Relational Database
Relational Database?
A relational database stores data in separate tables instead of placing all data in one large table.
A relational database then allows Data Base Administrator’s (DBA’s) to define relationships between these tables.
These relationships enable DBA’s to combine data from several tables for querying and reporting.
This is accomplished through the use of keys, which are database fields used to uniquely identify specific records in a table.
Relational database technology allows databases to be larger, faster, and more efficient.
The concept of a relational database was first developed by Dr. Edger F. (Ted) Codd in A Relational Model of Data for Large Shared Data Banks in 1970. Dr. Codd defined thirteen standards which must be met before a database can be considered to be a relational database:
A relational DBMS must be able to manage databases entirely through its relational capabilities.
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May 20, 2009 No Comments
Referential Integrity
Referential integrity is a database management safeguard that ensures every foreign key matches a primary key.
For example, customer numbers in a customer file are the primary keys, and customer numbers in the order file are the foreign keys. If a customer record is deleted, the order records must also be deleted; otherwise they are left without a primary reference. If the DBMS does not test for this, it must be programmed into the applications.
Referential integrity in a relational database is consistency between coupled tables. Referential integrity is usually enforced by the combination of a primary key or candidate key (alternate key) and a foreign key. For referential integrity to hold, any field in a table that is declared a foreign key can contain only values from a parent table’s primary key or a candidate key. For instance, deleting a record that contains a value referred to by a foreign key in another table would break referential integrity. A relational database management system (RDBMS) enforces referential integrity, normally either by deleting the foreign key rows as well to maintain integrity, or by returning an error and not performing the delete. Which method is used would be determined by the referential integrity constraint, as defined in the data dictionary.
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May 10, 2009 No Comments
