The notions of database (DB) and database management system (DBMS) are well known. On the basis of DBMS different information and informating-controlling systems, used in all spheres of human activities are built. The corresponding DB may contain any data, however, in most cases this data is alphanumeric (that is text) or numeric. The common DB representation is an interconnected set of tables. Every table is made of rows (records) and columns (fields). Every record contains information on some object, every field contains the value of some property of the object. The simplest case is when all DB is made of one table. As an example, we can take a list of enterprise employees where every line contains data about one employee, and surname, first name, age, position, salary, etc. are the field values. Such data is usually called attributive, or to make it simple – table data.
The main operations that can be performed with table data include data search on different requests, ordering data (for example, by alphabet), joining interconnected data from different tables, calculation of total values, making different reports. Besides, DBMS enables performing operations for creating and modifying DB: adding and removing records, editing (that is, changing values) record fields, changing records structure (adding and removing fields, etc.).
Usual (table) DBMS turn to be almost useless when working with such specific data type as spatial features.
A feature is characterized by its coordinates in some coordinate system (for example, geographic one). A feature is assigned at least by one pair of coordinates (X,Y) determining the point of its location. Besides, a feature may have a certain form and size which can be assigned by a set of coordinates of typical points. Buildings, parcels, pillars, wells, roads, reservoirs, nature zones, administrative districts, countries, etc. are examples of features.
Naturally, coordinates of feature points can be considered to be table data and stored in a standard DB. However, such an approach does not solve the tasks where the spatial character of features is particularly important. These tasks include, in the first place, feature displaying on a screen or printer, spatial search (that is, the answer to the question “What features are located in this point?”), calculation of spatial feature characteristics (length, area), visual feature editing, and also various tasks of spatial analysis.
A database designed to store information about features is called geoinformation database (GDB).
The content of GDB is not limited by feature coordinates. First of all, features can be classified by types, spatial characteristics, purpose and other criteria. So, it means that GDB should have a certain structure reflecting this classification. Besides, with each feature some table information may be linked. For example, features which represent buildings – address, living space, number of storeys, the owner, repairs date and other characteristics can be specified. This information should also be stored in GDB. Table data can be used for formulating requests (for example, “find all two-storeyed buildings”) and for controlling feature display (“paint buildings with different color shades depending on the number of storeys”). It is clear that programs intended to work with GDB should have a big set of operations with features apart from functions characteristic of standard DBMS. The conclusion to the above may be made in the following definitions:
Geoinformation database (GDB) is an organized set of spatial and table data which describes some territory and features located on it.
Geographic information system (GIS) is a program system intended for storing, processing and displaying data, stored in GDB.
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