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A super key is an attribute or set of attributes used to recognize the records uniquely in a relation.
For instance, in the Relation PERSON defines earlier PERSON_ID is a super key since PERSON_ID is unique for every person. Likewise (PERSON_ID, AGE) and (PERSON_ID, NAME) are also super keys of the relation PERSON as their combination is also unique for each record.
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
The Maximum no of key fields that can be used in a header is?? 50
Describe log based recovery The most usably structure for recording data base modification is the LOG the log is a sequence of log records recording all the update activities i
Example : Create a sequence named SEQSS that starts at 105, has a step of 1 and can take maximum value as 2000. CREATE SEQUENCE SEQSS START WITH 105 INCREMENT BY 1 MAX VA
Examples:- Hierarchical Model: It tells data as and relationships by hierarchy of data values. Figure illustrates an example of hierarchical model. Now a day's these models are
Explain Foreign Key? Foreign Key - Let there are two relations (tables) R and S. Any candidate key of the relation R that is referred within the relation S is known as the fo
Question : (a) Differentiate between database integrity and database security (b) Database security involves measures to avoid loss of privacy and loss of confidentiality. D
List any two disadvantages of a database system ? The disadvantages of database system are: • Database systems are difficult, complex, and time-consuming to design. • Substanti
Explain the function of input controls. Identify four types of input control and explain the function of each. Provide an example of a data integrity error that could occur i
How does a query tree represent a relational algebra expression? Discuss any three rules for query optimisation, giving example as to when should each rule be applied. Ans
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