UML Activity Diagrams and

Modeling • Chap 28, 29 of textbook

• Activity diagram shows sequential and parallel

activities in a process.

• Activity diagrams are useful for modeling

business processes, workflows and complex

algorithms.

• UML state diagrams shows interesting events

and states of an object. It shows how the object

behaves in response to events.

A Typical UML Activity diagram

Activity diagram

• Rich notation to show a sequence of

activities including parallel activities

• Useful for visualizing business workflows

and processes.

• Often better that a fully dressed use case

for depicting complex activities.

• Partitions are useful in seeing multiple

parties and parallel actions

More UML Activity Diagram notation

I could not find the Rake symbol

in MagicDraw. Use the word

(RAKE) for now.

This defines

the sub-

activity

“deliver

order”

Signals – useful to handle events

Activity diagram is

useful in depicting

very complex

processes.

The Rake symbol

and sub activity is

useful for an overall

view

Specifying Behaviour

• Interaction diagrams

– show how object behave in particular

interactions

– do not specify all the possible behaviours of

objects

• Different notation is needed to summarize

the overall behaviour of objects

• UML defines statecharts for this purpose

State machine diagrams and modeling

• Illustrates the interesting events and states of

an object.

• State independent objects always responds

the same way with respect to an event.

• A state dependent object reacts differently to

events based on their state or mode,

determined by the values of some internal

variables.

• A phone is a state dependent object.

• A state machine diagram is useful to depict

state dependent objects.

State-dependent Behaviour

• If an object responds differently to the

same stimulus at different times, this is

modelled by defining a set of states

– an object can be in one state at any time

– the state it is in determines how it responds to

events detected or messages received

– in particular, an event can cause the object to

move from one state to another (a transition)

A simplified view of a simple CD player

• Our CD player has

– A place to hold a CD (which may be empty or have

a CD)

– User interface consisting of

– A load button (opening /closing the place to hold

CD)

– A play button (play a CD – after closing place to

hold CD)

– A stop button (Stop playing)

• This may be modeled by having three states

– The machine is “closed”, “open” or “playing”

States, Events and Transitions

• A simple statechart for a CD player:

Statechart Semantics

• A statechart defines the behaviour of

instances of a given class

• An object is in one active state at a time

• Events may be received at any time

• An event can trigger a transition

– a transition from the active state will fire if it is

labelled with the event just received

• The transition leads to the next active

state

Initial and final states

• Generally we use an initial state (a special

state) that the machine is initially in.

• When the machine stops it is in a final

state (also a special state).

When the machine enters the final state it no

longer responds to any trigger.

Initial and Final States using

magicdraw

• Model the creation and destruction of

objects To put a label

on an arrow,

just select the

label and

start typing

the label.

Non-determinism – avoid using

guard • Sometimes there are two transitions with the

same event label leaving a state. What if there is no CD in the machine and we press play? Nothing should happen. You may show this as follows:

• This is called non-deterministic behaviour – but usually the non-determinism can be removed

by adding more information

Guard Conditions

• Conditions added to events indicate when

a transition can fire For

conditions,

use textbox in

magicdraw

Actions

• Actions are performed when a transition

fires Actions are short self-

contained

processing,

written in plain

English or

pseudo-code,

after the

transition name

with a /. Be

brief!

For actions, use textbox in magicdraw

Entry and exit actions

• Entry and exit actions are properties of

states

– they are performed whenever an object

arrives at or leaves the state, respectively

For each state there

may be an entry

condition, and exit

condition

Activities

• Extended operations that take time to

complete is shown as an activity.

• Activities are performed while the object

is in a state

• unlike actions, they can be interrupted

by new events

Completion Transitions

• If an activity completes uninterrupted it can

trigger a completion transaction

– these are transitions without event labels

Internal Transitions

• Internal transitions do not change state

– and so do not execute entry and exit actions

Creating a Statechart

• It can be hard to identify all necessary

states

• Statecharts can be developed

incrementally

– consider individual sequences of events

received by an object

– these might be specified on interaction

diagrams

– start with a statechart for one interaction

– add states as required by additional

interactions

Ticket Machine

• Consider a ticket machine with two events

– select a ticket type

– enter a coin

• Basic interaction is to select a ticket and

then enter coins

– model this as a ‘linear’ statechart

Refining the Statechart

• This can be improved by adding ‘loops’

– the number of coins entered will vary: entry

will continue until the ticket is paid for

– the whole transaction can be repeated

Adding Another Interaction

• Suppose the user could also enter a coin

before selecting a ticket

• A ‘coin’ transition from the ‘Idle’ state is

needed to handle this event

– this transition can’t go to the ‘Paying for

Ticket’ state as the ticket is not yet selected

– so a new state ‘Inserting Coins’ is required

• The statechart is thus built up step-by-step

Adding a Second Interaction

• If all coins are entered before ticket

selected:

Integrating the Interactions

• In fact, events can occur in any sequence:

Time Events

• Suppose the ticket machine times out after

30 seconds

– we need to fire a transition that is not

triggered by a user-generated event

– UML define time events to handle these

cases For time

events, use

textbox in

magicdraw

Activity States

• Activity states defines periods of time

when the object is carrying out internal

processing

– unlike normal activities, these cannot be

interrupted by external events

– only completion transitions leading from them

– useful for simplifying the structure of complex

statecharts

Returning Change

• Use an activity state to calculate change

Ticket Machine Statechart

A problem to solve

A simple digital watch consists of a display showing hors and minutes

separated by a flashing colon and provides two buttons (A and B) which

enable the display to be updated.

a) To add two to the number of hours displayed, the following actions should

be performed, where button B increments the hours display:

Press A; press B; press B; press A; pressA.

Draw a simple statechart showing precisely this sequence of events.

b) In the above interactions, the hours displayed could be incremented by any

required number and the whole interaction could be repeated as often as

required. Redraw the statechart to incorporate these generalizations.

c) To increment the number of minutes displayed by the watch, button A can

be pressed twice, followed by repeated presses of button B, each of which

increases the minutes displayed by 1. Draw a complete statechart for the

watch, incorporating updates to both hours and minutes displayed.. Give

the states in your statechart meaningful names and add appropriate

actions to any action to any transition labelled ‘press B’.

A problem to solve The watch is subsequently enhanced to incorporate an alarm and the following

interaction sets the time of the alarm:

Press A; press A; press B (repeatedly); press A; press B (repeatedly); press A;

The intention is that the user presses button A in quick succession, (like a double

click with a mouse) to move to the “alarm setting” mode.

A problem to solve

What does this mean?

What does this do?

A problem to solve

Can you read the above diagram ?

A problem to solve