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Entity types that do not have any key attribute, and therefore cannot be identified independently, are known as weak entity types. A weak entity can be recognized uniquely only by considering some of its attributes in conjunction with the primary key attributes of another entity, which is known as the identifying owner entity.
Usually a partial key is attached to a weak entity type that is used for unique identification of weak entities associated to a particular owner entity type. The following restrictions must hold:
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What is meant by heuristic optimisation?Discuss the major heuristics that are applied during query optimisation.
Define Specialisation and generalization in brief? Specialisation / generalization: Generalization or Specialization represents the is a relationship set, an necessary element
Due date for May 8
#question.what is mapping constraints and types?.
What is the use of integrity constraints? Integrity constraints make sure that changes made to the database by authorized users do not result in a loss of data consistency. The
Synonyms It allows short names or alternative names for objects. Example : CREATE SYNONYM D30 FOR EMPD30; Now if we give command:
Represent the following scenarios with E-R diagrams drawn using the ER Assistant software. The diagrams should indicate cardinality and optionality of relationships. Transform each
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