Requirements Model

1
Requirements Model

• Focus on WHAT, not HOW
• Analyst needs to understand the problem
• How does software fit into overall systems?
• What are the customers concerns?
• How will the software solve the customers
  problems
• Serves as the contract between the customer and
  the developer
• Starting point for design

2
Getting Started-Understanding the Customer

• Interview customer
• Understand the current process
• Flow of information
• Form of information
• Decompose the problem

• Describe the problem in the customers
  terminology
• Have the customer review, correct, and refine the
  description of the problem

3
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
• Plan for extensibility

4
Purpose of Modeling

• Testing a physical entity before building
• Communication with customer
• Visualization
• Reduction of complexity
• Better understanding of the problem

5
Early Modeling Notations

• Template-based natural languages
• SREM
• Boxes and arrows depicting data and control flow
• SADT, IDEF
• Statecharts
• Data Structures
• Jackson Design Notation

6
OO was the catalyst for newOO modeling techniques

• Many different contenders
• Grady Booch, Rational Software
• Jim Rumbaugh, GE, OMT
• Ivar Jacobsen, Ericsson, use cases
• Unified Modeling Language (UML)
• Combines Booch, Rumbaugh, Jacobsens techniques
• PL/1 of modeling languages

7
Object Modeling Technique (OMT)

• Three complimentary views of the system
• Object model (WHAT)
• Static, structural view of the system
• Describes objects in the system and their
  relationships

8
Object Modeling Technique (OMT)

• Dynamic model (WHEN)
• Temporal, behavioral, control view of system
• Interaction among objects
• Functional model (HOW)
• Transformational, function view of the system
• Describes the transformation of data

9
Object Model

• Object - a concept, abstraction, or thing
• Promote understanding of problem domain
• Object is distinguishable and has identity
• Class - group of objects with
• similar properties,
• common behavior
• common relationships to other objects
• common semantics

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Object Model (cont.)

• An object is an instance of a class
• Attribute - a data value associated with an
  object
• pure value, not an object
• Operation - a function or transformation that may
  be applied to or by an object

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Object Model (cont.)

• 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

• Synchronous instructional web tool
• Use the Web Browser as sophisticated data display
• Group-based communication model
• Reliable multi-cast communication protocol

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WEB Class Components

• 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.)

• Real audio stream
• Audio connection from the instructor to the
  students
• Live connection
• Chat tool
• Feedback mechanism from the students to the
  instructor

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Example Class Definitions
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

• 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
Communicates with
Mreceiver
Msender
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Object Model Aggregation

• Part-of relationship
• associates an object representing an assembly
  with the objects representing its components
• 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

• 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
Web_Instructor
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Object Model Multiplicities

• Indication how many instances of one class may
  relate to an instance of another class

Zero or more
One or more
3
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
Msender
ViewerConfig
Mreceiver
Browser_Wrapper
Browser_Listener
Helper_App
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Object Model Creation Tips

• Understand the problem
• Keep it simple (initially)
• Choose good class names
• Look for binary associations
• Ignore multiplicities (initially)

• Do not feel you have to use all the constructs
• Concentrate on WHAT
• Document, document, document!
• Refine until complete and correct