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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 accepted meanings:
• A data model theory that is a formal description of how data may be structured and accessed.• A data model instance that is applying a data model theory to create a practical data model instance for a few particular application.
Define canonical cover? A canonical cover Fc for F is a set of dependencies like F logically implies all dependencies in FC and Fc logically shows all dependencies in F.
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 st
aggregation
What is System R? What are its two major subsystems? System R was intended and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its pur
Objectives After reading this unit you should be able to: Explain storage of databases on hard disks; Discuss the execution of various file Organisation techniques;
What are the DBMS languages? Briefly explain? Data Definition language (DDL):A database schema is specified through a set of definitions expressed through a special language
Lack of Redundancy We have talked about the problems of repetition of information in a database. Such repetition should be stay away as much as possible. Let us state once again t
How to create a table from existing table? Create table as e.g, To create a new table ‘N_emp' with employee names and their identification numbers only from employee ta
What are the two integrity rules? Ans: The two integrity rules are: Entity Integrity Rule & Referential Integrity Rule. Entity Integrity Rule - If the attribute A of rel
Which is a valid SQL type? A valid SQL Should be in CHARACTER it is should be NUMERIC and FLOAT.
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