Consider a hash function, h, that takes as an argument a value of a composite search key that is a sequence of r attributes, a 1 , a 2 ,...,a r .If h has the form
h(a1? a2? ...? ar)=h1(a1) ? h2(a2) ? ...? hr(ar)
where hi is a hash of attribute ai and ? is the concatenation operator, h is referred to as a partitioned hash function. Describe the advantages of such a function with respect to equality, partial-key, and range searches.
No advantage with respect to equality searching. For partial key searches we can use the attributes that are provided to get part of the identi?cation of the buckets in which target tuples can reside. All buckets satisfying this partial identi?cation have to be searched since any might contain target tuples. This narrows the search since a hash function that is not partitioned would require that all buckets be searched. The same bene?t applies to range searches, although the range information for a particular attribute cannot be used.
You might also like to view...
When the viewer places the mouse pointer over a link, the pointer's appearance changes to a(n) ____ icon.
A. hourglass B. pointing finger C. stopwatch D. click
The Group Policy settings Prevent Deleting Download History and Prevent users from bypassing SmartScreen Filter's application reputation warnings about files that are not commonly downloaded from the Internet are used to control ________ Manager in IE9 and IE10
Fill in the blank(s) with correct word
The behavior of hyperlinks cannot be modified with Cascading Style Sheets.
Answer the following statement true (T) or false (F)
A synchronous password token has to operate at the same pace as the receiver. That is, the token has to advance to the next random number at the same time the receiver advances. Because of clock imprecision, the two units will not always be perfectly together; for example, the token’s clock might run 1 second per day slower than the receiver’s. Over time, the accumulated difference can be significant. Suggest a means by which the receiver can detect and compensate for clock drift on the part of the token.
What will be an ideal response?