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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
It defines that no primary key value can be null. This is as the primary key is used to recognize individual tuple in the relation. So we will not be able to recognize the records
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