detail to lower levels?

Staffordshire UNIVERSITY School of Computing Version Jan 08 original by K.Ingram & J.Westlake15 Use Case Tutorial Task 2 Using Visio draw a top level Use Case Diagram, then all the 2 nd level Use Case Diagrams for a Hire Shop renting out building equipment. See HSS website for understanding of what can be hired out at one of their shopsHSS Show your work to the tutor