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Use Delegation to Share Implementation
The delegation "Delegation comprises of catching an operation on one object and sending it to other object which is part, or related to first object. In this method, only meaningful operations are delegated to second object, and meaningless operations can be banned from being inherited accidentally".
It is actuality that inheritance is an event for implementing generalization, in which behaviour of super class is shared by all of its subclasses. But, sharing of behaviour is justifiable only when a true generalization relationship come across, that is, only when it can be said which subclass is a form of the super class.
What is Management System? A management system is a set of rules and process which help us to create organize and manipulate the database. It also helps us to add, change delet
What is a SELECT operation? The select operation selects tuples that please a given predicate. We use the lowercase letter σ to denote selection.
What is candidate key? Candidate Key - A candidate key of an entity set is a minimal superkey, which uniquely identifies each row in the relation.
Why is database redesign necessary? Database redesign is essential for two reasons. First, redesign is essential both to fix mistakes made during the initial database design. S
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Wait-die" scheme : The idea is based on non-preventive method. It is based on a simple rule: If Ti requests a database resource that is held by T
Every simple attribute of an entity type have a possible set of values that can be attached to it. This is known as the domain of an attribute. An attribute cannot have a value out
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.
To do the division operation R1 ÷ R2, R2 should be a correct subset of R1. In the following example R1 have attributes A and B and R2 have only attribute B so R2 is a correct subse
Give the forms of triggers? The triggering event can be insert or delete. For updated the trigger can state columns. The referencing old row as clause The referencing
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