1University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 1Lecture 2:Introduction to Modeling Why Build Models? What types of Models to build Intro to UML Class Diagrams Reverse Engineering…University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 2Getting started You’ve just joined an ongoing project Where do you start? (oh, BTW, the project doesn’t really have any documentation) Reverse Engineering: Recover design information from the code Create higher level views to improve understanding E.g. Structure of the code Code Dependencies Components and couplings E.g. Behaviour of the code Execution traces State machines models of complex objects E.g. Function of the code What functions does it provide to the user?2University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 3Why build models? Modelling can guide your exploration: It can help you figure out what questions to ask It can help to reveal key design decisions Modelling can help to uncover problems Inconsistency in the models can reveal interesting things… e.g. conflicting or infeasible requirements e.g. confusion over terminology, scope, etc e.g. disagreements between stakeholders Modelling can help us check our understanding Reason over the model to understand its consequences Does it have the properties we expect? Animate the model to help us visualize/validate the requirements Modelling can help us communicate Provides useful abstracts that focus on the point you want to make …without overwhelming people with detailUniversity of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 4Dealing with problem complexity Abstraction Ignore detail to see the big picture Treat objects as the same by ignoring certain differences (beware: every abstraction involves choice over what is important) Decomposition Partition a problem into independent pieces, to study separately (beware: the parts are rarely independent really) Projection Separate different concerns (views) and describe them separately Different from decomposition as it does not partition the problem space (beware: different views will be inconsistent most of the time) Modularization Choose structures that are stable over time, to localize change (beware: any structure will make some changes easier and others harder)3University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 5the Unified Modelling Language (UML) Third generation OO method Booch, Rumbaugh & Jacobson are principal authors Still evolving (currently version 2.0) Attempt to standardize the proliferation of OO variants Is purely a notation No modelling method associated with it! Was intended as a design notation Has become an industry standard But is primarily promoted by IBM/Rational (who sell lots of UML tools, services) Has a standardized meta-model Use case diagrams Class diagrams Message sequence charts Activity diagrams State Diagrams Module Diagrams Platform diagrams …University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 6UML viewsClass Diagramsinformation structure;relationships betweendata items;modular structure forthe system;Statechartsresponses to events;dynamic behavior;event ordering,reachability,deadlock, etc.Activity diagramsbusiness processes;concurrency andsynchronization;dependenciesbetween tasks;Sequence Diagramsindividual scenario;interactions betweenusers and system;Sequencing ofmessages;Use Casesuser’s view;Lists functions;visual overview of themain requirements;4University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 7Intro: Object Classes in UML:patientNameDate of Birthphysicianhistory:in-patientRoomBedTreatmentsfood prefs:out-patientLast visitnext visitprescriptions:patientNameDate of Birthphysicianhistory:heartNatural/artif.Orig/implantnormal bpm:eyesNatural/artif.Visioncolour:kidneyNatural/artif.Orig/implantnumberSource: Adapted from Davis, 1990, p67-6810..10..21..20..1 0..1Generalization (an abstraction hierarchy)Aggregation(a partitioning hierarchy)University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 8:patientNameDate of BirthHeightWeight:In-patientRoomBedPhysician:Out-patientLast visitnext visitphysician:heartNormal bpmBlood type:eyeColourDiameterCorrection:kidneyOperational?generalizationaggregationClass nameattributesservices0..111..20..10..20..1multiplicities:organNatural/artif.Orig/implantdonor5University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 9What are classes? A class describes a group of objects with similar properties (attributes), common behaviour (operations), common relationships to other objects, and common meaning (“semantics”). Examples employee: has a name, employee# and department; an employee is hired, and fired; anemployee works in one or more projects:employeenameemployee#departmenthire()fire()assignproject()Name (mandatory)Attributes (optional)Operations (optional)University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 10Fred_Bloggs:Employeename: Fred BloggsEmployee #: 234609234Department: MarketingObjects vs. Classes
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