A computer database is a structured collection of records or data that is stored in a computer system. A database relies upon software to organize the storage of the data and to enable a person or program to extract desired information[1]. The term "database" refers to the collection of related records, and the software should be referred to as the database management system (DBMS); this is sometimes shortened to database manager or database system. Referring to the software as a database (as in "the OpenOffice database") is incorrect but not uncommon.

Typically, for a given data base, there is a structural description of the type of facts held in that database: this description is known as a schema. The schema describes the objects that are represented in the database, and the relationships among them. There are a number of different ways of organizing a schema, that is, of modeling the database structure: these are known as database models (or data models). The model in most common use today is the relational model. Other models such as the hierarchical model and the network model use a more explicit representation of relationships (see below for explanation of the various database models).

Database management systems are usually categorized according to the database model that they support. The data model tends to determine the query languages that are available to access the database. A great deal of the internal engineering of a DBMS, however, is independent of the data model, and is concerned with managing factors such as performance, concurrency, integrity, and recovery from hardware failures. In these areas there are large differences between products.

Contents [hide]
1 History
2 Database models
2.1 Hierarchical model
2.2 Network model
2.3 Relational model
2.3.1 Relational operations
2.3.2 Normal forms
2.4 Post-relational database models
2.5 Object database models
2.6 Semantic model
3 Database internals
3.1 Storage and physical database design
3.1.1 Indexing
3.2 Transactions and concurrency
3.3 Replication
3.4 Security
3.5 Locking
3.6 Architecture
4 Applications of databases
5 Database as Cultural Form
6 Database development platforms
7 References
8 See also



[edit] History
The earliest known use of the term data base was in November 1963, when the System Development Corporation sponsored a symposium under the title Development and Management of a Computer-centered Data Base[2]. Database as a single word became common in Europe in the early 1970s and by the end of the decade it was being used in major American newspapers. (The abbreviation DB, however, survives.)

The first database management systems were developed in the 1960s. A pioneer in the field was Charles Bachman. Bachman's early papers show that his aim was to make more effective use of the new direct access storage devices becoming available: until then, data processing had been based on punched cards and magnetic tape, so that serial processing was the dominant activity. Two key data models arose at this time: CODASYL developed the network model based on Bachman's ideas, and (apparently independently) the hierarchical model was used in a system developed by North American Rockwell later adopted by IBM as the cornerstone of their IMS product. While IMS along with the CODASYL IDMS were the big, high visibility databases developed in the 1960s, several others were also born in that decade, some of which have a significant installed base today. Two worthy of mention are the PICK and MUMPS databases, with the former developed originally as an operating system with an embedded database and the latter as a programming language and database for the development of healthcare systems.

The relational model was proposed by E. F. Codd in 1970. He criticized existing models for confusing the abstract description of information structure with descriptions of physical access mechanisms. For a long while, however, the relational model remained of academic interest only. While CODASYL products (IDMS) and network model products (IMS) were conceived as practical engineering solutions taking account of the technology as it existed at the time, the relational model took a much more theoretical perspective, arguing (correctly) that hardware and software technology would catch up in time. Among the first implementations were Michael Stonebraker's Ingres at Berkeley, and the System R project at IBM. Both of these were research prototypes, announced during 1976. The first commercial products, Oracle and DB2, did not appear until around 1980. The first successful database product for microcomputers was dBASE for the CP/M and PC-DOS/MS-DOS operating systems.