Relational Database Management System (RDBMS)

      A relational database management system (RDBMS) is a database management system (DBMS) that is based on relational model. It is the information that is stored database is related to import and export information each other. It acts as an interface between the user and the data. It ensures that the data is kept in a compact and consistent format, and allow the user to ask a wide range of questions about the data. A DBMS can be described by the view of the data it presents to the user.

 Key terms used in RDBMS

Query: A query is a small command or program given to a database system instructing it how to manipulate some data from a database.

Example: SELECT * FROM tbl_std;

Relation: A relational database consists of a set of two-dimensional tables termed relations. All the data in the database is contained entirely within such tables. Each relation in the database has a unique name so that it can be identified.

Example: An example of relation is shown here. It relates the names of the students and the marks obtained by them.

Students name	Mathematics	Science
Jems	88	67
Nikki	68	69
Ram	82	87

Domain: A column of data from such a relation is called a domain. Thus a domain represents a "vertical slice “of a relation. Each domain in a relation has a unique name. A domain is constrained to hold one particular type of data.

Example: Using example of the above relation, the domain Mathematics is shown here.

Mathematics

88

68

82

Attribute: An attribute refers to a property of a particular domain, for instance its name. Another attribute is the type of data stored within that domain.

Example: In the above example of domain, the name of domain “Mathematics” and the data type i.e. “integer” is the attribute of that domain.

Tuple: A single row from a relation is termed a tuple. A tuple represents a "horizontal slice" of a relation.

Example: An example of single tuple from the above relation is shown below.

Students name	Mathematics	Science
Jems	88	67

Field: A single atomic item of data is termed a field. A field is represented by the intersection of a specific tuple with a specific domain.

Example: An example of single field from the above relation is shown below.

Jems

Schema: Schema defines the structure of a relation which consists of a fixed set of attribute domain pair.

Instance: An instance of a relation is a time varying set of tuples where each tuple consists of attribute value pairs.

Candidate Key: A candidate key is a set of attribute that form a super key but no proper subset of which is a super key.

Primary Key: A primary key is a candidate key chosen by database designer to identify tuples in a relation.