Xapian devel - Dec 2014 - Adding Support for Krovetz Stemmer Algo in Xapian

Hello,

As mentioned on the project ideas page, Adding more support for stemmer
algorithm,

 i found an implementation of Krovetz Stemmer Algo in C++ but before
working on it to merge it into xapian, i needed help in recognizing the
license information associated with the source code.

To avoid further licensing issues kindly someone check the link

http://sourceforge.net/p/lemur/wiki/KrovetzStemmer/

-Abhishek
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On 29 Nov 2014, at 15:34, Abhishek Singh Kushwah <abhishek18kushwah at
gmail.com> wrote:
> As mentioned on the project ideas page, Adding more support for stemmer
algorithm,
> 
> i found an implementation of Krovetz Stemmer Algo in C++ but before working
on it to merge it into xapian, i needed help in recognizing the license
information associated with the source code.
> 
> To avoid further licensing issues kindly someone check the link 
> 
> http://sourceforge.net/p/lemur/wiki/KrovetzStemmer/  
The project suggests it?s under a BSD license, but the code itself is a mire of
confusion, citing that license (by URL), and an ?all rights reserved? copyright
statement underneath. Since the BSD license grant is for ?use of the Lemur
Toolkit?? I don?t think we can reasonably assume that the individual code is
actually licensed appropriately for us to use.

Our general attitude, based on past experiences with ?foreign? code, is that
unless you?ve written it, it?s difficult for us to accept it.

Best,
James

-- 
 James Aylett, occasional trouble-maker
 xapian.org

[Please keep replies on the mailing list so that everyone can help and benefit.]

On 30 Nov 2014, at 17:51, Abhishek Singh Kushwah <abhishek18kushwah at
gmail.com> wrote:
> Two of the implementation of algorithms has already been rejected
previously due to licenses both being the implementation of porter but our
xapian use implementation in snowball which i assume is under GPL.
Snowball (and the stemmer implementations shipped with it) is under a BSD
license.
> Tell me how can a stemmer algo possible so lengthy be incorporated in a
bit-size project if we have to code it from the scratch.
Krovetz isn?t actually particularly lengthy for a hand-coded algorithm; it?s
about 1000 lines (and then almost another 6000 lines of dictionaries). I think
the problem here is that Krovetz doesn?t seem amenable to implementing directly
in Snowball, which means more work. The original paper
<http://people.scs.carleton.ca/~armyunis/projects/KAPI/Krovetz.pdf>
doesn?t describe the algorithm particularly concisely, but it doesn?t seem
hugely difficult or time-consuming to implement, although there are always
concerns about efficiency in stemming algorithms.

We?d need a dictionary or dictionaries from somewhere; I?m not clear from a
quick skim of the paper what we?d need to do to construct useful ones. Also note
from
<http://www.comp.lancs.ac.uk/computing/research/stemming/general/krovetz.htm>
that Krovetz, in IR, is often combined with other stemmers; at the moment we
don?t provide a way of ?chaining? stemmers together. (This could separately be a
bite-sized project, however, as it doesn?t sound terribly complex.)

If you can get an explicit license grant from the copyright holder of the
Krovetz stemmer (which seems to be either the University of Massachusetts or the
Applied Computer Systems Institute of Massachusetts, Inc. ? it?s unclear from
the Krovetz source code), then (providing it?s compatible) we could accept a
derived version directly into Xapian. The problem is the ambiguity about
licensing, which is made worse by pointing to
<http://www.lemurproject.org/license.html> which asserts yet another
copyright holder (albeit also asserting BSD, so if the other two claims are
taken care of cleanly then it?ll work out).

J

-- 
 James Aylett, occasional trouble-maker
 xapian.org

On Sun, Nov 30, 2014 at 03:28:35PM +0000, James Aylett
wrote:
> On 29 Nov 2014, at 15:34, Abhishek Singh Kushwah <abhishek18kushwah at
gmail.com> wrote:
> > i found an implementation of Krovetz Stemmer Algo in C++ but before
> > working on it to merge it into xapian, i needed help in recognizing
> > the license information associated with the source code.
> > 
> > To avoid further licensing issues kindly someone check the link 
> > 
> > http://sourceforge.net/p/lemur/wiki/KrovetzStemmer/  
> 
> The project suggests it?s under a BSD license, but the code itself is
> a mire of confusion, citing that license (by URL), and an ?all rights
> reserved? copyright statement underneath. Since the BSD license grant
> is for ?use of the Lemur Toolkit?? I don?t think we can reasonably
> assume that the individual code is actually licensed appropriately for
> us to use.
I think a bigger issue is that this licence is actually a variant of the
BSD licence which is probably GPL-incompatible.

Here's the two licences to compare:

http://www.lemurproject.org/license.html
http://directory.fsf.org/wiki/License:BSD_3Clause

Clauses 1 and 2 are the same, the capitalised disclaiming
of warranties is the same except for "AUTHOR" being substituted, and 3
is similar but with "author" substituted and some rewording.

But the added clause 4 is problematic as it renders the licence
incompatible with the GPL.  It's essentially the same as clause 4
of the PHP licence:

http://php.net/license/3_01.txt

And that clause apparently is a strong restriction on naming derived
products:

http://www.gnu.org/licenses/license-list.html#PHP-3.01

Cheers,
    Olly

> On 30 Nov 2014, at 17:51, Abhishek Singh Kushwah <abhishek18kushwah at
gmail.com> wrote:
> 
> > Two of the implementation of algorithms has already been rejected
> > previously due to licenses both being the implementation of porter
> > but our xapian use implementation in snowball which i assume is
> > under GPL.
The only cases I can think you might be referring to are two different
submissions of patches based on Andy Stark's implementation of the
Paice/Husk stemmer (not the Porter stemmer).  The problem there is that
this implementation has no explicit licence, which means we simply can't
use it:

http://www.gnu.org/licenses/license-list.html#NoLicense

Cheers,
    Olly