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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.
Explain what is DDL? DDL - Data Definition Language: statements used to define the database structure or schema. Some examples: CREATE - to create objects in the database ALT
What is trigger Triggers are statements that are implemented automatically by the system as the side effect of a change to the database.
case study
Define Atom of domain relational calculus An atom has the outline 1 , x 2 , ... , x n > -> r , in which r stands for a relation on n attributes and x 1 , x 2 , ... , x n ar
Write an sql statement to find what is the percentage of home policies which are from the state of Arizona out of all Home policies by Policy Value.
Explain the EXEC statement in SQL Ans: All statements which start with EXEC SQL are embedded SQL database statements. High level languages such as C can be employed to write a
Q. Why would you choose a database system instead of simply storing data in operating system file? Define at a base concept in details. Sol. Advantages of Database over Fil
Limitations of File Based System The file-based system has some limitations. The limitations are listed as follows: Isolation and separation of data: When the data is
Timestamps For Read operations: If TS (T) If TS (T) >= W-timestamp (Q), then the transaction T is trying to read a value of data item Q which has been written and committed
Types of data independence Data independence can be classified into the following two types: Physical Data Independence: This means that for any change made in the physi
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