In the previous article we’ve learned concerning function dependency and decomposition. During this section we’ll study regarding RELATIONAL ALGEBRA AND RELATIONAL CALCULUS. There are two official languages for the relational model : RELATIONAL ALGEBRA AND RELATIONAL CALCULUS. A data model must embrace a collection of operations to control the information , additionally to the info model’s construct for outlining database’s structure and limitations
DEFNITION :
The basic set of operations for the relational model is RELATIONAL ALGEBRA . These operations alter user to specify basic recovery requests. The result of retrieval is a new relation ,which may have shaped from one or additional relations. The algebra operations therefore turn out new relation which might be further operated by victimization operations of similar algebra. A sequence of relational algebra operations forms a relational algebra expression, whose result will also be a relation that represents the result of a database query.
IMPORTANCE:
- The relational Algebra is incredible vital for several reasons.
- Firstly it provides a formal foundation for relational model operations.
- Second, may be additional vital , it is use as a basis for implementing and optimizing queries in relational database management system.
- Third, number of ideas is within the SQL (structured query language) for RDBMSs.
RELATIONAL CALCULUS:
The relative calculus provides the next level declaration for describing relative queries. A relative calculus expression creates a replacement relation , which is describe in terms of variables that ranges over the rows of stored database relation (in tuple calculus).or over the columns of stored relations (in domain calculus) .
The relational algebra is contemplate as associate degree integral a part of the relative information model. There are varied operations under that. Its operation is divide into 2 teams . One group includes set operation from mathematical set theory . Set operations embrace UNION, INTERSECTION, SET DIFFERENCE AND CARTESIAN PRODUCT. The other group consists of operations developed specifically for relational databases, These other group include SELECT, PROJECT, and JOIN among others.
