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From Andy Seaborne <>
Subject Re: Setting a read limit when parsing a Graph
Date Thu, 16 Aug 2012 08:07:40 GMT

On 14/08/12 13:09, Reto Bachmann-Gmür wrote:
> Hi Alessandro,
> Two things:
> - the mark method doesn't truncate the stream after the indicated number of
> bytes, but makes sure that within the indicated number of bytes one can
> reset the stream back to that position. If one reads more than the
> indicated number of bytes the mark becomes invalid (i.e. reset won't work)
> but otherwise the stream behaves as normal.
> - I'mm not sure how the jena parser works and if you get the triples read
> so far if your rdf/xml is truncated. You might want to truncate n-triples
> after a dot.

The parser streams and emits triples as they are completed.  All the 
parsers do.

Which Jena parser framework does Clerezza use?  The old one or the new 
one?  The new one, RIOT, has an interface for receiving a stream of 
triples.  (You can do this in the old one but you need to write a small 
graph implementation.)

Reto - we're moving towards switching from the old jena-core readers to 
a new reader framework which does better content negotiation, uses the 
(much) faster parsers from RIOT and is properly extensible.  Igf you 
have any input, then mailto:dev@jena.a.o

Alessandro - if you can open the file twice, something like this might work:

read in 1240 bytes and then parse just that.  Then close-reopen the file 
to read the whole thing.


> Cheers,
> Reto
> On Tue, Aug 14, 2012 at 1:53 PM, Alessandro Adamou <>wrote:
>> Hi,
>> I need to write a function that performs lookahead of the OWL ontology ID
>> for a Graph, therefore it has to scan the content up to a certain point to
>> see if it has found an ontology IRI / version IRI pair.
>> I thought that setting mark() on a BufferedInputStream did the trick,
>> something like:
>> MGraph graph = new SimpleMGraph();
>> BufferedInputStream bIn = new BufferedInputStream(content);
>> bIn.mark(1240); // Read up to 1k
>> parser.parse(graph, bIn, SupportedFormat.RDF_XML);
>> (parser has a Jena parser provider registered)
>> But apparently this is not working. Even for streams much longer than 1
>> kiB, with the interesting triples right at the very end, these triples are
>> always found.
>> Do the Clerezza parser override the marks on a buffered stream, or maybe
>> Jena is doing so? Or even better, am I doing this wrong?
>> Best,
>> -- Alessandro
>> --
>> M.Sc. Alessandro Adamou
>> Alma Mater Studiorum - Università di Bologna
>> Department of Computer Science
>> Mura Anteo Zamboni 7, 40127 Bologna - Italy
>> Semantic Technology Laboratory (STLab)
>> Institute for Cognitive Science and Technology (ISTC)
>> National Research Council (CNR)
>> Via Nomentana 56, 00161 Rome - Italy
>> "I will give you everything, just don't demand anything."
>> (Ettore Petrolini, 1917)
>> Not sent from my iSnobTechDevice

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