Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Explain the concept of generalization and aggregation in E_R diagrams. Give one example for each one of them?
Generalization: Consider extending the entity set account through classifying accounts as being either savings-account or chequing-account. Each of these is described through the attributes of account plus additional attributes. (Savings has interest-rate and cheque has overdraft-amount.) We can express the similarities among the entity sets through generalization. This is the procedure of forming containment relationships among a higher-level entity set and one or more lower-level entity sets.
Aggregation: The E-R model cannot express relationships between relationships. When would we require such a thing?
Consider a DB along with information about employees who work on a particular project and use a number of machines doing in which work. We get the E-R diagram shown in Figure.
Figure: E-R diagram with redundant relationships
Relationship sets work and uses could be combined into a single set. Therefore, they shouldn't be, as this would obscure the logical structure of this scheme. The solution is to use aggregation.• An abstraction by those relationships is treated as higher-level entities.• For our instance, we treat the relationship set work and the entity sets employee and project as a higher-level entity set called work.• Another figure shows the E-R diagram with aggregation.
Relations create the database. They must satisfy various properties, like no duplicate tuples, no ordering of tuples, and atomic attributes, etc. Relations that satisfy these basic
Briefly describe concurrency execution? Lock - based protocols Locks There are several modes in which a data item may be locked in this section we restrict our attention
Automated system for appointment with sms and call confirmation with service providers and user has to be initiate automatically. After selecting time and date to use service, s
Let us now talk about the relational operations: SELECT The select operation is used to select few specific record from the database based on different criteria, This is a un
In Oracle what is system global area and how is it organized? The SGA is a collection of shared memory fields which along with the Oracle processes constitute an Oracle instan
What is Stored Procedure? A stored procedure is a named group of SQL statements that have been previously formed and kept in the server database. Stored procedures accept input
Question 1: a) What is the difference between a non-impact and impact printer? b) Which type of printer is generally used in a supermarket to print your receipt? Describe
The Transactions- A transaction is definite as the unit of work in a database system. Database systems that deal with a huge number of transactions are also termed as transaction p
Question 1: Define the term business intelligence tools? Briefly explain how the data from one end gets transformed into information at the other end? Definition Exp
Define the Division Operation of Relational Algebra Let R be a relation comprising attributes (A1,...Ap,Ap+1,...An) and S comprising attributes (Ap+1,...An) DEF: Division
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!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd