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Protocols : a look at the different approaches and draft evaluati ons

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Thu, 1 Jul 2004 16:22:19 +0100
Message-ID: <E864E95CB35C1C46B72FEA0626A2E80803616088@0-mail-br1.hpl.hp.com>
To: public-rdf-dawg@w3.org

We have two protocol suggested: Joseki's RDF WebAPI [1] and in N3QL [2].
Both are HTTP GET based, using the GET query string.


RDF WebAPI:
The request is "http://modelURL?lang=<langURI>&query=<queryString>".  The
result is the matching subgragh. It can take additional parameters such as
forcing the return of a result set as a graph.

N3QL:
The request is "http://serviceURL?<queryString>"  The result is the
constructed graph from the RHS of the "select".


The difference in approach is between naming the query service and naming
the query model.

N3QL has a URL to a query service, and so does not need to name the query
language.  Different query languages would appear as different query
services.  It is simple to say what features a query service has in an RDF
description because the query service has a URI.  It is hard to describe the
knowledge base characteristics - there is no name for the knowledge base
itself.

The RDF WebAPI names the model, and the service is identified by the
addition "lang=" parameters but does not have a proper URI.  It is hard to
describe features of the service because it does not have a URI; it is easy
to describe the knowledge base because it does have a URI (this helps in
extending to an update protocol because the knowledge base updated is
named).


3.8 Bookmarkable Queries
Both have URLs for requests so are bookmarkable and cacheable.

3.12 Streaming Results
Neither meet the streamability requirement.

4.4 User-specifiable Serialization
Both allow MIME type negotiation.

4.5 Aggregate Query
Both only allow one specified service.

4.7 Bandwidth-efficient Protocol
Content negotiation can request compression.

	Andy

[1] http://www.joseki.org/protocol.html
[2] http://www.w3.org/DesignIssues/N3QL#HTTP
Received on Thursday, 1 July 2004 11:22:36 GMT

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