[odc-discuss] ODbL: Does publishing Produced Work from Derivative Database trigger Derivative Database ShareAlike?

[Simon Ward]

On Wed, Mar 04, 2009 at 08:03:44PM +0000, Richard Fairhurst wrote:
> Matt Amos wrote:
> 
> > then i must […] provide […] a "diff" between the original database
> > and my Derivative Database. […]

> I think this is an issue with the formats that are admissible for a  
> diff, not with the Produced Work question.

To further add to this:  The ODbL talks about a file of differences, and
doesn’t specify the format.  When we think about a “diff”, we think about
a file that describe each and every addition and removal between one
version of something and another, like the output of the command of the
same name.  This boils down to being a set of instructions for
transforming the input to the output.

> My submission (and that of a few others) to the co-ment page is that  
> osm2pgsql, or indeed any other open source program on a widely used  
> platform, should be acceptable as a diff

Yes, and this program is just the same as a diff:  A set of instructions
for transforming the input to the output.

As a very simple and contrived example, say I have an ASCII text file
and want to encode it with rot-13.  I could have a “diff” of each and
every change:

    < The quick brown fox jumped
    < over the lazy dog.
    ---
    > Gur dhvpx oebja sbk whzcrq
    > bire gur ynml qbt.

Or I could just write a much simpler program that would perform the same
transformation:

    #!/bin/sh
    tr 'a-zA-Z' 'n-za-mN-ZA-M'

I think this is reasonable.  The transformation should be described
fully.  I can’t just say “I used ‘tr’” in my example, that is not
enough.  Saying I used ‘osm2pgsql’ to transform OSM data is similarly
not enough.  I would also have to include the command line options I
used to select projection, for example.

Simon
-- 
A complex system that works is invariably found to have evolved from a
simple system that works.—John Gall
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