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GO Classes DPP | GATE CS, DA | DBMS | Variable-Length Record

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Which of the following are benefits of using a record header for variable-length records?

  1. Delimiter characters between fields are not required.
     
  2. It always uses equal or less space than a fixed-length record representation.
     
  3. An individual field can be accessed without scanning all preceding variable-length fields.
     
  4. It permits a compact representation of NULL values.

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A is true.

One possible variable-record representation is:

$$\mathrm{F1\ \$\ F2\ \$\ F3\ \$\ F4}$$

but then locating a later field requires scanning through delimiters.

We can keep field offsets in the record header, so delimiters are unnecessary.
 

B is false.

A record header itself consumes metadata space. 

Therefore, it is not guaranteed to use less storage than every possible fixed-length representation.
 

C is true.

Suppose the header contains offsets:

$\mathrm{offset(F1)}$

$\mathrm{offset(F2)}$

$\mathrm{offset(F3)}$

$\mathrm{offset(F4)}$

The DBMS can obtain the beginning of $\mathrm{F3}$ directly rather than scanning $\mathrm{F1}$ and $\mathrm{F2}$.
 

D is true.

NULL can be represented through header metadata or a null pointer rather than reserving the full field value space. 

 

 

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