Database Concepts

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Databases have been in use since the earliest days of electronic computing, but the vast majority of these were custom programs written to access custom databases. Unlike modern systems which can be applied to widely different databases and needs, these systems were tightly linked to the database in order to gain speed at the price of flexibility.

In 1960, Charles Bachman developed the first database management system (DBMS) which two key data models arose: the network model (developed by CODASYL) followed by the hierarchical model (as implemented in IMS). These were later usurped by the relational model, which was contemporary with the so-called flat model designed for very small tasks. Another contemporary of the relational model is the object-oriented database (OODB).

Flat model

The flat (or table) model consists of a single, two-dimensional array of data elements, where all members of a given column are assumed to be similar values, and all members of a row are assumed to be related to one another. For instance, columns for name and password might be used as a part of a system security database. Each row would have the specific password associated with a specific user. Columns of the table often have a type associated with them, defining them as character data, date or time information, integers, or floating point numbers. This model is the basis of the spreadsheet.

Relational Database Model

Dr. Edgar F. Codd worked at IBM in San Jose, California, were he worked primarily in the development of hard disk systems. He was unhappy with the navigational model of the Codasyl approach, notably the lack of a "search" facility which was becoming increasingly useful when the database was stored on disk instead of tape. In 1970, he wrote a number of papers that outlined a new approach to database construction and eventually culminated in the groundbreaking paper called "A Relational Model of Data for Large Shared Data Banks".

In this paper he described a new system for storing and working with large databases. Instead of records being stored in some sort of linked list of free-form records as in Codasyl, Codd's idea was to use a "table" of fixed-length records. A linked-list system would be very inefficient when storing "sparse" databases where some of the data for any one record could be left empty. The relational model solved this by splitting the data into a series of tables, with optional elements being moved out of the main table to where they would take up room only if needed.

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