Sequence diagram 1 Models overview Soft Systems Model

Sequence diagram 1

Models overview Soft Systems Model Use case model Sequence diagram Activity diagram per use case Class diagram 2

How to model dynamic behavior of your application? • Use Case Diagram – high-level behaviors of the system, user goals, external entities: actors • Activity Diagram – flow of control between activities • Interaction diagrams - model how groups of object collaborate to perform some behavior (typically capture the behavior of a single use case) – Sequence Diagram – focus on time ordering of messages – Collaboration/Communication Diagram – focus on structural organization of objects and messages 3

Interaction diagrams • UML specifies a number of interaction diagrams to model dynamic aspects of the system • Typically used during analysis and design to document and understand the logical flow of your system • Interaction Diagrams - Set of objects or roles and the messages that can be passed among them. – Sequence Diagrams - emphasize time ordering – Communication Diagrams - emphasize structural ordering 4

What is sequence diagram? • Sequence diagram is an "interaction diagram" that models object interactions in a given scenario identified for a given Use Case. • What is scenario? – A scenario is a sequence of events that occurs during one particular execution of a system. 5

Key parts of a sequence diagram • • • Participant : an object or entity that acts in the sequence diagram Message: communication between participant objects The axes in a sequence diagram: – horizontal: which object/participant is acting – vertical: time (down -> forward in time) 6

Message Connections • The arrow indicates that: – The sender sends a message – The receiver receives the message – The receiver takes some action, returning the result to the sender The message must activate an operation in the receiving object 7

Sequence diagram notation: Lifelines : Object 1 : Object 2 Lifelines: Identify the existence of the object over time. 8

Sequence diagram notation: Sequence : Object 1 : Object 2 message Sequence: Vertical position signifies chronological sequence – earlier messages appear nearer the top. 9

Sequence diagram notation: Activations : Object 1 : Object 2 Activations: Indicate when an object is performing an action 10

Sequence diagram notation: Messages : Object 1 : Object 2 message Messages: Indicate the communications between objects 11

Types of messeges • Synchronous Messages - Sender waits for response to message before doing anything more. 12

An example of Synchronous Messages 13

Asynchronous Message • Used when the sender does not have to wait for a response – Typically an one way message – No response is sent 14

Message to self • Self-Call: A message that an object sends to itself. 15

Conditional interaction • Condition indicates when a message is sent – the message is sent only if the condition is true 16

“opt” Combined Fragment • The if-then Statement -> (opt) [condition] void apply. Brakes() { // the "if" clause: bicycle must be moving if (is. Moving){ // the "then" clause: decrease current speed current. Speed--; } } 17

“alt” Combined Fragment • The if-then-else Statement -> (alt) [condition] - separated by horizontal dashed line class If. Else. Demo { public static void main(String[] args) { int testscore = 76; char grade; if (testscore >= 91) { grade = 'A'; } else if (testscore >= 81) { grade = 'B'; } else if (testscore >= 71) { grade = 'C'; } else if (testscore >= 61) { grade = 'D'; } else { grade = 'F'; } System. out. println("Grade = " + grade); } } 18

Repeated interaction 19

“loop” Combined Fragment • While -> (loop) [condition or items to loop over] while (true) { // your code goes here } 20

Linking sequence diagrams • If one sequence diagram is too large or refers to another diagram, indicate it with either: – a "ref" frame that names the other diagram (Fig. 1) – an unfinished arrow and comment (Fig. 2) Fig. 1. “ref” frame Fig. 2. Another way of ref. 21

Task 1: Draw the following sequence diagram using RSA 22

Steps • • • File > New > Project Select UML Project (under Modeling) Give the name of the project: – Project name: Exercise_Sequence – Click Next • • Click on General, and then on Blank Package (selected by default) Give the name to the package: – File name: Exercise_Sequence – Click Finish • In the Project Explorer View, expand Exercise Sequence, and under Models, click on created package Exercise_Sequence – Right click on that package and click on Add Diagram, and select Sequence diagram. – Name the Sequence diagram as: sd. Exercise_Sequence • Using the elements from the Palette View, draw the desired diagram 23

Task 2: Create sequence diagram sd. User. Login § The user, as an actor, enters credentials into the Log. In form. § The Log. In form forwards user’s credentials to the application. § The application checks whether the user exists in the database. § If the user doesn’t exist in the database, the application notifies the user via the Log. In form. § If the password is incorrect, the application notifies the user via the Log. In form. § If everything is correct, the application welcomes the user with a message via the Log. In form. 24

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Task 2: Create sequence diagram sd. Voting § The Citizen (as an actor) chooses voting option on the webpage Voter. User. Form <<user interface, UI>> § Voter. User. Form forwards the received information to the application (<<controller>> Voting) § In the database, it is checked whether the user has already voted (<<Table>> Votes). § If the user has voted, then the application notifies the user that there is no possibility for re-voting. The application does so via the Voter. User. Form. § If the user has not voted: • The application retrieves the list of all the candidates from the database (<<Table>> Candidates) • The list of candidates is presented to the user via the Voter. User. Form. • The user selects a candidate and the application updates the information in the database accordingly *. 26

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