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> From: [EMAIL PROTECTED]> To: pgsql-hackers@postgresql.org> Tasneem,> > > > > 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.> > Are we talking about a mathematical calculation on the > values, or an algorithm > against the population of the result set? I'm > presuming the latter or you > could just use a function. If so, is NEAR an > absolute range or based on > something logarithmic like standard deviation?> It is based on fuzzy logic.. we take the operand2 (which is a crisp value, given by the end user) as a fuzzy set.. assign membership degree to its elements.. and then get the values between 1.0 to 0.8 as the values NEAR to the operand2, and output those as the result. I have made the initial membership degree constant, i.e 0.8. But that doesn’t mean that the size of the set defined by NEAR (md=0.8) remains constant. The larger the operand2 set, the larger the range of the set defined by NEAR. > Beyond that, I would think that this mechanism would need some kind of extra > > heuristics to be at all performant, otherwise you're querying the entire > > table (or at least the entire index) every time you run a query. Have you > > given any thought to this?> Yes u are right.. that’s my main concern. Here I have just put forward an idea to incorporate fuzziness in current database systems through the ANSI SQL; but still I have to look into that problem if it is to be functional at all with large amount of data. Tasneem Memon _________________________________________________________________ Connect to the next generation of MSN Messenger http://imagine-msn.com/messenger/launch80/default.aspx?locale=en-us&source=wlmailtagline
