Explain generalization and aggregation in e_r diagram, Database Management System

Assignment Help:

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.

620_Employee data.png

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.

75_employee data2.png


Related Discussions:- Explain generalization and aggregation in e_r diagram

Database management issues, You are required to write a report which evalua...

You are required to write a report which evaluates two of the following issues in relation to your case study database: a. Security issues b. Performance issues c. Backup

Database tables design and test queries, Load sample data into the database...

Load sample data into the database tables design and test queries to return the following information • All rows and columns for employees • All rows and columns for customers •

Explain current page table and shadow page table, Explain current page tabl...

Explain current page table and shadow page table. The key idea behind the shadow paging method is to maintain two page tables during the life of the transaction: the current pa

What do you understand by data ware house, Question 1: Define the term ...

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

Heuristics, Benefits of using heuristics

Benefits of using heuristics

Answer, what is database management system? & why it is required?

what is database management system? & why it is required?

Illustrate the view of software architecture, Illustrate the view of softwa...

Illustrate the view of software architecture A model is a semantically closed abstraction of system composes of elements. It can be visualized using any of the following five v

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