Er schema can be represented by relation schemas , Database Management System

Q. Describe how an ER schema can be represented by relation schemas and constraints arising from ER design can be mapped to constraints on a relation schema.   

The entity relationship data model is based on a perception of a real world that consists of basic objects called entities and of relationships among these objects. An entity is thing or object in the real world that is distinguishable from other objects. For eg., each person is an entity and band accounts can be considered as entities. Entities are described in a database by set of attributes. For eg., the attributes account number and balance may describe one particular acconunt in a bank and they form attributes of the account entity set. An extra attribute customer id is used to uniquely identify customers. A relationship is an association among several entities. For eg., a depositor relationship associates a customer with each account that he has. The set of all entities of the same type and the set of all relationship of the same type are called entity set and relationship set respectively. The overall logical structure of a database can be expressed graphically by and ER diagram, which is buily up using : R ectangles -  which represent entity sets    Ellipses -  which represent attributes     Diamonds -  which represent relationships   Lines -  which represent link attributes to entity sets.   Each component is labelled with the entity or relationship that it represents.  Constraints to which the contents of database must confirm. For eg.,  mapping cardinalities, which express the number of entities to which another entity can be asociated via a relationship set.                                                                                                                  

Posted Date: 7/11/2012 4:07:29 AM | Location : United States







Related Discussions:- Er schema can be represented by relation schemas , Assignment Help, Ask Question on Er schema can be represented by relation schemas , Get Answer, Expert's Help, Er schema can be represented by relation schemas Discussions

Write discussion on Er schema can be represented by relation schemas
Your posts are moderated
Related Questions
What is meant by heuristic optimisation?Discuss the major heuristics that are applied during query optimisation.

Un-Normalized Form (UNF) If a table having non-atomic values at every row, it is said to be in UNF. An atomic value is something that cannot be further decomposed. A non-atomic

Multiple-mode locks : It offers two locks: exclusive locks and shared locks. But why do we require these two locks? There are a lot of transactions in the database system that neve

Define Specialisation and generalization in brief? Specialisation / generalization: Generalization or Specialization represents the is a relationship set, an necessary element

The First Normal Form (1NF) Let us first describe 1NF: Definition: A relation (table) is in 1NF if 1.      There are no duplicate tuples or rows in the relation. 2.

What is relationship instance ? Relationship Instance - A relationship is a relation between two or more entities. An instance of relationship set is a set of relationships.


Mention the purpose of SID and SOD lines SID (Serial input data line): It is an input line by which the microprocessor accepts serial data. SOD (Serial output data line)

Write short notes on relational model   The  relational  model  uses a  collection of  tables  to show  both data  and the relationships between those  data.  The relational mo

Discuss the problem of Spurious tuples and how we may prevent it.    Ans:  A spurious tuple is, mainly, a record in a database that gets created while two tables are joined bad