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Re: SPARQL 1.1 Protocol: Format of fault messages

From: Eric Prud'hommeaux <eric@w3.org>
Date: Sun, 3 Oct 2010 17:05:12 -0400
To: Richard Cyganiak <richard@cyganiak.de>
Cc: public-rdf-dawg-comments@w3.org
Message-ID: <20101003210511.GA21628@w3.org>
* Richard Cyganiak <richard@cyganiak.de> [2010-10-03 21:40+0100]
> Eric,
> 
> If you write in the spec that they should serve XHTML, then they
> will serve you tag soup. This is not a realistic option.

what if i say it's XML which happens to parse as HTML?
honestly, i don't care if it has a video element and captions
and over-uses <smellorama/> tags; i just want an ID i can grab
with my XML parser.


> Richard
> 
> 
> On 3 Oct 2010, at 21:08, Eric Prud'hommeaux wrote:
> 
> >* Richard Cyganiak <richard@cyganiak.de> [2010-10-03 19:36+0100]
> >>On 3 Oct 2010, at 17:03, Eric Prud'hommeaux wrote:
> >>>I read that as you're OK with the SOAP binding specifying a
> >>>SOAP fault
> >>>which is different from the HTTP bindings, so
> >>><malformed-query/> stays
> >>>as is.
> >>
> >>I don't know what a SOAP fault is. I'm just concerned with the HTTP
> >>bindings.
> >>
> >>>>Saying that you SHOULD use a certain format leaves enough wiggle
> >>>>room for implementors to innovate, IMO.
> >>>
> >>>Sure, but we'd also like to encourage a backwards-compatible
> >>>extensibility model which allows me to have a great new idea without
> >>>breaking all the old code which e.g. reports errors to humans.
> >>>>
> >>>
> >>>>I have no objection against also proposing alternative response
> >>>>formats, as long as one option is clearly highlighted as the “no-
> >>>>brainer” option.
> >>>
> >>>And I'm interested in making sure that the alternatives subsume the
> >>>no-brainer in a way that the no-brainer parser can use.
> >>
> >>Fair points.
> >>
> >>>>And RDFa would be better than a magic class name.
> >>>
> >>>I'm afraid of demanding a generic RDFa parser for consumers of error
> >>>messages.
> >>
> >>I see your point. But I'm afraid of even demanding an XHTML parser.
> >>In reality, too much XHTML ends up as tag soup.
> >
> >I think the XML parser they use for the SPARQL Results will be fine.
> >If they were using DOM to parse, they can getElementById; if they're
> >using SAX, they can:
> >
> >public void startElement(String namespaceURI, String localName,
> >                        String qName, Attributes atts) throws
> >SAXException {
> >   userMessage = false;
> >   for (int att = 0; att < atts.getLength(); att++) {
> >	if (atts.getLocalName(att) == "id" &&
> >	    atts.getValue(att) == "malformedQueryFault") {
> >	    userMessage = true;
> >	}
> >   }
> >}
> >
> >public void characters(char[] ch, int start, int length) throws
> >SAXException {
> >   if (userMessage)
> >	...
> >
> >Either way, I think that the additional client code required to get
> >the user message is between 1 and 10 lines. For user code, they
> >already have some way to entity-encode text so it's basically
> >   print(template.top + entityEncode(errorMessage) + template.bottom);
> >
> >
> >>How about this:
> >>
> >>[[
> >>A malformedQueryFault response SHOULD be a text/plain document
> >>containing a human-readable representation of the error. For
> >>example:
> >>
> >>  HTTP/1.1 400 Bad Request
> >>  Content-Type: text/plain
> >>  Content-Length: 37
> >>
> >>  Parse error at [5:17], unexpected ' '
> >>
> >>Conformant implementations MAY convey the error message using
> >>other formats than text/plain. If they do so, or include more
> >>content besides the one-line error message in a text/plain
> >>response, then they MUST include a one-line human-readable
> >>representation of the error as an X-Malformed-Query-Fault HTTP
> >>header:
> >>
> >>  HTTP/1.1 400 Bad Request
> >>  Content-Type: application/xhtml+xml
> >
> >+1 to inlcuding the header in the example. We can just use text/html
> >and every browser on the planet will handle it.
> >
> >
> >>  X-Malformed-Query-Fault: Parse error at [5:17], unexpected ' '
> >
> >Interesting, I could see doing this if the client's error-parsing
> >burden were higher, but I've pretty much convinced myself (above)
> >that it's easy (especially compared to getting at headers when I'm
> >running as a CGI, servlet, webkit client, etc.).
> >
> >
> >>  <?xml version="1.0" encoding="UTF-8"?>
> >>  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0//EN"
> >>"http://www.w3.org/MarkUp/DTD/xhtml.dtd">
> >>  <html xmlns="http://www.w3.org/1999/xhtml">
> >>    <head>
> >>      <title>Malformed Query</title>
> >>    </head>
> >>    <body>
> >>      <h1>Malformed Query</h1>
> >>      <pre id="malformedQueryFault">Parse error at [5:17],
> >>unexpected ' '</pre>
> >>    </body>
> >>  </html>
> >>]]
> >>
> >>
> >>Advantages:
> >>
> >>1. Anyone can still do anything, as long as they include one
> >>HTTP header
> >>2. Machine-readability is *always* given
> >
> >but via heuristics; I have to have two handlers.
> >
> >
> >>3. Backwards compatible: If a client checks for presence of the
> >>header, and if absent checks for a text/plain body, then it will
> >>always get the message.
> >
> >My first interpretation was that you should give plain text, but if
> >you weren't content with that, maybe something like this HTML here...
> >I now understand that this is to encourage exactly one of these two
> >alternatives.
> >
> >While this does allow me to convey structured info while still giving
> >nice-to-read info to the primitive clients, I don't think that the
> >text/plain avoids much effort. The clients will still need to
> >implement both and the servers have a trivial amount of work to do to
> >implement the XHTML. I think the net work is lower, and the protocol
> >is simpler, if the only SHOULD is the XHTML alternative.
> >
> >
> >
> >>Best,
> >>Richard
> >>
> >>
> >>
> >>
> >>>(Of course, I'm happy to see that practice flourish on its
> >>>own.) Class was a poor choice, how about ID? New proposal:
> >>>
> >>>[[
> >>>A malformedQueryFault response SHOULD be an XHTML document in
> >>>which an
> >>>element with an XML ID of <code>malformedQueryFault</code> conveys a
> >>>human-readable representation of the error. For example:
> >>>
> >>><?xml version="1.0" encoding="UTF-8"?>
> >>><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0//EN"
> >>>"http://www.w3.org/MarkUp/DTD/xhtml.dtd">
> >>><html xmlns="http://www.w3.org/1999/xhtml">
> >>> <head>
> >>>   <title>Malformed Query</title>
> >>> </head>
> >>> <body>
> >>>   <h1>Malformed Query</h1>
> >>>   <pre id="malformedQueryFault">Parse error at [5:17],
> >>>unexpected ' '</pre>
> >>> </body>
> >>></html>
> >>>
> >>>Other HTML elements in the response do not change the interpretation
> >>>of the element with the XML ID of <code>malformedQueryFault</code>/
> >>>]]
> >>>
> >>>
> >>>>Best,
> >>>>Richard
> >>>
> >>>-- 
> >>>-ericP
> >>
> >
> >-- 
> >-ericP
> 

-- 
-ericP
Received on Sunday, 3 October 2010 21:05:49 GMT

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