GIS, expert systems, and interoperability

ing the essential qualities that are useful for a given domain and grouping those objects with similar qualities is a powerful way of simplifying the computer representation of a problem. These essential qualities characterise the state and the behaviour of objects. Behaviour is defined by abstracting the essential operations that an object can perform and which can be performed on it. A vector class in an expert system, defines the state and behaviour of GIS vector layers. The state of a vector object includes the name of the GIS layer, its description, default colour and its physical location. Behaviour is described in methods which are associated with the vector class. These methods are routines which encapsulate the GIS commands to draw, delete, create, modify and manipulate GIS layers. The commands are hidden from the user who does not need to know how GIS operations are implemented. Encapsulation also serves to hide the complexities of GIS data representation. Objects inherit state and behaviour from parent classes. For example, a roads object, representing a GIS road network layer, inherits the state and behaviour of its parent