Computer Science CS425/CS6258/23/20011 The Architecting Phase Class diagrams are further refined in this phase of development Object diagrams are created Interaction diagrams are created Class skeletons are created to embody all analysis and design information created to this point in the development process

Computer Science CS425/CS6258/23/20012 Class Skeletons We will preview class skeletons to better understand the objectives of design Class skeletons are partial class definitions Class skeletons should be heavily commented, so that the purpose of all attributes, methods, and constructors is clear Class skeletons are the basis for the implementation phase of development

Computer Science CS425/CS6258/23/20013 Contents of Class Skeletons A list of the roles the class plays within the system Information concerning when objects of the class are created and deleted (information maintenance) For each role, the semantics of the class All attributes with access modifiers, types, names, and semantics For all constructors and methods, their signature, semantics, preconditions and postconditions

Computer Science CS425/CS6258/23/20014 LMS Class Skeleton

Computer Science CS425/CS6258/23/20015 System Decomposition Adds detail to the previous system representation Can be done iteratively or in a traditional, waterfall manner Each phase in the system development decomposes the system further Leads to a blueprint for implementation

Computer Science CS425/CS6258/23/20016 More UML Access Modifiers + means public - means private # means protected Constraints (restriction on the class) { } E.g {Students may check out at most 25 items} Tagged values also use { } E.g. {Requirement #5}

Computer Science CS425/CS6258/23/20017 More UML: Multiplicity Multiplicity or cardinality is represented above by the 0..1 and 0..* The above diagram indicates that a resource is checked out by 0 or 1 patrons and that each patron may check out 0 to many resources PatronResource 0..1 checks out 0..* Borrower

Computer Science CS425/CS6258/23/20018 More UML: Aggregation Patron Resource The solid diamond indicates that the Overdue form letter class consists of Patron and Resource objects. Solid diamond indicates that Patron and Resource classes exist in their own right Overdue form letter

Computer Science CS425/CS6258/23/20019 Aggregation Example from LMS where classes do not exist independent from aggregating class?

Computer Science CS425/CS6258/23/ Interaction Diagrams Interaction diagrams model dynamic aspects of the system by specifying the interaction among objects to produce a particular behavior Two types of interaction diagrams are defined in UML –Collaboration diagrams, which emphasize the structural organization of objects that send and receive messages –Sequence diagrams, which emphasize the time ordering of the messages passed between objects

Computer Science CS425/CS6258/23/ Notational Elements of Interaction Diagrams Object Link Message method(parameters) Object: class The object name is optional in the depiction of an object in UML notation An object is distinguished from a class in UML notation by the colon and underlining of the class name

Computer Science CS425/CS6258/23/ LMS: Collaboration Diagram : Patron : Library System : LibraryDatabase Checkout(ResourceID) validatePatron(MemDate) update(Patron) create(LibraryDatabase) getResource(ResourceID) getPatron(PatronID)

Computer Science CS425/CS6258/23/ Steps for Creating Collaboration Diagrams Identify a behavior to model Identify participating class and their relevant interrelationships Identify a specific scenario to model determine necessary message passing to carry out the behavior Introduce solution for object persistence, if needed

Computer Science CS425/CS6258/23/ Sequence Diagrams Like collaboration diagrams, sequence diagrams model dynamic aspects of the system by specifying the interaction among objects to produce a particular behavior Sequence diagrams specify the time ordering of messages Sequence diagrams show the life span of each object

Computer Science CS425/CS6258/23/ Check out resource Sequence Diagram : Patron : Library System : LibraryDatabase create(LibraryDatabase) getResource(ResourceID) getPatron(PatronID) validatePatron(MemDate)

Computer Science CS425/CS6258/23/ Evaluating Design Modeling software helps us produce correct, well- structured systems The resultant models can also be scrutinized for potential data integrity problems For example, in the LMS system, having update methods execute separately for the Patron and Resource objects may result in data integrity errors if system failure occurs between the initiation of the first method and the termination of the second method

Computer Science CS425/CS6258/23/ Object Diagrams Models a set of objects and their interrelationships during a system snapshot A system snapshot is the state of the software system at a selected moment of time Object diagrams model another static perspective of the system Unlike other diagrams, object diagrams may contain multiple instances of the same class

Computer Science CS425/CS6258/23/ LMS Case Study: Object Diagram (partial) currentP: Student: List name=“Gert Stein” libraryID= homephone= workphone= membership= expire= :Book name = “SOTY” author=“b. hooks” ISBN=... :Book name = “FOF” author=“Ehrenreich” ISBN=...

Computer Science CS425/CS6258/23/ Steps for Creating Object Diagrams Identify a system snapshot within a scenario to model Identify participating classes and their interrelationships Identify all allocated objects at the time of the snapshot Show the state of each object in the snapshot Determine all interobject links

Computer Science CS425/CS6258/23/ Code Reuse Collaboration diagrams are of particular use in pattern scavenging Pattern scavenging involves studying the various diagrams produced during analysis and class design to identify patterns of class interaction Once such patterns are found, they should be evaluated to determine if they can be effectively reused

Computer Science CS425/CS6258/23/ Reuse in LMS Resource Checkable Resource Reserve Resource BookElectronic Media

Computer Science CS425/CS6258/23/ Guidelines for Class Design Always keep data private Always initialize data in a constructor Do not use too many related primitives Not all attributes need individual accessor or mutator methods Order elements comprising class definitions consistently Break up overly complex classes into multiple classes Name classes, methods and attributes well

Computer Science CS425/CS6258/23/ Verification of the Class Design All system requirements developed during analysis must be addressed during design –All design documents must cross reference requirements from the requirements specification All required attributes and methods must be used properly –Eg data integrity of attributes must be enforced by update methods The modules comprising the system must work together properly

Computer Science CS425/CS6258/23/ Next Distributed systems –Corba, Java-RMI Design Documents – Reviews Implementation – Reviews Testing Integration Project Presentations