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Re: Streamability II

From: Janne Saarela <janne.saarela@profium.com>
Date: Wed, 16 Jun 2004 15:45:02 +0300
Message-ID: <40D040CE.6090706@profium.com>
To: "Seaborne, Andy" <andy.seaborne@hp.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

> With a streamable protocol the loop above can be executed the first time as
> soon as the first result binding (row in the result table) arrives.  This is
> Jim's example of do something with first 100 results while the server is
> still dealing with the next 100 done in the style of iterators.  The above
> code does nto require all the results to be in memory at the same time.

Agreed, this would be familiar for developers who've been dealing SAX
programming model.

> In Jena the classes are: QueryResults [1] for the iterator and ResultBinding
> [2] for each row of the conceptual result table.
> 
> [1]
> http://jena.sourceforge.net/javadoc/com/hp/hpl/jena/rdql/QueryResults.html
> [2]
> http://jena.sourceforge.net/javadoc/com/hp/hpl/jena/rdql/ResultBinding.html
> 
> See also java.sql.ResultSet.  The API style is to deliver one row of the
> result set to the application at a time with java.sql.ResultSet#next() &
> java.sql.ResultSet#isLast() Result set can be TYPE_FORWARD_ONLY.

This may be too concrete an example but pls bear with me as I need
to understand how this would work in practice:

I can imagine applications blocking with a call to next() even
if isLast() says 'false'. This is not what I want query clients
to experience (e.g. network problem would hang a program until
TCP level says 'timeout').

If the call to next() is asyncronous, I guess we would then need
a good'old select() type of call familiar to C programmers
who've dealt with file descriptors.

Bottom line question: will the streaming protocol effectively
require more work from developers? I cannot see how to map
it to current practice of using ResultSets and alike without
additional low level IO management?

I am sure if someone with ODBC experience could tell how this
gray area (for me) was solved I would feel more comfortable.

Janne
-- 
Janne Saarela <janne.saarela at profium.com>
Profium, Lars Sonckin kaari 12, 02600 Espoo, Finland
Internet: http://www.profium.com
Received on Wednesday, 16 June 2004 08:45:09 GMT

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