3 - Logical Models and Query Languages

Abstract

This chapter is designed to review the logical models and query languages used in spatial database systems. The chapter describes how the representation and querying of geographic objects can be supported by the main categories of a database management system (DBMS), such as relational and object-oriented systems. A conceptual schema describes at an abstract level one or many themes necessary for representing the set of geographic objects existing in a geographic application as well as the relationships among them. The chapter introduces these reference schemas and lists a set of representative queries used in a spatial database based on these schemas. Abstract data types (ADT) were introduced as a way to circumvent the lack of modeling power inherent in the basic relational database model of a nonstandard database application. The idea behind this concept is to hide the structure of the data type from the user or the programmer, who can access it only through the operations defined on it. This type of split between use and implementation is called “encapsulation,” and it enables the programmer to extend a query language with geometric functionality independently of a specific representation or implementation. This chapter discusses important issues related to the design of spatial ADTs and describes a systematic approach to handling topological relationships among objects. The chapter also focuses on the representation of geographic objects and their manipulation by using an extended relational model as a support through both a structured query language (SQL) and an object-oriented framework.