The Object-Oriented Design Paradigm
an abstract framework for a set of items; example: "image"
an instance of a class; example: a specific image
property: a feature or attribute of the objects in a class;
usually has values; example: "size" (values: 1in x 1in, etc), "color"
(values: blue, red, etc)
an action that can be performed on objects of a class;
example: "save", "rescale"
event: an external event that happens to objects of a class and
can trigger methods to be invoked; example: "click on"
Class- or type-hierarchy
classes form a hierarchy based on the ISA relation
inheritance: classes inherit properties, methods and events
from their parents in the class hierarchy
two classes are in ISA relation if all objects of the first
class are also objects of the second class; for example:
vector-graphic ISA image; the ISA relation usually corresponds
to a normal English sentence using "is a"; for example:
"a vector graphic is an image"
the ISA relation must be distinguished from the HAS relation that
holds between objects and their properties; examples:
image HAS size, image HAS color
An example of object-oriented design is the document object model
(DOM) that describes elements of webpages (such as link, image,
table, text), their properties (target, name, font), their methods
(load, save) and their events (click on, mouse over).