Modeling Behaviour. Objectives

Transkript

1 Modeling Behaviour Modeling Behaviour 1 Objectives To explain why we model behaviour? To Introduce Statechart Diagrams. To Explain the relationship to Class Diagram, Sequence Diagram, Collaboration Diagram. Modeling Behaviour 2

2 Why Model Behaviour? A Class Diagram is a static view of object classes and their associations. A Behaviour Model is used to understand system aspects such as: change, response to external stimuli, time. Modeling Behaviour 3 Why Model Behaviour? Behaviour is that aspect of the system that describes the sequences of operations that occur in response to external stimuli. This has particular importance where sequence of processing is an issue - e.g. interactive, real-time and control systems. Modeling Behaviour 4

3 Statecharts These are state transition diagrams (with some additions) which describe the lifetime of some object (a person, a student, ) Transitions are supposed to represent actions which occur quickly and are not interruptible. States are supposed to represent longerrunning activities. What constitutes quickly and longer-running depends on the application. Modeling Behaviour 5 State Diagram for Purchase Order /get order Checking Do/check items [all items in stock] Dispatching Do/package items start Item received [some item not In stock] Waiting [some item not In stock] Item received [all items in stock] /deliver package Delivered Modeling Behaviour 6

4 Statecharts Key concepts: Events & States An event happens in the world and the system needs to know about it. Following an event, objects within the system may receive a message to act (each action is an operation). Following each message an object normally remains in the same state until another message arrives. Modeling Behaviour 7 Course Lifetimes Initialization offernewcourse/set count=0 ^create(courseroster) addstudent[count<10] Open [count=10] Closed cancel cancel quarterstarted [Lochovsky98] Canceled /delete(courseroster) Modeling Behaviour 8

5 UML events Change events designate when a condition becomes true E.g., when(balance < 0) Signal events designate the receipt of an explicit (real-time) signal from one object to another Call events indicate the receipt of a call for an operation by an object Time events mark the passage of a designated period of time E.g., after(10 seconds) Modeling Behaviour 9 States A state represents a time period during the life of an object during which the object satisfies some condition, performs some action or waits for an event. In general a state can be characterized by a predicate which is true while the state is on. Such a predicate may be defined in terms of: The value(s) of one or more attributes of the class E.g., a person s address The existence of a link to another object Modeling Behaviour 10

6 Statechart Diagrams A statechart diagram is prepared for every class with non-trivial behaviour. Statechart diagram shows: All events affecting that class; All its possible states. Used to: Cross-check against Sequence Diagrams; Identify operation triggers/parameters /constraints. Modeling Behaviour 11 Statechart Diagrams - Notation Generalised notation Start State 1 event(parameters)[condition]/action State 2 End Modeling Behaviour 12

7 Statechart Diagrams - Transitions Actions are processes that occur quickly and are not interruptable Conditions (a.k.a. Guard) return a logical True/False - the transition occurs on True When there is no Event in the label the transition occurs as soon as the activities of the current state are completed A Send-clause is a special case of an action: dest-expression.dest-message name(argument) Modeling Behaviour 13 Internal actions and activities for a state Some states represent the lifetime of an activity that takes time to complete starts when a state is entered either completes or is interrupted by an event that causes an outgoing transition Special activity constructs: do/statediagramname(parameterlist) -- calls another state diagram entry/action -- carry out the action when entering the activity exit/action -- carry out the action when exiting Modeling Behaviour 14

8 Internal actions and activities for a state State 1 entry: action do: activity exit: action Modeling Behaviour 15 Course Lifetimes, Again Initialization do / Initialize addstudent [count<10] addstudent/ count=0 ^Course.Create() Open entry / RegisterStudent exit / Course.AddStudent(student) cancel [count=10] Cancelled Course.Delete() cancel Closed do / FinalizeCourse quarterstarted Modeling Behaviour 16

9 Nested (Super) States State transition diagrams can be very hard to read once they grow to more than a few dozen states. For UML statecharts diagrams, states can be composed into nested states. Such compositions make it possible to view a state at different levels of abstraction. Modeling Behaviour 17 Nested (Super) States Transmission select N Neutral select F select R select N Reverse Forward Modeling Behaviour 18

10 Nested (Super) States Transmission Neutral select R select N Reverse select N select F Forward stop First upshift downshift Second upshift downshift Third Modeling Behaviour 19 Class Diagram: Order Processing line items * Order datereceived isprepaid number:string price:money check item close() dispatch() initiate delivery item 1 OrderLine issatisfied:boolean price:money quantity:integer * CorporateCustomer contactname creditlimit creditrating billformonth(integer) remind() * * 1 Product 0..1 Customer address name 1 creditrating():sring PersonalCustomer creditcard# Employee {creditrating() =="poor"} Modeling Behaviour 20

11 Supertransition Where transitions may occur from several states to a single state the Statechart Diagram may show this single state as a Supertransition e.g. a Purchase Order may be cancelled at any point prior to delivery. This may be drawn with several transitions or by creating a Superstate. Modeling Behaviour 21 Order Statechart Diagram Order Start get next item [Not all items checked] Checking do: check item /get first item [All items checked && all items available] Dispatching do: initiate delivery [All items checked && some items not in stock] Waiting Item Received [all items available] Delivered Item Received [some items not in stock] Delivered Add a new state and separate transitions to the diagram to show that an order can be cancelled at any point before it is delivered. Modeling Behaviour 22

12 Order Statechart Diagram: Superstates & Supertransition Order Start Superstate name get next item [Not all items checked] /get first item Checking do: check item [All items checked && all items available] Active Dispatching do: initiate delivery [All items checked && some items not in stock] Waiting Item Received [all items available] Item Received [some items not in stock] cancellation Cancelled Delivered Modeling Behaviour 23 Concurrent States Used when a given object has sets of independent behaviours e.g. A purchase order may be in the state of being checked but also in a separate state of being authorised When the superstate is on, all of their component states are on Modeling Behaviour 24

13 Concurrent States:Order Waiting Cancelled Checking Dispatching Delivered Authorizing Authorized Rejected Modeling Behaviour 25 Complex Statechart Transitions Transition to superstate boundary transition to initial state of the superstate. entry actions of all regions entered are performed There may also be transitions directly into a complex state region (like program gotos ). Transition from a superstate boundary transition from the final state of the superstate exit actions of all regions exited are performed Modeling Behaviour 26

14 Complex Statechart Transitions There may be transitions directly from within a complex state region to an outside state A complex transition may have multiple source and target states. Modeling Behaviour 27 Statecharts & Relationship to Other Diagrams Events on the statechart diagram should appear as an incoming message for the appropriate object on a sequence and collaboration diagram. A statechart diagram is prepared for every object class in the Class Diagram with nontrivial behaviour. Every event should correspond to an operation on the appropriate class. Modeling Behaviour 28

15 Statecharts & Relationship to Other Diagrams Every action should correspond to the execution of an operation on the appropriate class. Entry/Action, Exit/Action and Do/Activity within a State will normally be equivalent to Operations in the Class Diagram. Every outgoing message sent from a statechart must corrrespond to an operation on another class. Modeling Behaviour 29 Additional Readings [Booch99] Booch, G. et all. The Unified Modeling Language User Guide. Chapters 19, 20, 21, 24. Addison-Wesley. [Fowler00] Fowler, M. et all. UML Distilled: A Brief Guide to the Standard Object Modelling Language. Chapters 8, 9. Addison-Wesley. Modeling Behaviour 30