Transcript Object model

Requirements Model


Focus on WHAT, not HOW
Analyst needs to understand the problem
» How does software fit into overall systems?
» What are the customer’s concerns?
» How will the software solve the customer’s
problems


Serves as the contract between the customer
and the developer
Starting point for design
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Getting StartedUnderstanding the Customer
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Interview customer
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Understand the
current process
» Flow of information
» Form of information
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Decompose the
problem
Dillon: CSE470: Object Modeling
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Describe the
problem in the
customer’s
terminology
Have the customer
review, correct, and
refine the
description of the
problem
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Propose a Conceptual “Solution”
May model the current approach or
propose a completely new approach
 Present alternative approaches

» not alternative implementations, but
alternative conceptual approaches
Use UI prototype to help clarify issues
 Remember importance of maintainability
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» Plan for extensibility
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Purpose of Modeling
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Testing a physical entity before building
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Communication with customer
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Visualization
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Reduction of complexity
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Better understanding of the problem
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Early Modeling Notations
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Template-based natural languages
» SREM
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Boxes and arrows depicting data and
control flow
» SADT, IDEF
» Statecharts
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Data Structures
» Jackson Design Notation
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OO was the catalyst for new
OO modeling techniques
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Many different contenders
» Grady Booch, Rational Software
» Jim Rumbaugh, GE, OMT
» Ivar Jacobsen, Ericsson, use cases
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Unified Modeling Language (UML)
» Combines Booch, Rumbaugh, Jacobsen’s
techniques
» PL/1 of modeling languages
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Object Modeling Technique (OMT)
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Three complimentary views of the
system
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Object model (WHAT)
» Static, structural view of the system
» Describes objects in the system and their
relationships
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Object Modeling Technique (OMT)

Dynamic model (WHEN)
» Temporal, behavioral, control view of
system
» Interaction among objects
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Functional model (HOW)
» Transformational, function view of the system
» Describes the transformation of data
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Object Model
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Object - a concept, abstraction, or thing
» Promote understanding of problem domain
» Object is distinguishable and has identity
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Class - group of objects with
» similar properties,
» common behavior
» common relationships to other objects
» common semantics
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Object Model (cont.)
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An object is an instance of a class
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Attribute - a data value associated with
an object
» pure value, not an object
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Operation - a function or transformation
that may be applied to or by an object
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Object Model (cont.)
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Class Notation
Class Name
attribute
attribute: type = initial value
...
operation(arg-list): result-type
...
Attributes and operations shown depends on desired
level of detail
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Example: WEB Class
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Synchronous instructional web tool
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Use the Web Browser as sophisticated
data display
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Group-based communication model
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Reliable multi-cast communication
protocol
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WEB Class Components
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Browser synchronization
» Web_Instructor
– Detect changes in the instructor browser
– Format information into resources
– Send resources (reliably)
» Web_Student
– Receive and unpack resources
– Display resources through the web browser
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WEB Class Components
(cont.)
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Real audio stream
» Audio connection from the instructor to the
students
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Live connection
» Chat tool
» Feedback mechanism from the students to
the instructor
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Example Class Definitions
Web_Student
name: string
Web_Instructor
name: string
Helper_App
server_name: string
server_mime: string
server_path: string
Etc. ...
start_service
send_file(filename,URL)
spawn_viewer(appname,filename)
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Object Model: Associations
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Means for establishing relationships among
classes
» group of “links” with common structure and
semantics
– physical or conceptual connection between object
instances
» inherently bi-directional
» may be binary, ternary, or higher order
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Example: Association
Mreceiver
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Communicates with
Msender
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Object Model: Aggregation
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“Part-of” relationship
» associates an object representing an
assembly with the objects representing its
components
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Special form of association
» Transitive
» Antisymmetric
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Example: Aggregation
Web_Student
Browser_Wrapper
Browser_Slave
Mreceiver
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Object Model: Generalization
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“Is-a” relationship between classes
» Subclass(es) refine a superclass
» Superclass generalizes its subclass(es)
» Subclass(es) inherit attributes and
operations of the superclass
» Transitive association
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Example: Generalization
Web_User
name: string
Web_Student
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Web_Instructor
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Object Model: Multiplicities
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Indication how many instances of one
class may relate to an instance of
another class
Zero or more
One or more
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Exactly three
1+
One or more
2-6
From 2 to 6
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Example: Web Class Object
Model
Web_User
Web_Student
Web_Instructor
Browser_Slave
Mreceiver
Msender
Browser_Wrapper
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ViewerConfig
Helper_App
Browser_Listener
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Object Model: Creation Tips
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Understand the problem
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Keep it simple (initially)
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Choose good class
names
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Ignore multiplicities
Do not feel you have to
use all the constructs
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Concentrate on WHAT
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Document, document,
Look for binary
associations
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document!
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Refine until complete
and correct
(initially)
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