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 : a table wth Col & rows.
- Attribulte /fields : named column
- Tuple : row of relation/record
- Degree :num of att in a relation .if the colum/attr is only one then relation s of degree
- one also known as uniary . if a relation has two columns then it’s knowm as degree 2 also
- known as binary.
- Cardinality : num of rows (tuple) in a relation .
- Domain : data type .Set of allowable values for one or more att.
- Relational Db: collection of normalized relations.
PROPERTIES OF RELATION:
- Each table should have a distinct name.
- Each cell should have one value (atomic value).
- Attribute names should be unique.
- Values of an attr are from the same domain.
- Order of att has no significance.
- Each tuple should be distinct. Means no duplicate rows.
- Order of rows has no sigificance