Transcript SYST37028 - Sheridan College

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Today
o Sequence Diagrams- View & Data Layers
• Message syntax
o Design Class Diagrams
o Cohesion & Coupling
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One-to-many with superior to
subordinate. The visibility goes
from the superior to the
subordinate
Mandatory relationships for
existence. Visibility goes from
independent to dependent
Object needs information from
another object. Visibility goes to
object with the information
Navigational arrows may be
bidirectional
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UML does not distinguish between design class notation and
domain model notation
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Domain model class diagram shows conceptual classes in
users’ work environment
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Design class diagram specifically defines software classes
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UML uses stereotype notation to categorize a model element
by its characteristics
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Navigation visibility
o Describes which objects can interact with each other
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Coupling
o Measures how closely classes are linked
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Cohesion
o Measures the consistency of functions in a class
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Separation of responsibilities
o Divides a class into several highly cohesive classes
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Coupling – qualitative measure of how closely classes in a
design class diagram are linked
o Number of navigation arrows in design class diagram or
messages in a sequence diagram
o Loosely coupled – system is easier to understand and maintain
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Cohesion – qualitative measure of consistency of functions
within a single class
o Separation of responsibility – divide low cohesive class into
several highly cohesive classes
o Highly cohesive – system is easier to understand and maintain
and reuse is more likely
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Reference & Example:
o http://en.wikipedia.org/wiki/Coupling_(computer_programming)
o http://www.scribd.com/doc/60141117/6/Tightly-Coupled-vs-
Loosely-Coupled-Systems
o http://soa.sys-con.com/node/439723
o http://stackoverflow.com/questions/2868627/why-should-a-webarchitecture-be-loosely-coupled
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A multi layered system
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Example – Create new Customer for a Customer
Relationship Management System (CRM)
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