Database Relational Model

HISTORY OF RELATIONAL MODEL:

Relational model was 1st proposed by E.F.Codd

System R, then IBM developed it’s own DB known as DB2, then Oracle was created

Relation s actually the mathematical table.

RELATIONAL DATASTRUCTURES /STRUCTURAL PART OF

RELATION/ TERMINOLOGY

  1. Relation : a table wth Col & rows.
  2. Attribulte /fields : named column
  3. Tuple : row of relation/record
  4. Degree :num of att in a relation .if the colum/attr is only one then relation s of degree
  5. one also known as uniary . if a relation has two columns then it’s knowm as degree 2 also
  6. known as binary.
  7. Cardinality : num of rows (tuple) in a relation .
  8. Domain : data type .Set of allowable values for one or more att.
  9. Relational Db: collection of normalized relations.

PROPERTIES OF RELATION:

  1. Each table should have a distinct name.
  2. Each cell should have one value (atomic value).
  3. Attribute names should be unique.
  4. Values of an attr are from the same domain.
  5. Order of att has no significance.
  6. Each tuple should be distinct. Means no duplicate rows.
  7. Order of rows has no sigificance