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What is serializability? Explain its types?
The data base system must control concurrent implementation of transactions, to ensure that the data base state remains consistent. There are dissimilar forms of schedule equivalence they lead to the notions of
a) Conflict serializability
B) View serializability
Conflict serializability
We say that ii and I j conflict if they are operations by dissimilar transaction on the similar data item and at least one of these instruction is a write operations
Describe the Composite Key Composite Key: Sometimes one key is not enough to uniquely recognize a row. E.g. in a single class Roll is enough to search a student, but in the w
Consider the subsequent relations for a database which keeps track of business trips of salespersons in a sales office: SALESPERSON (SSN, Name, start_year, Dept_no) TRIP (SSN, Fr
What is the disadvantage of a call by reference? During a call by reference damage or loss of data is not restricted to the subroutine, but will instantly lead to alters to th
What is meant by functional dependencies? Consider a relation schema R and α C R and β C R. The functional dependency α ->β holds on relational schema R if in any legal relati
Relational and E-R Model There are three types of constraints on relational database that have: DOMAIN CONSTRAINT PRIMARY KEY CONSTRAINT INTEGRITY CONSTRAINT
Describe Object Relational model ? Object Relational Model - This model combines the characteristics of both relational model and object oriented model. It extends the tradit
In an E-R diagram how attributes are represented ? In an E-R diagram attributes are represented in a ellipse.
Define a relation ? Relation - A relations is a named two-dimensional table of data. Mathematically, a relation can be described as a subset of the cartesian product of a lis
Explain the term- Query. Queries are used to repossess and show specific records in a table. They can also be used to show specific fields of specific records, which meet the co
Consider the relations EMP(ENO,ENAME,AGE,BASIC_SALARY) WORK_IN(ENO,DNO) DEPT(DNO,DNAME,CITY) Express the following queries in SQL (i) Find names of employees who work in a dep
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