Dear John: Thanks for your answers very much. I have found that there were so may technique points in your implementations :). Currently, I am still using my own implementations, and I will let you know if I use your Fastbit code in my research. Thanks again.
Regards, Mian > Dear Mian, > > The bitvector class performs bitwise logical operations as much as > possible in compressed mode, however, there are cases where producing > a uncompressed result is faster, then we produce uncompressed results. > Our VLDB 2004 paper deals with this kind of choices in detail > <http://lbl.gov/%7Ekwu/ps/LBNL-54673.html>. There are additional > details on this issue at <http://lbl.gov/%7Ekwu/ps/LBNL-49627.html> > and <http://lbl.gov/%7Ekwu/ps/PUB-3161.html>. > > There are a number of functions in ibis::index class to sum (OR) a > number of bitmaps together, e.g., sumBits and addBits. These > functions are based on the discussion from VLDB 2004 paper. You might > consider using them instead of your own. > > Now that we are on the issue of whether you can use part of the code > without the rest, I see two related issues. On the patent right, as > long as what you are doing is for research purpose only, you will be > permitted to use the WAH compression implemented in ibis::bitvector > class (under the fair use exception). On the software side, you are > technically still using FastBit code, therefore, must respect FastBit > license (LGPL). By the way, I am not a lawyer and am not authorized > to speak on behalf of my employer (who holds the patent right and owns > the software) on this matter, therefore my answer is purely a personal > opinion. > > John > > > On 10/16/2009 2:41 AM, Mian Lu wrote: >> Hi John: >> >> I am studying your fastbit code recently. I have tried the AND >> operations >> on two bitvector classes, but found that the direct result vector looks >> like not compressed (I observed the output result through the print >> function). Only after the function compress() is executed, then it is >> compressed. Am I right? I want to ask whether this way is more efficient >> than the direct compressed result is produced? Moreover, if I want to >> perform multiple AND on multiple bitvector classes, then the compress() >> should be called after each operation? >> >> Since I also have tried to implement the WAH algorithm by myself, but >> not >> so efficient compared with your fastbit. Therefore I want to adopt some >> codes from your fastbit in my research project (I hope it is okay). >> Thanks. >> >> Regards, >> Mian >> > _______________________________________________ FastBit-users mailing list [email protected] https://hpcrdm.lbl.gov/cgi-bin/mailman/listinfo/fastbit-users
