Keys - relational database integrity, Database Management System

Assignment Help:

Candidate Key:  In a relation R, a candidate key for R is a subset of the set of attributes of R, which have the differnt two properties:

(1)        Uniqueness:                No two distinct tuples in R have the similar value for the candidate key

(2)        Irreducible:                 No correct subset of the candidate key has the uniqueness property that is the candidate key.

Each relation must have at least one candidate key which cannot be reduced more. Duplicate tuples are not permitted in relations. Any candidate key can also be a composite key. For instance, (student-id + course-id) together can create the candidate key of a relation known as marks (student-id, course-id, marks).

Let us review the properties of a candidate key.

Properties of a candidate key

  • A candidate key has to be unique and irreducible
  • A candidate might be involving one or more than one attributes. A candidate key that contains more than one attribute is said to be composite.

But why are we interested in candidate keys?

Candidate keys are essential because they give the basic tuple-level identification mechanism in a relational system.

For instance, if the enrolment number is the candidate key of a STUDENT relation, then the solution of the query: "Find student details from the STUDENT relation having enrolment number A0123" will output at most one tuple.


Related Discussions:- Keys - relational database integrity

A file manipulation command that extracts some records, A file manipulation...

A file manipulation command that extracts some of the records from a file is called ? A file manipulation command that extracts some of the records from a file is called SELECT

Create a entity-relationship diagrams, This project requires you to create ...

This project requires you to create a database design.  Your design will be documented in a set of Entity-Relationship diagrams.  Draw a set of Entity-Relationship diagrams to mode

Describe the algorithm for updating indices, Describe the algorithm for upd...

Describe the algorithm for updating indices for a single level index when a record is    (i) Inserted  (ii)  deleted What will be the modification if there are multilevel in

What is meant by the degree of relationship set, What is meant by the degre...

What is meant by the degree of relationship set? The degree of relationship type is the number of participating entity types.

Relational schema, crete a data base relationship model Entity: ...

crete a data base relationship model Entity: Students; Professors; Dormitories buildings; Attributes of students: Name; Address; Dorm;

State in detail about data flow diagram, What is a Data Flow Diagram?  ...

What is a Data Flow Diagram?  Data Flow Diagram: A data flow diagram is the graph that shows flow of data values from their sources in objects in the course of processes whic

Explain the relational completeness, Explain the Relational Completeness ...

Explain the Relational Completeness Codd described the term relational completeness to consider to a language that is complete with respect to first-order predicate calculus ex

What is called block-level striping, What is called block-level striping? ...

What is called block-level striping? Block level striping stripes blocks across many disks. It treats the array of disks as a large disk, and provides blocks logical numbers

Which is the properties of entities, Which is the properties of entities? ...

Which is the properties of entities? Attributes is the properties of entities.

What are uncommitted modifications, What are uncommitted modifications? ...

What are uncommitted modifications? The immediate-modification technique permits database modifications to be output to the database whereas the transaction is still in the act

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd