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What are the various symbols used to draw an E-R diagram? Explain with the help of an example how weak entity sets are represented in an E-R diagram.
Various symbols used to draw an E-R diagram
Weak Entity Sets - An entity set that does not have a key attribute is called weak entity set. A weak entity must participate in an identifying relationship type with an owner or identifying entity type Entities are identified by the combination of:• A partial key of the weak entity type• The primary key of the identifying entity type
Example:Suppose that a DEPENDENT entity is identified by the dependent's first name and birhtdate, and the specific EMPLOYEE that the dependent is related to. DEPENDENT is a weak entity type with EMPLOYEE as its identifying entity type via the identifying relationship type DEPENDENT_OF
These are designed to reduce the effects of a database failure and make sure a database is restored to a consistent state if a failure does arise. Manual backup/restore utilities n
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Explain retrieval in QBE? Retrieval in QBE : A "GUI" for expressing queries. Based on the Domain Relational Calculus (DRC) Actually invented before GUIs. Very co
There are three main sources of utilities and applications for a DBMS: a. Vendor applications and utilities are given for working with or maintaining the database, and generally
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Problem: (a) Briefly explain the ‘Hierarchical Database Model' using appropriate diagram. (b) List and briefly describe five potential benefits of the database approach comp
A Functional dependency is described by X Y between two groups of attributes Y and X that are subsets of R specifies a constraint on the possible tuple that can make a relation
What is a relationship called when it is maintained between two entities? A relationship is called Binary relationship when it is maintained between two entities.
The dataset " CFOLYMPICS.XLS " contains the observations used in the above article. The definitions of the variables are also included in this spreadsheet. However, for the purpo
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