KF5008 Program Design & Development. Lecture 3 Sequence Diagrams

Transcription

1 KF5008 Program Design & Development Lecture 3 Sequence Diagrams

2 Learning Outcomes At the end of the lecture, you should be able to: Explain the content and purpose of a UML Sequence Diagram Describe the notation used in a UML Sequence Diagram Apply the notation to build UML Sequence Diagrams

3 Sequence diagrams Do not show links between objects Focus on the sequence of messages (ordering) Can show time constraints When used in analysis, parts of the notation may be omitted Important uses (in Design): Show design detail particularly UI Show actual UI classes, not analysis boundary classes

4 4 + 1 View of Architecture How are functional requirements dealt with? Software Module organisati Development View Logical View Scenario View Process View Key processes in the system and how they communicate Physical View Where will the softwar e run? What is it going to do? Any constraints?

5 Process View Behavioural aspects Communication Sequence diagrams Examine Behavioural aspects by behavioural modelling Includes non-functional attributes such as performance, availability Tasks A thread of control that can be uniquely executed Processes Groups of tasks which form an executable unit Addresses concurrency and distribution

6 Communication Diagrams Seen last year Show: objects and the links between them the messages that are passed. Order messages occur What is not shown Timing In previous versions of UML, communication diagrams were called collaboration diagrams.

7 A Complex Communication Diagram sd Book Room 4: book() 3: checkavailability() :Administrator :BookRoomUI 4.1: book() 3.1: checkavailability() 2: startinterface() 4.1.1: addnewbooking() *[for all bookings] : getbooking() :Booking :BookRoom :Room 1*[for all rooms]: getroom() 3.1.1: isfreeat() : addbooking() newbooking :Booking

8 Sequence Diagrams Illustrate the objects that participate in a use-case use-case scenario complicated method Show the messages that pass between objects The order this occurs What is not shown in detail Timing

9 Why send messages? To tell another object to do something. Create an instance, delete yourself, work something out, do something you are responsible for. To give another object information. Add information, change information. To ask another object for information. Get information.

10 Sequence Diagram Making Instant Coffee : Person findkettle( ) : Kettle CheckWater( ) water required [water required]addwater( ) switchon( ) [until boiled]heatup( ) fetchcup( ) mycup : Cup boiled addinstantcoffee( ) fillcup(mycup : Cup) fillwithwater( )

11 Sequence Diagram Syntax AN ACTOR AN OBJECT anobject:aclass A LIFELINE A FOCUS OF CONTROL A MESSAGE OBJECT DESTRUCTION amessage() x

12 Exercise Attempt to draw a simple sequence diagram for getting out of bed in the morning / afternoon. Use the objects Person Alarm clock Assume the events that occur are: Alarm Clock rings Person switches off alarm clock Person gets out of bed This should take no more than 3-5 minutes

13 Getting up : Person : AlarmClock alarm sounds switchoffalarm( ) get up

14 A more complex sequence diagram What is missing? : LoginControl : Student login(username : String, password : String) : LoginUI 1. Datastore access startinterface( ) login(username : String, password : String) Students( ) : Students students login(username : String, password : String) [not student]informbaduser NamePassword( ) [student] hide( ) student showmenu(student : Student) : MenuControl startinterface(student : Student) : MenuUI

15 Message types Synchronous (call) message Reply Asynchronous message Creation message Message Types for Sequence Diagrams

16 Building a Sequence Diagram Determine the context of the sequence diagram Identify the participating objects Set the lifeline for each object Add messages Place the focus of control on each object s lifeline Determine object destruction Validate the sequence diagram Check consistency with other models and refactor

17 Example

18 Example sd Calculate Balance Owing :Order Clerk :Customer :Order Interaction Constraint getbyname :Invoice Call Messages getbalanceowing Object lifeline loop [For all customer s orders] Interaction Operator getorder getbalance Combined Fragment (loop) loop Activation or Execution [For all order s invoices] getinvoice calculatebalance

19 Replies and activation sd Calculate Balance Owing :Order Clerk :Customer :Order getbyname getbalanceowing Synchronous Message getorder Send Message Event Occurrence Receive message Event occurrence start of Execution Occurrence Execution Occurrence end of Execution Occurrence Message reply showing return of control

20 Replies sd Calculate Balance Owing : Order Clerk :Customer :Order :Invoice getbyname name = getbyname getbalanceowing loop [For all customer s orders] getorder getbalance loop [For all order s invoices] getinvoice calculatebalance balance = calculatebalance Reply returns control, and sometimes a return value, to the calling object. Replies may be shown explicitly - note dashed line and optional return value.

21 Focus of control (not normally supported by tools) sd Calculate Balance Owing : Order Clerk : Customer : Order : Invoice getbyname name = getbyname getbalanceowing loop [For all customer s orders] getorder getbalance loop Focus of Control: times during an activation when processing takes place within that object. [For all order s invoices] getinvoice calculatebalance balance = calculatebalance

22 Creating objects Notice Noticethe theline linegoes goes into intothe thebox box not notto to the theline linebelow belowit. it.

23 Destroying objects sd Receive payment :Customer :Order Clerk :Order :Invoice getbyname paymentreceived getorder settleinvoice The Thedashed dashedline linedoes does NOT NOTcontinue continuedown downthe the page delete

24 Branching sd Add new order :Order Clerk Branching may be derived from an extension relationship between two use cases on the use case diagram, or from exceptions :Customer getbyname neworder alt [balanceowing<limit] Order neworder:order [else] Branching: alternative pathways through a Use Case CM0502 Lecture 8 WarningMessage 24 newmess:warningmessage

25 Iteration sd Calculate Balance Owing CM0502 Lecture 8 25

26 Common interaction operators loop Used for loops. opt optional Used for messages which are either executed or not alt alternative Used where there is an if/else situation Can be >= 2 alternatives

27 Activity 1: ATM Create Sequence Diagram for Use Case UC:ATM Withdraw Cash 1. This use case starts when the user selects the Withdrawal option. 2. The ATM asks for the amount. 3. The user enters the amount and presses Enter. 4. The ATM verifies that the amount is within the predefined limits and asks the banking network to process the transaction. 5. The banking network checks with the bank to find out if the funds are available. 6. The bank verifies that the amount is available, and updates the account. 7. The bank returns authorisation for the withdrawal and the new account balance. 8. This use case ends when the ATM dispenses the cash.

28 Solution Note: no Object creation/ destruction : BankingNetwork : ATM : User : Account : Bank withdrawal( ) amount enteramount(am ount : Double) withinlimits(amount : Double, account : Account) processtransaction(amount : Double, account : Account) fundsavailable(amount : Double) fundsavailable(amount : Double, account : Account) available updateaccount(amount : Double, account : Account) updated completed completed cash

29 Additional Exercise We all know things that can go wrong in withdrawing money from an ATM. Enhance the use case description by adding these. Using the alt, opt and loop operators as necessary, construct a sequence diagram which caters for the additional aspects.

30 Managing Sequence Diagrams Our examples have been fairly simple, but some sequence diagrams become very complex. Part of the logic may used in more than one place Perhaps it represents an «include». In these cases, it can be useful to hide the details of parts of the interaction. They can then be shown in full on a separate diagram. CM0502 Lecture 9 30

31 Example sd Process Payment :Order Clerk :Customer :Order :Invoice getbyname getbalanceowing ref Calculate Balance Owing Gate showing message entering the interaction occurrence receivepayment Remainder of diagram omitted. RSA calls this an interaction use

32 Example (2) sd Calculate Balance Owing :Customer :Order :Invoice getbalanceowing loop Gate showing message entering the interaction fragment [For all customer s orders] getorder getbalance loop [For all order s invoices] getinvoice calculatebalance

33 Boundary and Control Objects You might have wondered why the examples do not include boundary and control objects. These can be used on sequence diagrams if required, especially if used at the analysis stage, in which case they are used in the same way as in communication diagrams. However, not all analysts or all development methods use them. In design, sequence diagrams can show the actual interface objects (windows, buttons ) rather than a single boundary object. CM0502 Lecture 9 33

34 Example (3)

35 Implementing Sequence Diagrams Establish interaction context - system, subsystem, operation, scenario. Identify the objects that take part in the interaction. Lay out the objects with the most important objects on the left (usually actors are at the very lefthand of the diagram). Establish lifelines for each object. Indicate construction and destruction. Add messages at appropriate points in the object lifelines. Show activation. Focus of control is more difficult and not supported by all CASE tools. Activation is automatic in many tools, including StarUML.

36 Model Consistency The allocation of operations to objects must be consistent with the class diagram and the message signature must match that of the operation Can be enforced through CASE tools Every sending object must have the object reference for the destination object Either an association exists between the classes or another object passes the reference to the sender

37 Summary In these lectures you have learned about: How to develop object communication from use cases How to model object communication using an sequence diagram How to model object communication using an communication diagram How to cross-check between interaction diagrams and a class diagram

38 Further Reading UMLSequenceDiagrams.pdf