Relational Algebra
RELATIONAL ALGEBRA
Query Language It is a Language in which a user request information from the database. These languages are typically of a level higher than that of the standard programming language. It is divided into either procedural or non-procedural language. In the procedural Language, the user instructs the system to perform the sequence of operation on the database to compute a desired result. In a non-procedural Language, the user describes the information desired without giving a specific procedural for obtaining the information.
Relational Algebra Definition
It is a procedure language. It consists of a set of operations that take one or more relations as input and produce a new relation as a result. The fundamental operations of relational algebra are select, project, union, set difference, Cartesian product and rename. Other operations are: Set intersection, natural join, division and assignment. • The basic set of operations for the relational model is known as the relational algebra. These operations enable a user to specify basic retrieval requests. • The result of retrieval is a new relation, which may have been formed from one or more relations. The algebra operations thus produce new relations, which can be further manipulated using operations of the same 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 (or retrieval request).
Keys • Let K ( R where K is a superkey of R if values for K are sufficient to identify a unique tuple of each possible relation r(R) – by “possible r” we mean a relation r that could exist in the enterprise we are modeling. – Example: {customer-name, customer-street} and {customer-name} are both superkeys of Customer, if no two customers can possibly have the same name. • K is a
Query Language It is a Language in which a user request information from the database. These languages are typically of a level higher than that of the standard programming language. It is divided into either procedural or non-procedural language. In the procedural Language, the user instructs the system to perform the sequence of operation on the database to compute a desired result. In a non-procedural Language, the user describes the information desired without giving a specific procedural for obtaining the information.
Relational Algebra Definition
It is a procedure language. It consists of a set of operations that take one or more relations as input and produce a new relation as a result. The fundamental operations of relational algebra are select, project, union, set difference, Cartesian product and rename. Other operations are: Set intersection, natural join, division and assignment. • The basic set of operations for the relational model is known as the relational algebra. These operations enable a user to specify basic retrieval requests. • The result of retrieval is a new relation, which may have been formed from one or more relations. The algebra operations thus produce new relations, which can be further manipulated using operations of the same 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 (or retrieval request).
Keys • Let K ( R where K is a superkey of R if values for K are sufficient to identify a unique tuple of each possible relation r(R) – by “possible r” we mean a relation r that could exist in the enterprise we are modeling. – Example: {customer-name, customer-street} and {customer-name} are both superkeys of Customer, if no two customers can possibly have the same name. • K is a