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.
(a) Provide the description of the following ODMG schema in the Object Definition Language (ODL). (b) Based on the above object database, write the following queries i
Explain the EXISTS and UNIQUE functions of SQL. Give an example for each? EXISTS: The EXISTS function takes one parameter that is a SQL statement. If any records exist which
This assignment concerns the Research database. The database ER model is shown above, where attributes are omitted for clarity. The relational model for the database is: Departm
What are multiple inheritances? Multiple inheritances allow a class to inherit variables and methods from many super classes.
What is Asterisk in SQL? Asterisk (*): In SQL, the columns for all the tables and views in the FROM clause will be displayed.
How external/conceptual mapping and conceptual /internal mapping is performed
Normal 0 false false false EN-US X-NONE X-NONE
read-set(T) : Each data items that are read by a transaction T Timestamps : for all transaction T, the start-time and the end time are reserved for all the three phases.
Project Description: Looking to prepare automated trading engine for alternate cyprto currencies starting with Cryptsy, finally integrating into other exchanges. Need to work wi
Why a report generator is used ? Report generator is used for print files on paper.
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