Relational database
- 1. Relational Model in DBMS WELCOME TO DUCAT INDIA 7070905090 info@ducatindia.com
- 2. Relational Model in DBMS The relational database model derived from the mathematical concept of relation and set theory. It was proposed as a technique to data modeling by Dr Edgar F. Codd of IBM Analysis in 1970 in his document entitled “A Relational Technique of Information for Huge Shared Data Banks.” This document marked the start of the field of a relational database. The relational model is based on concept of a relationship that is physically defined as a table. In this model, tables are used to hold data about the object to be set in the database. A relation is defined as a two-dimensional table in which rows of the table correspond to single records, and the columns correspond to attributes. Each row is known as a tuple, and each column is known as an attribute.
- 3. Domain A domain is a collection of atomic values. Atomic defines that each value in the domain is hidden to the relational model. A domain is generally specified by name, data type, format, and constrained range of values. For example, as shown in figure attribute EMP-NO, it is a domain whose data type is an integer with a value ranging between 1, 00,000 and 2, 00, 00. Attributes are the properties that specify a relationship. For example, EMP-NO, NAME.
- 4. Attributes Attributes are the properties that prescribe a relation. For example, EMP-NO, EMP-NAME. Relation Schema The relation schema refers to the mechanism of a table. Example: EMPLOYEE (EMP-NO, EMP-NAME, DATE-OF-BIRTH, SEX, TEL-NO, and SALARY) is a relation schema for EMPLOYEE. If a schema has greater than one relation, it is known as Relational Schema. Tuple 106510 Rajesh Sharma 10-Feb- 1993 Male 9813245678 50,000 Each sequence in the relation is called a tuple. The relation includes 6 tuples, one of which is shown as:
- 5. Relation Instance The set of records of a relation at a specific instance of time is known as relation instance. The table shows the relation example of EMPLOYEE at a particular time. It can modify every time there is an insertion, deletion, or updating in the database. Degree The number of columns in the table is known as the degree of the relation. EMPLOYEE relation has degree 6. Cardinality The number of rows in a table is called the cardinality of the relation. EMPLOYEE relation has cardinality 6. NULL Values The value which is anonymous or not available is known as a NULL Value. It is described by blank space.