The presence of a well-defined structure is a necessary condition for effective work with any big and complex block of data, including geoinformation database.
In most complex data structures it is possible to single out some main parts which are called components of the upper (first) level of this system. Components of the first level, in their turn, can be rather complex and may contain components of the second level and so on. A set of system components of all the levels makes up the hierarchical structure of this system.
For those GDB which are created and processed by means of GIS ObjectLand there are eight main types of the upper level components. In this chapter you will find brief description of these components. In next chapters they will be described in detail.
