Computer Based Objects

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Computer Based Objects

• Object oriented programming

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Computer Based Objects

• The computer based objects are given a unique
  name, a set of attributes and a set of functions.

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Computer Based Objects
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Attributes

• Attributes are data items held by objects within
  a class. In the object model it is usual to
  distinguish between independent base attributes
  and dependent derived attributes.

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Operations or Methods

• An operation is a function that may be applied to
  objects or by objects within a class. A computer
  based object may be considered to consist of a
  set of hidden attributes which are only
  accessible via a set of associated functions,
  refer to figure 1.

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Object Modelling Technique

• Computer aided software engineering CASE tools
  are employed during the network modelling phase
  to ensure that the interrelationships between
  objects are correctly defined.

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Object Modelling Technique

• OMT was developed by Rambaugh at the Advanced
  Concepts Centre.
• Four steps
• Analysis
• System Design
• Object Design
• Implementation

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Analysis

• The analysis stage starts from a statement of the
  problem and goes on to build a model of the real
  system that incorporates all of its important
  properties.

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Analysis

• The model is described in terms of the
  application domain concepts and can easily be
  understood by experts who are not computer
  programmers.

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Analysis

• An important part of the analysis stage is to
  identify classes of real world objects and create
  corresponding classes of computer based objects
  which fully represent the real objects with all
  their complexity.

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System Design

• The system design stage is employed to determine
  the high level overall architecture of the system
  model.

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Object Design

• The purpose of the object design stage is to add
  implementation detail to the system model. Object
  classes are augmented with data structures and
  classes which are chosen to optimise system
  performance.

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Implementation

• During the implementation stage the object
  classes and relationships are translated into a
  programming language such as C or an object
  oriented database management system OODBMS.

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OMT

• The OMT method supports a graphical notation for
  representing object-oriented concepts.

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Object Classes

• An object class describes a group of objects
  with
• similar properties or attributes,
• common behaviour or operations,
• common relationships to other objects.

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Object Classes

• Objects are grouped into classes so that
  important definitions can be isolated. By
  grouping objects into classes the problem is
  abstracted.

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Object Classes

• Common definitions such as attributes and
  operations are defined once at a high level on
  the class hierarchy and are inherited by objects
  at a lower level. In this way all objects in the
  class benefit by the reuse of code.

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Inheritance and Generahsation

• Inheritance is a powerful abstraction for sharing
  similarities among classes whilst still
  preserving their differences. Inheritance is
  transitive across an arbitrary number of levels
  within the class hierarchy.

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Links and Associations

• Links and associations are used to establish
  relationships among objects and classes. A link
  is a physical or conceptual connection between
  object instances.

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Links and Associations

• A link is an instance of an association. An
  association describes a group of links with a
  common structure. Associations are inherently
  bi-directional.

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Aggregation

• Aggregation defines the part of relationship
  where objects representing components parts are
  associated with an entire assembly. An aggregate
  object is made of components which are part of
  the aggregate. Aggregation is a strong form of
  association.