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A DBMS is a software program that typically operates on a database server or mainframe system to manage structured data, accept queries from users, and respond to those queries. A typical DBMS has the following features:

• Provides a way to structure data as records, tables, or objects


• Accepts data input from operators and stores that data for later retrieval


• Provides query languages for searching, sorting, reporting, and other "decision support" activities that help users correlate and make sense of collected data


• Provides multiuser access to data, along with security features that prevent some users from viewing and/or changing certain types of information


• Provides data integrity features that prevent more than one user from accessing and changing the same information simultaneously


• Provides a data dictionary (metadata) that describes the structure of the database, related files, and record information

Most DBMS systems are client/server based and operate over networks. The DBMS is an engine that typically runs on a powerful server or cluster of servers, in a SAN (storage area network) environment or mainframe with a high-performance channel to a large data store. The DBMS accepts requests from clients that may require sorting and extracting data. Once the server has processed the request, it returns the information to the client.

There are a variety of back-end database systems, clients, and methods of access. Database middleware products are designed to provide a middle layer of software that hides the differences among databases. ODBC (Open Database Connectivity), originally designed by Microsoft, has been one of the most popular middleware products. The section "Database Connectivity" later in this topic discusses middleware. Also see the topic "Middleware and Messaging."

The common language for accessing most database systems is SQL (Structured Query Language), which is discussed under the main SQL heading, "SQL (Structured Query Language)." Z39.50 is an open ANSI standard that allows database searching and information retrieval among networked systems. See "Z39.50."

Metadata is information that describes data in a database. A raw data file would appear as a mass of letters, numbers, and symbols; but by knowing the format and structure of how that data is stored, you can display the data as records, fields, attributes, and elements with specific rules and properties (i.e., some fields are locked or the data is displayed a certain way). A metadata file provides this knowledge. Recall the Mars spacecraft that burned up in Mars orbit. The company that built the spacecraft was working with acceleration data in English units of pounds of force. NASA entered the data into a computer that assumed metric units called newtons. This was a tragic metadata error, in which the description of the data was misinterpreted. See "Metadata" for more information.

Most databases are operational databases, meaning that data going into the database is used in real time to support the ongoing activities of a business. A point-of-sale business accounting system is an example. As items are sold, the inventory database is updated and the inventory information is made available to the sales staff. The invoicing, order entry, and related systems are also updated.

Data analysts use OLAP (online analytical processing) systems to analyze database information in order to find trends or make business decisions. A data warehouse is a large-scale OLAP and/or data mining system that is specifically designed to extract, summarize, combine, clean up, and process information from a number of data sources-such as the operational databases, legacy (historical) databases, and online subscription databases-for the purpose of analysis. Metadata is especially important in this environment. See "Data Warehousing" for more information.