DBMS
A Database Management System (DBMS) is a set of computer programs that controls the creation, maintenance, stores, retrieve, define and manage data in a database.
Basic database concepts are important since GIS incorporates much of the functionality of DBMS.
A database is a collection of tables. Businesses and government agencies that serve large clienteles, such as telecommunications companies, airlines, credit card firms, and banks, rely on extensive databases for their billing, payroll, inventory, and marketing operations.
Database management systems are information systems that people use to store, update, and analyze non-geographic databases.
Geographic data are a special case: records correspond with places, not people or accounts. Columns represent the attributes of places. Database management systems are valuable because they provide secure means of storing and updating data.
DBMS provide transaction management functions that allow multiple users to edit the database simultaneously.
DBMS also provide sophisticated means to retrieve data that meet user-specified criteria. In other words, they enable users to select data in response to particular questions.
A question that is addressed to a database through a DBMS is called a query.
Database queries include basic set operations, including union, intersection, and difference.
The product of a union of two or more data files is a single file that includes all records and attributes, without redundancy.
An intersection produces a data file that contains only records present in all files.
A difference operation produces a data file that eliminates records that appear in both original files.
