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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
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Q. Explain data aggregatio n and discuss different design constraints. Sol. Aggregation One limitation of the E-R model is that it cannot express relationships amon
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