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

ER Diagram, Hi I have got an assignment for making an er diagram for market...

Hi I have got an assignment for making an er diagram for market management software can any budy help me?

What is the use of raid, What is the use of RAID? A variety of disk-org...

What is the use of RAID? A variety of disk-organization methods, collectively called redundant arrays of independent disks are used to better the performance and reliability.

Discuss the problem of spurious tuples, Discuss the problem of Spurious tup...

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

I need help on the following 5 questions, 1. Define and discuss Work Breakd...

1. Define and discuss Work Breakdown Structure, Critical Path Analysis, PERT charts and GANTT charts. Describe the role of each in determining scope, budgets, and schedules? What

DBMS, give some example real life situation where DBMS are most suitable

give some example real life situation where DBMS are most suitable

Design and building a distributed information system, prototype of a distri...

prototype of a distributed information system for a national car part retail outlet chain.

What are the disadvantages of relational data, What are the disadvantages o...

What are the disadvantages of relational data ? Disadvantages • Performance - If the number of tables among that relationships to be established are large and the tables t

Explain concurrency problems, Question: a) There are three concurrency...

Question: a) There are three concurrency problems, i.e. three types of potential mistake which could occur if concurrency control is not properly enforced in the database syst

Sorting-stacks, 1. Identify the comparisons and exchanges made to sort the ...

1. Identify the comparisons and exchanges made to sort the following array using the selection exchange sort technique. Note: you may not need all columns. Ori

Benefits and drawbacks of sequential file organisation, Benefits of Sequent...

Benefits of Sequential File Organisation It is quick and efficient when dealing with huge volumes of data that require being processed periodically (batch system). Dra

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