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

This defines the sub- activity “deliver order”

I could not find the Rake symbol in MagicDraw. Use the word (RAKE) for now. 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 do?

What does this mean? A problem to solve

Can you read the above diagram ? A problem to solve