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CS425/CS625 8/23/2001 1Computer Science
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
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CS425/CS625 8/23/2001 2Computer Science
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
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CS425/CS625 8/23/2001 3Computer Science
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
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CS425/CS625 8/23/2001 4Computer Science
LMS Class Skeleton
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CS425/CS625 8/23/2001 5Computer Science
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
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CS425/CS625 8/23/2001 6Computer Science
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}
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CS425/CS625 8/23/2001 7Computer Science
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
Patron Resource0..1 checks out 0..*
Borrower
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CS425/CS625 8/23/2001 8Computer Science
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
Overdueform letter
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CS425/CS625 8/23/2001 9Computer Science
Aggregation
• Example from LMS where classes do not exist independent from aggregating class?
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CS425/CS625 8/23/2001 10Computer Science
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
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CS425/CS625 8/23/2001 11Computer Science
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
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CS425/CS625 8/23/2001 12Computer Science
LMS: Collaboration Diagram
: Patron
: Library System
: LibraryDatabase
Checkout(R
esource
ID)
validate
Patron(M
emDate
)
update(Patron)
create(LibraryDatabase)
getResource(ResourceID)
getPatron(PatronID)
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CS425/CS625 8/23/2001 13Computer Science
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
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CS425/CS625 8/23/2001 14Computer Science
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
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CS425/CS625 8/23/2001 15Computer Science
Check out resource Sequence Diagram
: Patron : Library System : LibraryDatabase
create(LibraryDatabase)
getResource(ResourceID)
getPatron(PatronID)
validatePatron(MemDate)
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CS425/CS625 8/23/2001 16Computer Science
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
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CS425/CS625 8/23/2001 17Computer Science
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
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CS425/CS625 8/23/2001 18Computer Science
LMS Case Study: Object Diagram
(partial)
currentP: Student : Listname=“Gert Stein”libraryID=6747632homephone=5554321workphone=5551234membership=05011999expire=05012002
:Bookname = “SOTY”author=“b. hooks”ISBN= ...
:Bookname = “FOF”author=“Ehrenreich”ISBN= ...
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CS425/CS625 8/23/2001 19Computer Science
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
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CS425/CS625 8/23/2001 20Computer Science
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
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CS425/CS625 8/23/2001 21Computer Science
Reuse in LMS
Resource
CheckableResource
ReserveResource
Book Electronic
Media
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CS425/CS625 8/23/2001 22Computer Science
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
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CS425/CS625 8/23/2001 23Computer Science
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
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CS425/CS625 8/23/2001 24Computer Science
Next
• Distributed systems– Corba, Java-RMI
• Design Documents – Reviews• Implementation – Reviews• Testing• Integration• Project Presentations