Lecture 4: Activity Diagrams CS2341 Lecture 4: Activity Diagrams Robert Stevens http://www.cs.man.ac.uk/~stevensr 11/15/2018 CS2341

User Requirements and Business Process User requirements interviews conveys (or implies) the main processes within the problem domain Processes are visible from the business viewpoint Are important at all levels of system development The system is a model of the business process 11/15/2018 CS2341

On Processes Processes are problematic too Many are non-deterministic Many are dynamic - they change rapidly They often involve humans Difficult to gather User interface is an important aspect The system model can change the process 11/15/2018 CS2341

Process is... Structured change, i.e. “there is a pattern of events which an observer may recognise across different actual examples of the process” A specific ordering of work activities across time and place … a structure for action. Davenport, 1993 A bundle of goal directed actions that are performed by actors. Bauer et al, 1993 11/15/2018 CS2341

On Processes In general a process should only exist in order to meet some goal, when you identify a process try to identify a quantifiable goal as well Then identify the Roles which are to be played by actors in order to achieve that goal Your interviews have to uncover actors, activities and their performance 11/15/2018 CS2341

Representing Process Many different types of process, both natural (e.g. fossilisation) and artificial (e.g. articulated by some agent to effect a transformation) Notations for capturing models of processes Many different types of representation: narrative, mathematics especially process algebras diagrammatic techniques: DFDs, RADs, UML Activity Diagrams software enactment: Simulations 11/15/2018 CS2341

Process and UML Activity Diagrams designed to be a simplified look at what happens during a process highlights the activities within a process First stage in capturing what the system will model Embarking on a progression from real world to system world 11/15/2018 CS2341

Activity Diagrams Are an extension of state diagrams State diagrams highlight states and represent activities as arrows between states Activity diagrams highlight activities Need to represent: Indicate start and end; Actors and activities Different roles Decisions and transitions Branches and concurrency 11/15/2018 CS2341

Activity Diagrams I Each activity is represented by a rounded rectangle The processing within an activity completes and then an automatic transition to the next activity occurs. Activity 1 11/15/2018 CS2341

Activity Diagrams II An arrow represents the transition from one activity to the next. The starting point of an activity diagram is represented by a filled-in circle. The end point is represented by a bullseye 11/15/2018 CS2341

Basic Flows Thus: Wake Up Eat Breakfast 11/15/2018 CS2341

Decisions Most processes come to a point where a choice need to be made This is known as a decision point, one path leads to one set of activities, the other to another set. These two paths are mutually exclusive. 11/15/2018 CS2341

Decision points I Wake Up Eat Breakfast Go for a walk [not hungry] 11/15/2018 CS2341

Concurrency Clearly some processes possess concurrent rather than alternative paths Such paths run at the same time (ie are concurrent) and then come together again The split and merge are represented as solid bold horizontal lines 11/15/2018 CS2341

Concurrency II Goto lecture Thus Listen Write notes 11/15/2018 CS2341

Signals During a sequence of activities, it is possible to send a signal. When received, the signal causes activities to take place. The symbol for sending a signal is a convex pentagon The symbol for receiving a signal is a concave polygon Indicate input and output events When received activity takes place Order a drink Buy a drink 11/15/2018 CS2341

Signals Thus: Enter pub Recognise rich friend Signal for a drink Order a drink Pay for a drink Enjoy free drink 11/15/2018 CS2341

Swimlanes I In fact in the previous example we really now need to introduce a new concept The signal has, as a side effect, introduced the notion of two actors in this process the poor student the rich friend We often need this concept of ROLES 11/15/2018 CS2341

Swimlanes II The activity diagram adds this dimension of visualising roles To do this, you separate the diagram into parallel lanes called swimlanes Each swimlane shows the name of the role at the top, and presents the activities of each role. Transitions can take place between swimlanes 11/15/2018 CS2341

Poor student Rich Friend Thus: Swimlanes III Poor student Rich Friend Enter pub Recognise rich friend Call for a drink Order a drink Pay for a drink Enjoy free drink 11/15/2018 CS2341

Activity Diagrams Can be used at all stages of development since they support the notion of hybrid diagrams In general we can use any sensible UML symbol in an activity diagram You can even show an activity diagram for a process inside an object symbol 11/15/2018 CS2341

Activity diagrams We will be using them as a means of capturing the business processes associated with the travel shop A model of the travel shop in the real world But … beware .. We are at this stage only trying to understand the business process We do not want to produce a flowchart of a software algorithm Used to check understanding with the client Use during the user requirements sessions 11/15/2018 CS2341

Scenario Definition User requirements session to establish the context for the system The results of the interactive session with the client are recorded in Activity Diagrams which model: The basic business processes By the use of swimlanes, the main roles that are associated with these processes 11/15/2018 CS2341

What’s been achieved? Nothing so far has referred specifically to the proposed computer system We are understanding the business and the problem domain Only when this is completed shall we turn our attention to gathering system requirements and the envisioning of the proposed computer system Process model to system model 11/15/2018 CS2341