22/09/2012 INFO2110. Copyright Warning. Revision of class diagram. Overview. Purpose of class diagram. Generalization Relationship

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1 22/09/202 INFO20 Copyright Warning System Analysis and Modelling Semester 2, 202 Lecture 8, Structural Modelling (II) COMMONWEALTH OF AUSTRALIA Copyright Regulations 969 WARNING This material has been reproduced and communicated to you by or on behalf of the University of Sydney pursuant to Part VB of the Copyright Act 968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Slides Prepared by Vera Chung; Including slides courtesy of Ying Zhou, B. Selica; material provided for Dennis, Wixcom, & Tegarden System Analysis and Design with UML 2009 John Wiley & Sons, Inc. All rights reserved; slides from other reference books Do not remove this notice. 2 Overview Revision of class diagram Modelling Examples - Revision - class diagram - Generalization - Attributes and operations - CRC cards From text to diagrams - General modelling skills - Example : general description - Example 2: use case text - Example 3: general description - Example 4: In class example Overview: The class diagram is a static diagram. It represents the static view of an application. Class diagram is not only used for visualizing, describing and documenting different aspects of a system. But also for construction executable code. The class diagram describes the attributes and operations of a class. And the constraints imposed on the system. It shows a collection of classes, interfaces, associations, collaborations and constraints. It is also known as a structural diagram. 3 4 Purpose of class diagram Generalization Relationship Analysis and design of the static view of an application. Describe the responsibilities of a system. Base for component and deployment diagrams. Forward and reverse engineering. The generalization abstraction enables the analyst to create clases that inherit attributes and operations of other classes Subclass: needs to have at least something different from the super class or other subclasses Superclass: hold common attributes and operations such as employee id, salary etc Generalization notation Secretary Engineer reportsto..*. assignedto..3 Project 6

22/09/202 Semantics of UML Generalization Generalization example Subclasses = specialized subsets of parent Subclass inherits all features of the parent and may add its own Shape position : Point Set

2 22/09/202 Semantics of UML Generalization Generalization example Subclasses = specialized subsets of parent Subclass inherits all features of the parent and may add its own Shape position : Point Set of all instances of Shape s3 s sp s sn Person Patient Q: How do you handle the case when a doctor is also a patient? A: We just create a new record for that, we do not want to mess the employee record with the patient record. We do not need to know that the patient is also an employee. This is different from the Child case. Ellipse Polygon Spline sides : Integer Nurse Doctor courtesy of B. Selica 7 8 Useful Generalization Relationship There are many possible generalizations, be selective! Choose the one that is useful to the system you are analysing! Customer Correct? Yes But useful? Depends! They are the responsibilities of the class A manager knows her special address (knowing) A manager assigns tasks to other employees (doing) Attributes and Operations assigntask() In analysis stage, the identified operations can be in various levels: some large ones that require collaboration with other objects; others may just have a few steps. It is often beneficial to identify high level behaviours MaleCustomer FemaleCustomer The operations identified in analysis stage may not have a one to one mapping to methods of classes; The main goal of such practice is to help understand the class concept in terms of responsibilities as well as behavioural features 9 0 CRC Card Front-Side of a CRC Card Stands for Class-Responsibility-Collaboration - The second C can be referred to as Collaborator - Other classes that this class needs to work with Is created per Class Emphasis individual class responsibilities and collaborations - In contrast, Class Diagram emphasis the overall structure, association is more important than showing individual attributes and operations - Such angle is important as it gets you away from the notation of classes as dumb data holders and helps the project team to understand the high level behaviour of important classes How do we find all elements in a CRC card - By executing use cases in terms of objects (classes) 2 2

22/09/202 Back-Side of a CRC Card General Modelling Skills Object identification - Reuse or modify existing models - There are published, well-crafted domain models and data models for common

. - Books: Analysis patterns by Martin Fowler, Data Model Patterns by David Hay, Data Model Resource Book by Len Silverston - Use a category list - Physical or tangible objects like Register,

3 22/09/202 Back-Side of a CRC Card General Modelling Skills Object identification - Reuse or modify existing models - There are published, well-crafted domain models and data models for common domains: inventory, finance, health.. - Books: Analysis patterns by Martin Fowler, Data Model Patterns by David Hay, Data Model Resource Book by Len Silverston - Use a category list - Physical or tangible objects like Register, Airplane - Places like Store, Airport - Transactions like Sales, Order, Reservation - etc. - Textual analysis - Noun or noun phrases are good candidates of classes/instances - Various verbs may suggests associations or operations - etc. (Figure 6-) in textbook has a long list of possible mappings 3 4 Creating CRC cards and Class Diagram General Modelling Skills (II) - No agreed upon order on which one should be created first - Class Diagram as domain model is always created during the analysis stage - CRC cards can be created during the design stage or when we are analysing the behavioural aspects of the system - CRC cards are tightly associated with use case text and sequence diagram - Class Diagram can be created based on all sorts of textual description Creating Class Diagram - Object identification - Adding associations - Adding attributes and operations A system to display photos Example : general description Michael Smith is a fanatical photographer he often takes new photos with his digital camera, and tries to select them on his computer screen. When his camera is connected to his computer, photos will sequentially arrive from the left side of the screen and push all existing ones on the screen to the right. Assume that there is only one row of photos being displayed and the height of each photo is less or equal to the height of the screen. If a photo is pushed to the right side and part of it is outside the screen, the whole photo will disappear. When watching the photos, Michael may also pick up his disfavored photos to make more space for new photos. He can pickup any photo on the screen. Your task is to write a simulator that will keep track of photos remaining on the screen. Photos in each simulation will be identified by a unique name and its width. 5 6 Textual analysis identifying objects Not exactly an attribute, but suggests Actor, outside system boundary certain attributes of screen and photo Michael Smith is a fanatical photographer he often takes new photos with his digital camera, and tries to select them on his computer screen. When his camera is connected to his computer, photos will sequentially arrive from the left side of the screen and push all existing ones on the screen to the right. Assume that there is only one row of photos being displayed and the height of each photo is less or equal to the height of the screen. If a photo is pushed to the right side and part of it is outside the screen, the whole photo will disappear. When watching the photos, Michael may also pick up his disfavored photos to make more space for new photos. He can pickup any photo on the screen. Your task is to write a simulator that will keep track of photos remaining on the screen. Photos in each simulation will be identified by a unique name and its width. Similar as SUD System under development Photo name width location pushright displays on 0.. Screen width photoarrive pickupphoto Create Class Diagrams Note: structural model is different from ERD diagram. In this example, both classes do not require persistence Suggest screen has certain size 7 8 3

4 22/09/202 Example 2: use case text Textual analysis An use case example from week 6 lecture SUD: Management System An actor, but also an import concept in the system A term baffles many students Similar as, both an actor and a concept in the system Use-case: employee takes leave Normal flow: -. gives system information about the leave request - 2. System sends request to manager for approval -. gives system information about the leave request - 3 sends approved request to system - 2. System sends request to manager for approval - 4. System sends leave information to external payroll system - 3 sends approved request to system - 4. System sends leave information to external payroll system - 5. System send leave information to calendar tool - 6. System sends employee message about approved leave an actor - 5. System send leave information to calendar tool - 6. System sends employee message about approved leave 9 May suggest an attributed of the Request (e.g. status) A separate concept or just some information from the leave request class? Similar as leave information, may be a new class or just something from leave request class Either an actor or a component consists of many concepts or just a concept 20 Creating Class Diagram The tricky system concept/term It appears a lot in all sorts of textual descriptions: interviews, use case text apply leave Applies for LeaveRequest status recorded on 0.. CalendarTool It plays an important interface and control role Its meaning is a bit vague, sometimes deliberately so How do we handle it? Q: Is Calendar tool an external system? A: No it is part of the system Q: Is it a subsystem, component which contains many objects? A: We are not sure at this stage, just model it as a whole approves approve leave Q: Can an employee apply for many leaves at the same time? A: yes Totally ignore it Use proper boundary or control class to represent it How do we determine which option to follow Depends on what you want to do in analysis stage 2 22 If you want to do some behavioural modelling in analysis stage Analysis & Design - You need to find some boundary or control classes and put it in the class diagram If you do behavioural modelling in design stage - You may ignore the system in class diagram More analysis oriented Behavioural Modelling -what -requirements -investigation of domain -understanding of problem More design oriented -how -logical solution -understanding and description of solution Essential style in both use case and class diagram Always try to avoid mentioning/hinting any solution in analysis stage Compare these two writings Patient identifies self (from lecture notes) Against The patient provides the receptionist with his or her name and address The receptionist validates that the patient exists in the patient database (from textbook) The first one follows recommended style for written use cases The second one does suggest solution and mention some software component such as database A even worse one would be The patient provides the receptionist with his or her name and address in a dialog box Same rule for class diagram

5 22/09/202 Boundary, control and entity class Updated version Boundary class - A class that represents the interface between the actor and the system Control class - A class that controls the flow of a use case Entity class - A class that represents the persistent information tracked by the system Most of the classes we identified so far are entity classes - Control classes are often created per use case (not part of the problem domain at all) - ApplyLeaveControl - Boundary classes may be discovered from a use case text - The employee fill out a form to send a leave request apply leave ApplyLeaveControl The control class can stand by its own or even omitted Applies for LeaveRequest status approves approve leave recorded on 0.. CalendarTool The concepts are taken from I. Jacobson. G.Booch, & J. Rumbaugh, The Unified Software Development Process, Example 4: In-class case study DownTown Video is a chain of video stores scattered through out a major metropolitan area. The owner of the chain is considered to have a new movie rental system for it. Customers information are processed by the system. DownTown Video considers each family to be a customer, so special promotions are offered to each household. For any given customer, several people may be authorized to rent movies. The primary contact for each customer can also establish rental parameters for other members of the household. For example, if a parent wants to limit a child s rental authorization to only PG and PG-3 movies, the system will be able to handle that. How to draw Class Diagram: Summary - The name of the class diagram should be meaningful to describe the aspect of the system. - Each element (nouns) and their relationships (verbs) should be identified in advance. - Responsibility (attributes and methods) of each class should be clearly identified. - For each class, minimum number of properties should be specified. - The diagram should be drawn on plain paper and rework as many times as possible to make it correct as final version. 27 Summary Where to use Class Diagrams? - Describing the static view of the system. - Showing the collaboration among the elements of the static view. - Describing the functionalities performed by the system. - Construction of software applications using object oriented languages. 5

Object-Oriented Software Engineering Practical Software Development using UML and Java

Object-Oriented Software Engineering Practical Software Development using UML and Java Chapter 5: Modelling with Classes Lecture 5 5.1 What is UML? The Unified Modelling Language is a standard graphical