Dear All,
I am explaining here how i have defined the operators NEAR and NOT NEAR in my
research paper. I want critics/comments from all of you on the operators.
These operators belong to the category of “Fuzzy Operators” proposed in the
paper for ANSI SQL.
NEAR
It deals with the NUMBER and DATE datatypes simulating the human behavior and
processing the information contained in NEAR in the same way as we humans take
it. This is a binary operator with the syntax:
op1 NEAR op2
Here, the op1 refers to an attribute, whereas op2 is a fixed value, both of the
same datatype.
Suppose we want a list of all the VGAs, price of which should be somewhere
around 30$ .. the query will look like:
SELECT *
FROM accessories
WHERE prod_name = ‘VGA’
AND prod_price NEAR 30
A query for the datatype DATE will look like:
SELECT *
FROM sales
WHERE item = ’printer’
AND s_date NEAR 10-7-06
The algorithm for the NEAR operator works as follows:
The margins to the op2, i.e. m1 and m2, are added dynamically on both the
sides, considering the value it contains. To keep this margin big is important
for a certain reason discussed later.
The NEAR operator is supposed to obtain the values near to the op2, thus the
target membership degree(md) is initially set to 0.8.
The algorithm compares the op1(column) values row by row to the elements of the
set that NEAR defined, i.e. the values from md 1.0 to 0.8, adding matching
tuples to the result set.
4. It is very much possible that the result set is empty since no values
within the range exist in the column. Thus, the algorithm checks for empty
result set, and in that case, decreases the target md by 0.2 and jumps to step
3. This is the reason big margins to the op2 are added.
5. In case there are no values in op1 that are between m1 and m2 (where
the membership degree of the values with respect to NEAR becomes 0.1) and the
result set is empty, the algorithm fetches the two nearest values (tuples) to
op2, one smaller and one larger than the op2, as the result.
The algorithm will give an empty result only if the table referred to in the
query is empty.
2. NOT NEAR
This operator is also a binary operator, dealing with the datatype
NUMBER and DATE. It has the syntax:
op1 NOT NEAR op2
The op1 refers to an attribute, whereas op2 is a fixed value, both of the same
data type.
A query containing the operator looks like:
SELECT id, name, age, history
FROM casualties
WHERE cause = ‘heart attack’
AND age NOT NEAR 55
Or suppose we need a list of some event that is not clashing with some
commitment of ours:
SELECT *
FROM events
WHERE e_name= ‘concert’
AND date NOT NEAR 8/28/2007
The algorithm for NOT NEAR works like this:
First of all it adds the margins to the op2, i.e. m1 and m2, dynamically on
both the sides, considering the value op2 contains.
op1 values outside the scope of the op2 (m1, m2) are retrieved and added to the
result.
If the result set is empty, the farthest values within the op2 fuzzy set (those
possessing the least membership degree) are retrieved. This is done by
continuing the search from values with md=0.1 till the md=0.6, where the md for
NOT NEAR reaches 0.4.
Regards,
Tasneem Ishaque Memon MS (Computer Science) Institute of Mathmetics and
Computer Science University of Sindh, Jamshoro Pakistan
http://www.geocities.com/tasneememon/- The process of gaining knowledge is not
producing results but clearing away ignorance.
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