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What is magnetic disks?explain it?
Magnetic disk provides the bulk of secondary storage of modern computer system. The disk capacity is growing at over 50% per year. But the storage needs of large applications have also been growing very fast and in some case each faster than the growth rate of disk capacities. A large data base may need 100 of disks.
Physical characteristics of disk
Physical disks are relatively simple. Every disc platter has a flat circular shape
We can call magnetic disk as
Ø hard disk
Ø Floppy disk
The read write head keeps information on a sector magnetically as reversals of the direction of magnetization of the magnetic material. There might be hundreds of concentric tracks on a disc surface, having thousands of sectors.
Representing complex relationship among data A database may contain varieties of data interrelated to each other in numerous ways. A DBMS must have the capability to represent
Which operator is used to compare a value to a list of literals values that have been specified? BETWEEN operator is used to compare a value to a list of literals values that h
Partial Key : It is a group of attributes that can uniquely identify small entities and that are related to same base entity. It is sometime named as Discriminator. Altern
Explain Recursive relationship type? Recursive relationship type: A recursive relationship is one in that the similar entity participates more than once in the relationship
What is a disjoint less constraint? Ans: It needs that an entity belongs to no much more than one level entity set. Disjoint less constraint needs that an entity belongs to
What is a heterogeneous distributed database? In a heterogeneous distributed database, dissimilar sites may use different schemas, and dissimilar dbms s/w. The sites may not be
explain the mapping constraints
Surgeons identified by doctor ID (DOCID) operate on patients identified by patient ID (PATID) in operating theaters identified by room numbers (ROOMNO). Each surgeon can operate on
Write short note on Data models? Data models: A data model is an abstract model which elaborates how data is represented and accessed. The term data model has two commonly ac
What is Primary key? Primary Key - Primary key is one of the candidate keys which uniquely identifies each row in the relation.
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