12 - Record Locking and Redundancy

 1. Record locking is the technique of preventing simultaneous access to data in a database, to prevent ____________________

  inconsistent results.

  the over writing of primary keys

  the addition of data to the database

  hacking or a lack of security

 2. In this classic example (see excerpt below), fill in the blanks with the most appropriate statement.
The classic example is demonstrated by two bank clerks attempting to update
 the same bank account for two different transactions. Clerks 1 and 2 both 
retrieve (i.e., copy) the account's record. 

Clerk 1 applies and saves a transaction. 

Clerk 2 applies a different transaction to his saved copy, 
and saves the result, based on the original record and his changes, 
overwriting the transaction entered by clerk 1. 

The record ___________________________________________________________

  will reflect both the first and the second transaction

  no longer reflects the first transaction, as if it had never taken place

  no longer contains any data at all, as it will contain a NULL value

  will no longer reflect the second transaction, as the first record remains locked

 3. A simple way to prevent the over writing of data is to ______________________________ by any user, so that no other user can save data.

  unlock the file whenever a record is being deleted

  lock the file whenever a record is being modified

  unlock the file whenever a record is being modified

  lock the file whenever a record is being added or deleted

 4. Locking a file prevents records from being overwritten incorrectly,and allows only _________________ locking out other users who need to edit records at the same time

  two records to be processed simulatenously

  all records to be deleted simulateously

  one record to be processed at a time

  one record to be deleted after the previous record

 5. To allow ___________________________ and also prevent inconsistencies created by unrestricted access, a single record can be locked when retrieved for editing or updating

  a single user to edit a database at any given time

  no access, even to authorised users

  single user access

   several users to edit a database table at the same time

 6. In database management theory, locking is used to implement ___________ among multiple database users. This is the "I" in the acronym ACID





 7. Fill in the blanks for the following excerpt
_______________is a condition created within a database or 
data storage technology in which the same piece of data is 
held in two separate places.

This can mean two different fields within a single database, 
or two different spots in multiple software environments or 
platforms. Whenever data is repeated, this basically 
constitutes ______________.

  Data validation

  Data integrity

  Data restoration

  Data redundancy

 8. In the following example _________________________.
Marvin 33, Male, Lawyer
Marvin, 33, 3 Riverdale Drive
Marvin, employee number 22345

  there is no evidence of duplication

  the name and the age is duplicated

  there is no evidence of data redundancy

  only the name has been duplicated three times

 9. Data redundancy is usually the mark of an inefficient database and people go to great lengths to avoid it



 10. Data redundancy in a database means that the same data is present in more than one table