System Analyst and Design

1
Structural Modeling

• Basics

2
What is Structural Modeling?

• The goal of the analyst to discover the key data
  contained in the problem domain and to build a
  structural model of the object.
• One of the primary purpose of the structural
  model is to create a vocabulary that can be used
  by the analyst and the user.
• Structural models represent the things, idea, or
  concepts-that is, the objects-contained in the
  domain of the problems.

3
Class

• A class is a general template that we use to
  create specific instances, or objects, in the
  problem domain.
• An attribute of an analyst class represents a
  piece of information that is relevant to the
  description of the class within the application
  domain of the problem being investigated.
• An attribute contains information the analyst or
  user feels the system should store.
• An operation or service describe the action to
  which the instances of the class are capable of
  responding.

4
Relationship

• Can be classified into three basic categories of
  data...
• Generalization
• Aggregation (collection of parts)
• Association
• The generalization enables the analyst to create
  classes that inherit attributes and operations of
  other classes. (a-kind-of)
• The aggregation relate parts to wholes or parts
  to assemblies. (a-part-of)
• The association is an organization with a common
  purpose and having a formal structure.

5
Object Identification

• The four common approaches are...
• Textual analyst
• Brainstorming
• Common object lists
• Patterns
• Textual analyst is an analyst of the use-case
  description. The text is examined to identify
  potential objects, attributes, operations, and
  relationships.
• Brainstorming is a process of a set of
  individuals sitting around a table and suggesting
  potential classes that could be useful for the
  problem under consideration.

6
Object Identification

• Common object list is simply a list of objects
  common to the business domain of the system.There
  are several categories.
• Tangible things (physical)
• Incidents (events)
• Roles (people)
• Interaction (communication)

7
Object Identification

• Other types of objects are...
• Places
• Containers
• Organizations
• Business records
• Catalogs
• Policies

8
Object Identification

• Patterns is simply a useful group of
  collaborating classes that provide a solution to
  a commonly occurring problem.

9
CRC Cards

• Class-Responsibility-Collaboration cards are used
  to document the responsibilities and
  collaborations of a class.
• Responsibilities of a class can be broken into
  two separate types Knowing and Doing
• Knowing are things that an instance of a class
  must be capable of knowing.
• Doing are things that an instance of a class must
  be capable of doing.
• Most use cases involve a set of several classes.
  Theses classes form Collaborations.

10
CRC Cards

• Collaborations allow analyst to think in terms of
  client, server and contracts.
• A client object is an instance of a class that
  sends a request to an instance of another class
  for an operation to be executed.
• A server object is the instance that receives the
  request from the client object.
• A contract formalizes the interaction between the
  client and the server objects.
• CRC Questions for Role Playing
• Who or what are you?
• What do you know?
• What can you do?

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Elements of a CRC Card

• The front of the card contains
• Class name (common noun)
• ID
• Type
• Description
• Associated use cases
• Responsibilities
• Collaboration

• The back of the card contains
• Attributes (Knowing Responsibilities of each
  class)
• Relationships ( generalization, aggregation and
  association)
• CRC cards are used to document the essential
  properties of a class.

12
Role-Playing CRC Cards with Use-Cases

• CRC cards can be used in a role-playing exercise
  that can be useful in discovering additional
  objects, attributes, relationships and
  operations.
• The first step is to review the use-case
  description.
• The second step is to identify the relevant roles
  that are to be played.
• The third step is to role-play scenarios of the
  use case.
• The forth step is to simply repeat steps 1
  through 3 for the remaining use cases.

13
Class Diagrams

• A class diagram is a static model that shows the
  classes and the relationships among classes that
  remain constant in the system over time.
• The class refer to the people, places and things
  about which the system will capture information.
• Attributes are properties of the class about
  which we want to capture information.
• Derived attributes are attributes that can be
  calculated or derived.
• The visibility of an attribute can be can be
  public (), protected () or private (-).
• Public not hidden from any objects
• Protected hidden from all except its immediate
  subclasses
• Private hidden from all classes

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Class Diagrams

• Operations are actions that a class can preform.
  The functions that are available to all classes
• Create new instance
• Return a value for a particular attribute
• Set a value for a particular attribute
• Delete an instance

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Class Diagrams

• There are four kinds of operations that a class
  can contain
• Constructor operation creates a new instance.
• Query operation makes information about the state
  of an object available to other objects.
• Update operation changes the value of some or all
  the object's attributes.
• Destructor operation simply deletes or removes
  the object from the system.

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Class Diagrams

• A primary purpose of a class diagram is to show
  the relationships, or associations, that classes
  have with one another.
• When multiple classes share a relationship, a
  line is drawn and labeled with either the name of
  the relationship or the roles that the classes
  play in the relationship.
• Multiplicity documents how an instance of an
  object can be associated with other instances.
• Association class is formed when classes share
  many-to-many relationships, which has its own
  attributes and operations.

17
Class Diagrams

• A generalization association shows that one class
  (subclass) inherits from another class
  (superclass).
• An aggregation association is used when classes
  actually comprise other classes.
• Aggregation is used to portray logical a-part-of
  relationships.
• Composition is used to portray a physical part of
  relationships.
• Physical implies that the part can be associated
  with only a single whole.