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by AB-Joel on September 11th, 2003

AB-Joel

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What makes a database "relational"?

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Answers. 2 helpful answers below.

  • by Mushen on November 18th, 2006

    Mushen

    There are 2 types of database:

    flatfile (everything is stored in one big table - like a telephone directory).

    Relational: 'Like' data is grouped together into seperate tables. Eg: A Library Database may have

    a table storing Customers Details
    a table storing Book Categories
    a table storing book details
    a table storing lending records

    The tables are related together using a Primary Key which is a unique identifier for each record. Eg: Books Table

    BookID (unique field)
    BookName text field

    A relational database minimises data errors, redundancy and duplication (each record should be stored only once (eg, when a book is lent to a customer, you would not want to have to enter the customer's details each time. Instead you store their details once in the Customers Table and then each time a book is lent to them, you look up the record required.

    Promotes data integrity (in other words the data stored is accurate) which means data storage costs are minimized.

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  • by theBengali on November 22nd, 2003

    theBengali

    In a relational database the data is arranged in relations which are
    nothing but conventional tables with some set of rules governing the
    arrangement of data within the table and among the tables. Any record
    or any row in a table is called an entity. And any value (or cell) in
    the row is called is called attribute.

    Now the set of rules (12 rules) governing the relational database
    are called Codd's rules (proposed by Dr. E F Codd in 1970 (?) ).

    To put things simple,
    a) An entity must have a unique set of attributes, that is, every row
    in a table must be unique.

    b) The referential integrity between two relations must be preserved.
    That is, if a record in a table A depends on a record in table B, then
    the database must detect and cancel any operation in table B that
    disturbs this integrity.

    e)Domain integrity must be preserved. That is, if there is a
    restriction for an attribute set (column) that its value
    should be within a predefined range then this restriction must apply
    in every insert/modification.

    d) Any value which is not supplied or unknown should be termed as null.
    A null value is not equal to empty syring ("") or zero. A null is even
    not equal to a null.


    e) Access to the database should be easy, but the ability of the user
    to view or modify the data should depend on permissions. The part of
    the database for which the user has no kind of permission is invisible
    to the user.

    To know further, read discussions on Codd's rules .

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