Significance of the Model's Components

We consider the classification of the geographic objects into container and non-container features as a semantically significant aspect of our model. While such a classification seems conceptually simple, it plays an important role in route finding problem. Under are the two characteristics of these classes:

• A container object at a particular level in the hierarchy can contain not more than one other container object, and the container object must be of a different type than the container. Thus a prefecture directly contains cities and indirectly contains neighbourhood, etc. However a prefecture does not contain another prefecture.
• A container object at a particular level in the hierarchy can contain one or more non-container objects, and the contained objects may be of different types of as long as they are not also contained by other container object. Thus, a prefecture contains a prefecture road and prefecture segment of highways, etc.

There are two benefits of this arrangement:

1. The hierarchy that results corresponds to ``user perspective level''. Thus, a user can have ``country level'' perspective, ``prefecture level'' perspective, etc. Therefore the route finder system, first, will determine the user perspective level and then process according to that level.
2. One possible query that may be posed in route finder system is: ``Retrieve all the major roads in prefecture X.'' To process such a query, the processor can potentially check each link $l_i$ in road network and use some another algorithm to decide whether it lies in prefecture X or not. This leads to inefficiency of the route finder system. Processing this type of query can be made more efficient, by using a geographic containment hierarchy in our model. Since each container object contains roads entirely contained in it and these contained roads have, also, been divided into different types therefore, the system can find the major roads in prefecture X by just invoking the method GetMajorRoads() defined in prefecture class. Hence there is no need to check each link $l_i$ to be in prefecture X and of type major road. This arrangement greatly reduces the computation time and is more efficient in terms of route finding performance.