Evaluating GIS Vendor Templates

Object Models
Object models have the advantage of dealing with entities at a completely abstract level. Since an object can contain both the attributes and code to control its behavior, it is more intelligent than a relational entity. These attributes and behaviors are called properties and methods in object terminology. Another important characteristic of object oriented systems is their support of inheritance. An object can inherit the properties and methods of another object, and only focus on differences which make it unique from its parent. Several object notations existed before the mid-1990s, but most of them have been replaced with the standard Unified Modeling Language (UML). Some of the basic terminology and notation of the UML standard can be found below:

A class is a description of a set of objects that share the same attributes, operations, methods, relationships and semantics. A class may use a set of interfaces to specify collections of operations it provides to its environment. Classes can also be categorized into abstract and coclass types depending on their ability to create new objects and specify subclasses.

Object Classes are represented using the following notation:

Object Class

attributes
A method is the implementation of a service that is requested from an object. It specifies the algorithm or procedure that effects the results of the service.
Inheritance is the mechanism by which more specific elements incorporate structure and behavior of more general elements.
A property is a named value denoting a characteristic of an object. Properties of an object are shared by all the specific instances of the object.
A relationship defines the nature of the object class interaction. An n-ary association can exist between three or more classes. Some sample relationships are shown below:

This information is intended only as in introduction to the object modeling process. More information on object modeling and the complete UML specification can be found on the World Wide Web at http://www.rational.com/uml. [OMG, 1999]