[redland] Re: Perl RDF parser

[Dave Beckett]

>>>Jonas Liljegren said:
> I looked for it in the methods that took URIs, like the perl and C
> dokumentation for parse_as_stream().

So my documentation needs updating!  The perl stuff is pretty
comprehensive in POD format.

> But I don't think that the program should seg-fault. It is Perl.  It
> should only die with a appropriate message.  I must be able to catch
> it (with eval{}).

As I said, the URI handling inside Redland is incomplete.  I'll
record this in the todo list to fix.

> 
> Looking at this page:
>         http://www.redland.opensource.ac.uk/docs/api/r2949.html
> 
> That page should be accessible from:
>         http://www.redland.opensource.ac.uk/docs/api/parser.html
> 
> It says:
>         base_uri: the base URI to use (or NULL if the same) 
> 
> But I got a segfault then $base_uri was undef (in perl).
> 
> It says:
>         Return value: librdf_stream of statements or NULL
> 
> But I got a segfault instead of undef then file not found.

OK - another recorded bug.

That doc is the bare bones that is expanded in the perl version:
  http://www.redland.opensource.ac.uk/docs/pod/RDF/Parser.html

but the phrase "with optional base RDF::URI BASE_URI" is obviously
not working.  Noted.

> Yes. I just thought that you maby did that.  It just seemed
> uneccessary work to convert a file path to a correct file url just to
> have it converted back again.
> 
> And it is customary in Perl to provide a way to read directly from a
> filehandle instead of a temporary file.  That would be much better for
> large files or slow connections.


Redland (C) reading from a Perl file handle.  Cross-language stuff
like that is *hard* to do portably.  I'm presently working out how to
do perl calling C calling perl in order to do callbacks.  And change
perl to python, tcl, java ...


> I said: I would like to *separate* the modules.  I just want the
> parser.  I think it's great that you have a frontend for several
> parser plugins.  That module *should* be named RDF::Parser, and be
> uploaded on CPAN.
> 
> And RDF::Stream, RDF::Statement and RDF::Node must come with the
> parser.  But maby they should be called RDF::Parser::Stream,
> RDF::Parser::STatement, etc.

I'm considering making Redland run on CPAN but won't grab any top
level RDF:: modules since there is no agreement on their interface.

If you just want the parser interface, tough, Redland is more than
just a parser.  I could write a perl wrapper for Rapier, maybe I'll
look at.


> I don't see the necessity for a special RDF::URI, since there is a
> good perl URI module in existence.

The RDF::URI is a Redland URI - portable among languages.  Again how
would Redland's URI class (in C) get access to Perl objects.  I think
I made convience methods somewhere so you can just use perl URIs
objects wherever a Redland one is used.  Have to check that.

> 
> > All the above applies to other Redland language interfaces - Python,
> > Tcl, C.
> 
> Yes.  I guess that it may be a little complicated to integrate with
> Perl and at the same time have it general for several languages.

You bet.  Nearly as much pain as getting expat/libxml and Berkeley DB
linking issues sorted.


> How much is realy needed for just the RDF parser interface?
> 
> I'm looking for soemthing like DBI or the Template module in
> construction.

Not much.

> I searched for some Perl APIs a few days ago:
>         http://uxn.nu/wraf/implementations.html
> 
> Maby libgnurdf could be something?  I haven't seen it before.

Redland is GNU librdf.  In fact it installs as librdf.a

Never seen that before, seems to be an RDF app. of XML DOM.

Dave