relational model

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relational model

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relational database

A database that maintains a set of separate, related files (tables), but combines data elements from the files for queries and reports when required. The concept was developed in 1970 by Edgar Codd, whose objective was to accommodate a user's ad hoc request for selected data. Most every business database management system (DBMS), including Oracle, DB2, SQL Server, MySQL, etc., is a relational DBMS (RDBMS) (see DBMS).

Hierarchical, Network and Object Databases
In non-relational "hierarchical" and "network" databases, records in one file contain embedded pointers to the locations of records in another, such as customers to orders and vendors to purchases. These are fixed links set up ahead of time to speed up daily processing. Another type of non-relational database is the "object database," which stores data consistent with their object model (see object database).

Comparing and Joining
Routine queries to a relational database often require data from more than one file. For example, to obtain the names of customers who purchased a particular product, data must be extracted from both the customer and order files. A relational DBMS has the flexibility to "join" two or more files by comparing key fields such as account number and name and generating a new file from the records that meet the matching criteria (see join).

Indexes Are Used
In practice, a pure relational query can be very slow. In order to speed up the process, indexes are built and maintained on the key fields used for matching. Sometimes, indexes are created "on the fly" when the data are requested.

Relational Terms       Common Term

  Table or Relation      File

  Row or Tuple           Record

  Column or Attribute    Field



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References in periodicals archive ?
As long as such a numbers-only state is true, then fact tables fall into the above mentioned condition of having a granularity defined by the composite primary key containing the individual foreign keys into the dimension tables.
Or in a subtler alteration, many objects are defined with the Company Code and then an Object ID used in combination to define a composite Primary Key.
Primary key can be divided into natural primary and primary key natural primary key by the entity attribute of the natural primary key can be a compound in the form a composite primary key primary key columns cannot too much composite primary key complicates Join operation also increased the size of the external key table primary key is key in the absence of appropriate nature or nature complex or high sensitivity in human form.

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