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

Assignment Help:

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.                                                                                                                  


Related Discussions:- Er schema can be represented by relation schemas

Hierarchical data representation model, Examples:- Hierarchical Model: I...

Examples:- Hierarchical Model: It tells data as and relationships by hierarchy of data values. Figure illustrates an example of hierarchical model. Now a day's these models are

Generalization and specialization, design a generalization specialization h...

design a generalization specialization hierarchy for a motor vehicle sales company. the company sells motorcycles, passenger cars, vens and buses.

Management information system, management information system based on funct...

management information system based on functional organisation

Query processor in database management system, Query Processor The qu...

Query Processor The query language processor is responsible for taking query language statements or shifting them from the English-like syntax of the query language to a form

Explain the two constraints check and foreign key in sql, Explain the two c...

Explain the two constraints, check and foreign key in SQL along with an example for each. Give the syntax. CHECK constraint - CHECK constraint specifies an expression which

Write a short note on built in function in qbe, Write a short note on built...

Write a short note on built in function in QBE? Built in function in QBE: QBE involves various built in functions like AVG, MAX,MIN,SUM and CNT. We must prefix these operator

Create a company database, Company Database: a-)Here is the ER Model ...

Company Database: a-)Here is the ER Model b-)Here is the Relational Model:     IMPORTANT NOTICE FOR SOLUTION TYPE: ***THIS ASSIGNMENT WILL BE SOLVED BY THE

What is a records management consultation, What is a records management con...

What is a records management consultation? Our organization is an authority for disseminating your specific requirements and giving you with a solution to effectively manage yo

Explain network model in dbms, Explain Network Model in DBMS? Network ...

Explain Network Model in DBMS? Network Model - It was formalised within the late year of 1960s through the Database Task Group of the Conference on Data System Language (DBTG

Evaluate the null hypothesis, 1.Suppose you are given a dataset that consis...

1.Suppose you are given a dataset that consists of a random sample of tasters, on which the following variables were obtained: (y) Zpref = taste preference for green beans store

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