Database-MySQL [3i Infotech Placement]: Sample Questions 92 - 93 of 162
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Question 92
Explanation
- An entity set is a set of entities of the same type (e. g. , all persons having an account at a bank) .
- Entity sets need not be disjoint.
- For example, the entity set employee (all employees of a bank) and the entity set customer (all customers of the bank) may have members in common.
Five entity sets in this section:
- Branch: The set of all branches of a particular bank.
- Each branch is described by the attributes branch-name, branch-city and assets.
- Customer: The set of all people having an account at the bank.
- Attributes are customer-name, S. I. N. , street and customer-city.
- Employee: With attributes employee-name and phone-number.
- Account: The set of all accounts created and maintained in the bank.
- Attributes are account-number and balance.
- Transaction: The set of all account transactions executed in the bank.
- Attributes are transaction-number, date and amount.
Question 93
Explanation
- Responsible primarily for managing the operations inherent saving and loading of the blocks.
- Reads disk pages into a main memory page as needed.
- Used by access methods, heap files, and relational operators to read/write page.
- Makes calls to the underlying DB class object, which actually performs these functions on disk pages.
- Must use some techniques in order to provide good service:
- Replacement Strategy
- Pinned Blocks
- Forced Output of Blocks