Relational model in DBMS
- The relational model uses a collection of tables to represent both data and the relationships among those data. Each table has multiple columns, and each column has a unique name.
- 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.
- The relational model represents the database as a collection of relations. Informally, each relation resembles a table of values or, to some extent, a flat file of records
- It is called a flat file because each record has a simple linear or flat structure.
- However, there are important differences between relations and files, as we shall soon see.
- When a relation is thought of as a table of values, each row in the table represents a collection of related data values
Properties of relations
Properties of database relations are:
- relation name is distinct from all other relations.
- each cell of relation contains exactly one atomic (single) value.
- each attribute has a distinct name.
- values of an attribute are all from the same domain.
- order of attributes has no significance.
- each tuple is distinct; there are no duplicate tuples.
- order of tuples has no significance, theoretically.