Systems Analysis

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Systems Analysis

• Dr. V. Sridhar
• Associate Professor
• IT Systems Group
• Indian Institute of Management
• Lucknow

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Use Case Analysis Overview

• Use Case Analysis is performed by the Designer,
  once per iteration per use-case realization
• Supplement use-case specifications
• For each use-case realization
• Find Classes from use-case behaviour
• Distribute use-case behaviour to classes
• For each resulting analysis class
• Describe attributes and associations
• Describe responsibilities
• Qualify Analysis Mechanisms
• Unify Analysis Classes
• Checkpoints

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Use-Case Realisation

• A use-case realisation describes how a particular
  use-case is realized within the Design Model in
  terms of collaborating objects
• A use-case realisation in the Design Model can be
  traced to a use-case in the Use-case model
• Use-case realisation can be represented using
• Interaction Diagrams
• Sequence Diagrams and Collaboration Diagrams
• Class Diagrams

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Supplement Use-Case Descriptions

• The description of each use-case is not always
  sufficient for finding analysis classes and their
  objects
• Convert the use-case descriptions from
  black-box to white-box
• The system displays a list of course offerings
• The system retrieves and displays a list of
  current course offerings from the course catalog
  legacy database

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Class

• An abstraction
• Describes a group of objects with common
• Properties (attributes)
• Behavuior (operations)
• Relationships
• Semantics
• Emphasises relevant characteristics
• Suppresses other characteristics
• A class contains
• Class name, structure (attributes),
  behaviour(operations)

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Find Classes from Use-Case Behaviour

• The complete behaviour of a use-case has to be
  distributed to analysis classes
• Use of stereotypes
• Boundary, control and entity classes
• Analysis class represents an early conceptual
  model for things in the system which have
  responsibilities and behaviour
• Analysis classes handle primarily functional
  requirements
• The first step towards executables

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Boundary Class

• Intermediates between the interface and something
  outside the system
• One boundary class per actor/use-case pair

Register for Courses
Course Catalog System
student
CourseCatalogSystem
RegisterForCoursesForm
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Entity Class

• Key abstractions of the System
• Sources of inspiration
• Glossary
• Business Domain Model
• Use-case flow of events
• How to find Entity Classes?
• Underline noun clauses in the use-case flow of
  events
• Remove redundant candidates
• Remove vague candidates
• Remove actors
• Remove attributes and operations

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Candidate Entity Classes

• Register for Courses (Create Schedule)
• Definitions of Classes
• CourseOffering A specific course offering for a
  course, including days and times of the week
• Schedule The courses a student has selected for
  the current semester
• Student A person enrolled in classes at the
  University

Schedule
CourseOffering
Student
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Control Class

• Provides coordinating behaviour in the system
• One control class per use case

Register for Courses
Course Catalog System
student
RegistrationController
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Analysis Classes
Register for Courses
Course Catalog System
student
RegisterForCoursesForm
Schedule
CourseOffering
RegistrationController
Student
CourseCatalogSystem
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Distribute use-case Behaviour to Classes

• For each use-case flow if events
• Identify analysis classes
• Allocate use-case responsibilities to analysis
  clases
• Model analysis classes interactions in
  Interaction Diagrams

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Allocating Responsibilities to Classes

• Use analysis class stereotpes as guides
• Boundary Classes
• Behaviour that involves communication with an
  actor
• Entity Classes
• Behaviour that involves the data encapsulated
  within the abstraction
• Control Classes
• Behaviour specific to a use-case or part of a
  very important flow of events

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Anatomy of Sequence Diagrams
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Describe Responsibilities

• Statement of something an object can be asked to
  provide
• The actions that the object can perform
• The knowledge that the object maintains and
  provides to other objects

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Describe Attributes

• Attribute
• Used to store information
• Attribute name should be a noun that clearly
  states what information the attribute holds
• Description of the attribute should dscribe what
  information is to be stored in the attribute
• Sources for Attributes
• Domain knowledge, requirements, glossary, domain
  model, business model

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Describe an Association

• The semantic relationship between two or more
  classifiers that specifies connections among
  their instances

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More on Class Diagrams

• Association
• Structural relationship specifying that objects
  of one thing are connected to objects of another
• Navigation
• allows navigation from one kind of objects to
  another
• Unless specified navigation is bi-directional
• Arrowhead pointing to the direction of traversal
• Aggregation
• Model a whole/part relationship
• Represents has-a relationship
• Generalisation
• Relationship between general thing (super class
  or parent) and a more specific kind of a thing
  (subclass or child)
• Child is substitutable for the parent
• Direction from child to parent

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More on Class Diagram

• Composition
• Variations of simple aggregation
• Has strong ownership and coincident lifetime as
  part of the whole
• Subclasses once created, they live and die with
  the superclass
• Dependency
• Specifies that a change in the specification of
  one thing may affect another thing that uses it,
  but not necessarily the reverse
• Directed to the thing that is depended on

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Unify Analysis Classes

• Before design Analysis classes need to be
  filtered to ensure that a minimum number of new
  concepts have been created
• Merge classes that define similar behaviour
• Merge entity classes that define the same
  attributes aggregate the bahviour of merged
  classes
• Evaluate the results
• Verify that the analysis classes meet the
  functional requirements of the system
• Verify that the analysis classes and their
  relationships are consistent with the
  collaborations they support