Developer discussion for Creative Commons technology and tools

[Jon Phillips <jon AT rejon.org>]

On Fri, 2007-07-27 at 22:26 -0700, Jason Kivlighn wrote:
> Hey all,
> 
> I'm currently adding license selection based on
> Permits/Requires/Prohibits flags to liblicense.  At the moment, I'm
> ironing out the API, and would appreciate any feedback.  Here's some
> working sample code, with inline comments explaining the details:


>     char *attributes[] = {
>             "http://creativecommons.org/ns#Distribution";,            //0
>             "http://creativecommons.org/ns#CommercialUse";,        //1
>             "http://creativecommons.org/ns#DerivativeWorks";,    //2
>             "http://creativecommons.org/ns#ShareAlike";,                //3
>             "http://creativecommons.org/ns#Attribution";,            //4
>             NULL
>     };
>     //build a structure for fast searching of licenses on the given
> attributes
>     ll_license_chooser_t *license_chooser =
> ll_new_license_chooser(attributes);
>    
>     int permits_flags, requires_flags, prohibits_flags;
>    
>     //permits Distribution(0) and DerivativeWorks(2)
>     permits_flags = (1 << 0) | (1 << 2);
>    
>     //requires ShareAlike(3)
>     requires_flags = (1 << 3);
>    
>     //doesn't prohibit any particular attribute, but could still
> prohibit an attribute that isn't in the 'attributes' list
>     prohibits_flags = 0;
>    
>     //Attribution(4) and CommercialUse(1) must be unspecified in the
> license RDF.
>     //If you don't want this to be the case, leave these two attributes
> out of the list that is
>     //passed to ll_new_license_chooser()
>    
>     //returns GPL and LGPL
>    
> ll_get_licenses_from_flags(license_chooser,permits_flags,requires_flags,prohibits_flags);
> 
>     //another example:
> 
>     //permits Distribution(0)
>     permits_flags = (1 << 0);
>    
>     //requires ShareAlike(3)
>     requires_flags = (1 << 4);
>    
>     //prohibits CommercialUse(1)
>     prohibits_flags = (1 << 1);
> 
>     //returns all by-nc-nd licenses
>    
> ll_get_licenses_from_flags(license_chooser,permits_flags,requires_flags,prohibits_flags);
> 
> Doing some quick benchmarking, ll_new_license_chooser() takes .730s
> (which includes a call to ll_get_all_licenses()).  After that, calls to
> ll_get_licenses_from_flags() are extremely fast -- it's a constant time
> algorithm (100,000,000 calls ran in less than 7 seconds); this makes it
> highly effective for use in a graphical license chooser where the user
> clicks checkboxs to specify the flags, and the selected license is then
> updated.
> 
> The goal is to provide easily integrated license selection in
> applications.  For example, a user should be able to say, "I want a
> license that allows sharing, derivative works, and commercial use."  A
> simple call to ll_get_licenses_from_flags() with the appropriate flags
> returns what the user wants.
> 
> As-is, this code should include the functionality necessary for the
> nautilus license extension (coming out with Liblicense 0.3) and the KDE4
> equivalent that I'm working on (These function like the mock-ups at
> http://wiki.creativecommons.org/Desktop_Integration).  Are there use
> cases I'm missing?
> 
> Cheers,
> Jason

This sounds good...if we need to add more, we can in the future...man,
that is some massive speedup! The Open Font License, cc-like metadata
has some other attributes, and I'm sure to express others, will need
more attributes, but for our purposes, this sounds wise...excellent!
Commit it!

Jon

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-- 
Jon Phillips

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