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Interaction Diagrams CSCI 4320 Interaction Diagrams Two Types of Interaction diagrams defined in UML • Collaboration Diagram – Emphasizes the structural organization of objects that send and receive messages via the method invocation • Sequence Diagram – Emphasizes the time ordering of those messages Collaboration Diagram • Shows the objects as well as the messages that are sent in a specific scenario • Objects are arranged to show message passing with a minimum of crossed lines • Example: Show a particular Patron object checking out a particular Resource object along with the methods that must be invoked to allow the checking out to occur. Patron Checking Out Resource ArgoUML 0.10.1 Sequence Diagram • Shows the lifeline of when an object is created and activation box of when the object is active. • Shows the flow of messages unambiguously • Vertical progression from the top of a sequence diagram to the bottom represents the progression of time. • Example: Shows the order in which methods must be invoked so that the Patron object can check out the Resource object Patron Checking Out Resource ArgoUML 0.10.1 Creating Your Sequence Diagram • ArgoUML – Collaboration and Sequence features are not active in latest version • Use the old version of ArgoUML 0.10.1 – This implementation is however not faithful to UML, nor to the look and feel of the rest of ArgoUML • Download Version 0.10.1 (ZIP file) http://argouml.tigris.org/servlets/ProjectDo cumentList?folderID=330 Evaluating Design • Reasons for modeling software before embarking on writing code – To produced well-structured, modular and correct code requires some planning. – Models allow us to evaluate the quality of the proposed solution without too large an investment of effort. – A sequence diagram that models a scenario may highlight some potential data inconsistencies Objectives of the Class Design Phase • Code Reuse • Well-designed Classes and methods • Assurance of data integrity Code Reuse • Do any classes intuitively form an inheritance hierarchy? – Software, Book, Resource – Savings, Checking, Account • Reuse instead of reinvent mechanisms for interaction – readString(length) used by readTitle() and readArtist() • Can classes share methods through a common abstract base class – Both GalleryPainting and AuctionedPainting use getTitle(), getArtist(), getSubject(), getHeight(), getWidth() – Create abstract base class Painting Well-Designed Classes and Methods • Always keep data private • Always initialize data in a constructor • Do not use too many related primitive types. – Create an aggregate class – Use Address class, rather than several attributes like street, city, zip • Not all attributes need individual accessor/mutator (get/set) methods • Name classes, methods and attributes to be self-documenting Data Integrity • Dirty Data: data that is inaccurate, outdated, or missing • Potential vulnerability stems from updating interrelated information in separate transactions or method invocations • Interrelated Information – Multiple data values that must be updated together in order to maintain data integrity – Example: When a Patron borrows a Resource both the Patron and the Resource object must be updated with similar information (DueDate) • Data integrity is at risk by malicious or inappropriate user access Things You Should Know • Compare and contrast collaboration and sequence diagrams • What are ways to support code reuse? • What are some rules to follow to create well-defined classes? • Describe a situation in which data Integrity can be compromised.
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