Page 168 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Object Oriented Analysis and Design

Notes 13.2.4 Public Protocol Layer: External

Items in this layer define the functionality of the object. Here are some things to keep in mind
when designing class protocols: Good design allows for polymorphism. Not all protocol should
be public; again apply design axioms and corollaries 1.

Notes The following key questions must be answered: What are the class interfaces and
protocols? What public (external) protocol will be used or what external messages must
the system understand? What private or protected (internal) protocol will be used or what
internal messages or messages from a subclass must the system understand?

Task Analyze the difference between protected protocol layer and public protocol
layer.

13.2.5 Designing Classes: Refining Attributes

Attributes identified in object-oriented analysis must be refined with an eye on implementation
during this phase. In the analysis phase, the name of the attribute is enough. But in the design
phase, detailed information must be added to the model.

Attribute Types

The types of attribute are explained as below:

1. Single value attributes: Single value attributes consists of just one value or state.

Example: Name, address, salary.

2. Multiplicity or multi value attributes: Multiplicity or multi value attributes can have a
collection of several values at a time.

Example:
(a) To list the students who have scored above 710 marks.

(b) If we want to keep record of the names of people who have called a customer
support line for help.

3. Instance connection: It is reference to another object. It offers the mapping required by an
object to accomplish its responsibilities.

Example: A person may have more than one account. A person has zero to many instance
connections to Account(s). Similarly, an Account can be assigned to one or more person(s) (joint
account). So an Account has zero to many instance connection to Person(s).

162 LOVELY PROFESSIONAL UNIVERSITY