Relation model concept and it's advantage & disadvantage

    Relation model concept and it's advantage & disadvantage

    1.         What is relational model?

  Ø Relation model represent database as a collection of relations. A relation is nothing but a table of values. Every row in the table represents a collection of related data values. This row in the table denotes a real world entity or relationship.

     Relational model concept: -

  ·     Attribute: - Each column in a table, Attributes is the properties which define a relation. Example: - DNO, DNAME.

  ·     Table: - In the relational model relations are saved in the table format. A table has two properties rows, column. Rows represent records and column represents attributes.

  ·     Degree: - The total number of attribute which in the relation which called the degree of relation.

  ·     Cardinality: - Total number of rows present in the table.

    Attribute domain: - Every attribute has some predefined values and scope which is known as attribute domain.

     Advantage of relational model: -

    1)       Simplicity: - A relational data model is simpler than hierarchical model and network model.

    2) Easy to use: - The relational model is easy as table consisting of rows and column is quite natural and easy to understand.

    3)       Data independence: - the structure of a database can be changed without having to change any application.

    4)   Query capability: - It make possible for a high level query language like SQL to avoid complex data navigation.

      Disadvantage of using relational model: -

   ·     Few relational databases have limits on field length which cannot be exceeded

   ·     Relational databases can sometime become complex as the amount of data grows and the relation between pieces of data become more complicated.     

     ·     Complex relational database may lead isolated databases where information cannot be shared from one system to another.