GIS functionality: an overview
This chapter considers objectives in database management and the components of database systems in general. It takes a broader view of data modelling, examining real-world conceptual models intended for database design and logical models oriented to particular types of Database Management System (DBMS). A widely used technique for building conceptual models is called entity relationship (EIR) modelling. The chapter introduces the subject of spatial query languages for Geographical Information Systems (GIS) applications. Updating of GIS databases can be complicated by the need to maintain several representations or versions of same geographical area, reflecting either real-world changes, or proposed changes, that may be part of development plans. The relational model is very much the most widely implemented for commercial applications and it is characterised by quite simple concepts of data organisation and related query languages. The shortcomings of standard facilities of a relational database have led to the use of special-purpose spatial indexing software used in parallel with standard facilities.