Introduction To Relational Data Model

Today, almost 75% to 85% applications that are developed, deal with some type of data and database one or other way. Every other second, huge amount of data is gathered over the net and through various devices all over the world. This data help companies in keeping track of their business processes (such as order processing, shipping information & customer information/relationship management etc.), manage information effectively and in turn help them grow.

It is almost impossible to go on storing such a huge amount of information without managing it in a proper way. In order to manage and store the information/data in the storage/database, there are various methods and models that are developed. One such model is Relational Database Model, which has proved to be the best data management model.

As a simple explanation, relational data model allows various data packets/files to be related to each other with a set of relations (Please do not confuse this relation with normal linking of two files). For example, if customer names are stored in one file ‘CUSTOMER’, and other file contains the names of cities ‘CITY’. Then CUSTOMER file can have a relation with CITY, which will help identify which city the customer belongs to. (Please note that this is just a simple example of relational database and even when it does portrait the power of relational database, it still does not say everything about it)

Devised by Edgar F. Codd, the relational data model is entirely based on the predicate logic and set theory of mathematics. Codd used mathematical n-ary relations as a base to represent data, which is a subset of the Cartesian product of n sets. These sets are bound to each other in a structured manner with various constraints (i.e. relations). The data, as mentioned above is managed by using relational calculus and various constraints to form a container that hold it (which is also known as schema), the relation between data can be expressed in a particular structured language.

The data is arranged in a relation which is visually represented in a two dimensional table. The data is inserted into the table in the form of tuples (which are nothing but rows). A tuple is formed by one or more than one attributes, which are used as basic building blocks in the formation of various expressions that are used to derive a meaningful information. There can be any number of tuples in the table, but all the tuple contain fixed and same attributes with varying values.

The relational model is implemented in database where a relation is represented by a table, a tuple is represented by a row, an attribute is represented by a column of the table, attribute name is the name of the column such as ‘identifier’, ‘name’, ‘city’ etc., attribute value contains the value for column in the row, constraints are applied to the table and form a logical schema.

In order to facilitate the selection of a particular row/tuple from the table, the attributes i.e. column names are used, and to expedite the selection of the rows some fields are defined uniquely to use them as indexes, this helps in searching the required data as fast as possible.

All the relational algebra operations, such as Select, Intersection, Product, Union, Difference, Project, Join, Division, Merge etc. can also be performed on the Relational Database Model. Operations on the Relational Database Model are facilitated with the help of different conditional expressions, various key attributes, pre-defined constraints etc. For example: selection of information of the customer, who is living in some city for more than 20 years.

Following are few terms used in relational database model:

Candidate Key: Any field or a combination of fields that identifies a record uniquely is called a Candidate Key. The Candidate Key cannot contain NULL value and should always contain a unique value.

Primary Key: Primary key is nothing but a candidate key that identifies a record uniquely.

Foreign Key: A Foreign key is a primary key for other table, in which it uniquely identifies a record. A Foreign Key defines relation between two (or more) tables. A Foreign key can contain NULL value.

Constraints: Constraints are logic rules that are used to ensure data consistency or avoid certain un-acceptable operations on the data.