[Chapter 6]: Review Questions

Question 1: What is object-oriented analysis, and what are some advantages of using this technique?
O-O (Object-Oriented) analysis describes an information system by identifying things called objects that combine data and processes with the use of various O-O diagrams depicting system actors, methods and messages.
Advantages:
Integrates easily with O-O programming languages.Code is modular and reusable, which can reduce costs and development times.Easy to maintain and expand as new objects can be cloned using inherited properties.Disadvantages:
Somewhat newer method might be less familiar to development team members.Interaction of objects and classes can be complex in larger systems.
Question 2: Define an object and give an example.
An object represents a real person, place, event or transaction and possesses characteristics called properties (which the object either possesses on it's own or inherits from it's class) and attributes (which are the characteristics that describe the object).
For example: When a patient makes an appointment to see a doctor, the patient is an object, the doctor is an object and the appointment is an object.

Question 3: Define an attribute and give an example.
An attribute is a single characteristic or fact about an entity. An attribute, or field, is the smallestpiece of data that has meaning within an information system. In an O-O analysis, an attribute is part of a class diagram that describes the characteristics of objects in the class, also known as a data element. For example if you own a car, it has attributes such as make, model and colour.

Question 4: Define a method and give an example.
Methods are tasks or functions that the object performs when it recieves a message or command to do so, it describes what and how an object does something. For example your car performs a method "operate wipers" when you send a message by moving the relevant control.

Question 5: Define an encapsulation and describe the benefits that it provides.
Encapsulation is the idea that all data and methods are self-contained, and is an example of the black box concept. A black box does not want or need outside interferance. By limiting access to internal processes, an object prevents it's internal code from being altered by another object or process. Encapsulation allows objects to be used as modular components anywhere in the system, because objects send and recieve messages but do not alter the methods of other objects.

Question 6: Define polymorphism and give an example.
Polymorphism is the concept that a message gives different meanings to different objects.

For example the message "good-night" signals to a parent to read a bed time story to the child, however the same message to a dog tells the dog to sleep. The "good-night" message to the child signifies that it should get ready for bed.

Question 7: Define a class, subclass and superclass; give examples.
Obecjts belong to a group or cateogry called a class., and all objects within the class share common attributes and methods; it is a term used in O-O modelling to signify a group of similar objects.
A subclass is a further division of objects in a class. Subclasses are more specific categories in a class. For example, a truck is a subclass of the vehicle class, along with other subclasses such as car, mini-van, bicycle, etc.
A superclass is a more generalised category to which objects may belong. For example, a novel class belongs to a superclass called "books" because all novels are books.

Question 8: Define an actor and give an example.
An actor is an external entity with a specific role. In a use case model, actors are used to model interaction with the system. For example an actor would represent a customer in a simple use case diagram for a credit card transaction in a sales system.

Question 9: Define a use case and a use case diagram; give examples.
A use case represents the steps in a specific business function or process in UML (Unified Modelling Language). an external entity, called an actor, intiates a use case by requesting the system to perform a function or process. For example, in a medical office system, a patient (Actor) can make an appointment (Use Case).
A use case diagram is a visual summary of several related use cases within a system or sub-system. For example, consider a small auto-service department; the service department involves customers, service writers who prepare work orders and invoices, and mechanics who perform the work.

Question 10: Define the term black box and explain why it is an important concept in object-oriented analysis.
Black box is a metaphor for a process or action that produces results in a non-transparent or non-observable manner. In DFD's, a process will appear as a black box where the inputs, outputs and general funtion of the process are known but the underlying details are not shown. You can view an object as a black box because a message to the object triggers changes within the object without specifying how the changes must be carried out.

A petrol bowser is an example of a black box; when you select premium at the pump you do not think about how it selects the right fuel or determines the correct price, so long as it is done properly