Relational Database Model:
1) The relational database model is developed by “Edgar F. Codd” at IBM in 1970.
2) The relational Database Model used the basic concept of a relation or table.
3) A table is a collection of records and each record in a table Contains the same fields.
4) Every row or entity (called Tuple) must have a unique identification or key based
on the data.
5) The different tables may have the common column name (Attribute), but a single
table must not Contain multiple columns (Attributes) with the same name.
6) The relationship between the two tables is implemented using a common and
unique attribute in the tables.
7) Columns are attributes that belong to the entity modeled by the table.
8) order of rows (tuples/entity) and columns (attributes) is not important.
9) But every Tuple must be unique. It means that for every record or Tuple in a table
there is something that uniquely identified ¡t from any other Tuple.
10) Each cell can contains only single value (value for attribute).
1) The column (attribute) contains same types of values for every Tuple.
) The two tables in the database must not have the same name. they can have some
column name in common.
Relational Database Management System (RDBMS)
RDBMS is a software system that provides access to a relational database.
RDBMS ¡s based on relational database model introduced by E. F. Codd in 1970.
1) Generally a table with columns and rows is a relation.
2) All data and relationships are represented ¡n two dimensional table called a relation.
3) In other words, it represents the relation between rows and columns of a t
4) A relation consists of number of records or row-wise information and column-wise .
1) An attribute is a named column of a relation.
2) In the relational model, relations are used to hold information about the objects to
be represented in the database.
3) A relation is represented as a two-dimensional table in which the rows of the table corresponds to individual records and the table columns correspond to attributes.
4) Attributes can appear in any order and the relations will still be the same relations.
1) A domain is the set of allowed values for one or more attributes.
2) A domain defines the type of data represented by an attribute.
3) A domain is the set of all possible values that an attribute may validly contain.
4) Every attribute has some pre-defined value scope, known as domain.
5) For Example: in college database, domain for “Gender” column consists of one
two values “Male” and “Female”.
6) Similarly, domain for “CityName” column consists of range of valid city names of
student studying in the college from Amravati Division. (Domain of “CityName”
may includes “Amravati, Akola, Yavatmal, Washim, Buldhana).
7) Therefore every table that has a column “CityName” can contain only those values