Computer Science CS425/CS6258/23/20011 The Architecting Phase Class diagrams are further refined in this phase of development Object diagrams are created

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


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


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


LMS Class Skeleton


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


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}


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


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


Aggregation

• Example from LMS where classes do not exist independent from aggregating class?


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


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


LMS: Collaboration Diagram

: Patron

: Library System

: LibraryDatabase

Checkout(R

esource

ID)

validate

Patron(M

emDate

)

update(Patron)

create(LibraryDatabase)

getResource(ResourceID)

getPatron(PatronID)


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


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


Check out resource Sequence Diagram

: Patron : Library System : LibraryDatabase

create(LibraryDatabase)

getResource(ResourceID)

getPatron(PatronID)

validatePatron(MemDate)


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


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


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= ...


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


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


Reuse in LMS

Resource

CheckableResource

ReserveResource

Book Electronic

Media


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


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


Next

• Distributed systems– Corba, Java-RMI

• Design Documents – Reviews• Implementation – Reviews• Testing• Integration• Project Presentations