1. Lecture 4: Activity Diagrams
CS2341
Lecture 4: Activity Diagrams
Robert Stevens
11/15/2018
CS2341

2. 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

3. 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
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CS2341

4. 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
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CS2341

5. 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

6. 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

7. 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
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8. 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
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9. 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
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10. 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
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11. Basic Flows
Thus:
Wake Up
Eat Breakfast
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12. 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.
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13. Decision points I Wake Up Eat Breakfast Go for a walk [not hungry]
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14. 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
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15. Concurrency II
Goto lecture
Thus
Listen
Write notes
11/15/2018
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16. 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
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17. Signals Thus: Enter pub Recognise rich friend Signal for a drink
Order a drink
Pay for a drink
Enjoy free drink
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18. 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
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19. 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

20. 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
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CS2341

21. 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
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22. 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
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CS2341

23. 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
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24. 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