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Aggregation
Aggregation is stronger form of association. It represents the "has-a" or "part-of" relationship. An aggregation association depicts a complex object which is composed of other objects. You can characterize a house as a combination of its roof, floors, walls, foundation, windows, and rooms and so on. A room may in turn be, composed of walls, floor, ceiling, doors and windows, as shown in Figure.
In UML, a link is placed among the "whole" and "parts" classes, with a diamond head (Figure) attached to the complete class to indicate which association is an aggregation. Multiplicity can be precise at the end of the association for each of "part-of" classes to indicate constituent parts. The method of decomposing a complex object into its component objects can be extended until desired level of detail is reached.
Figure: A house and some of its component
Define lock? Lock is the most common used to execute the requirement is to permit a transaction to access a data item only if it is currently holding a lock on that item.
A constraint named less_than_20 was defined on the field date_of_birth of table student. Delete this constraint. ALTER TABLE student DROP CONSTRAINT less_than_20;
What is persistency? Persistency ensures which data is stored and that after the object is no longer available (program stops running) the data will be available to other users
. Ashutosh Dubey who is the director of Gyan Gurukul want a three-level schema architecture for the Gyan Gurukul Company that provide better security also design a data abstraction
Create role named role_table that allows a user to create tables. Using role_table allow users kripa and reena to create tables. CREATE ROLE role_table; GRANT CREATE ANY TABLE
in case of functional dependencies how we get the higher normal form.
Saving Derived Attributes to Avoid Re-computation Data that is derived from other data should be stored in the computed form to avoid re-computation. For this, we could define
What is Cardinality Ratio? Cardinality Ratios - The cardinality ratios for relationship kinds specifies the maximum number of relationship instances in which an entity can pa
sy bcs project of hospital managment system
what would go in order patient#, patient name, patien address, surgeon#, surgeon name, surgery date, surgery type, drug admin
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