| Re: Another XML Question [message #43225 is a reply to message #43081] |
Thu, 24 March 2005 09:21   |
JD Smith
Messages: 850
Registered: December 1999
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Senior Member |
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On Thu, 24 Mar 2005 09:19:39 -0700, Karl Schultz wrote:
> On Wed, 23 Mar 2005 19:44:03 -0800, kuyper wrote:
>
>> Michael Wallace wrote:
>>>> Oh, of course. Now what the hell is a DTD again?
>>>
>>> Document Type Definition.
>>> ...
>>> [Lots of good general-purpose information about DTDs]
>>
>> David's questions got me curious, so I spent a lot of time this
>> afternoon wading through the IDL documentation for it's XML objects. At
>> the end of that survey, I still couldn't figure out how to use a DTD in
>> connection with those objects. There's lots of things that say "if a
>> DTD is provided", but I couldn't find anything that indicated how to
>> provide a DTD. Could someone give some actual IDL code for this?
>
> It is actually rather automatic and you don't really need IDL code for it.
>
> DTD's are actually "provided" by the XML doc itself referencing a DTD. If
> it does so and the VALIDATION_MODE keyword to IDLffXMLDOMDocument::Init or
> Load is set to 1, then the parser will validate the document using the
> DTD, if one is available.
>
> In the example below, note the DOCTYPE element. It refers to a file named
> slideshow.dtd that contains the DTD, also shown below. The DTD info can
> actually be in the XML file itself, within the DOCTYPE element, but it is
> common to put the DTD in a different file for easier reuse.
>
> When VALIDATION_MODE is 1, the parser will check the XML against the DTD
> and throw a parse error if the XML does not conform to the DTD. This is a
> HUGE deal when writing IDL code to parse the XML. If you know the XML doc
> passed the validation step, you can make tons of safe assumptions in your
> parser code and get to the job at hand. If you don't validate, your
> parser needs to be robust enough to deal with what might be a totally
> random XML file. Like, I could pass an XML file describing the channel
> lineup for my PVR to David's app that is expecting some special type of
> configuration data. It would be easier to let the parser throw a parse
> error than to write IDL code to discover the mistake.
I can't help but wonder here how much more quickly David would have
progressed if his input file had been a simple text file like:
file config.txt
=====================
CAMPAIGN_ID: 0
SPAM_WAIT: 60
HEARTBEAT_TIME: 60
=====================
I bet he could have had that file parsing in 10 seconds or less. XML is
nice. Overusing XML to be buzzword compliant, not so nice.
JD
> ++++++
>
> Here is the example :
>
>
> <?xml version='1.0' encoding='us-ascii'?>
>
> <!-- A SAMPLE set of slides -->
>
> <!DOCTYPE slideshow SYSTEM "slideshow.dtd">
>
> <slideshow
> title="Sample Slide Show"
> date="Date of publication"
> author="Yours Truly"
>>
>
> <!-- PROCESSING INSTRUCTION -->
> <?my.presentation.Program QUERY="exec, tech, all"?>
>
> <!-- TITLE SLIDE -->
> <slide type="all">
> <title>Wake up to WonderWidgets!</title>
> </slide>
>
> <!-- OVERVIEW -->
> <slide type="all">
> <title>Overview</title>
> <item>Why WonderWidgets are great</item>
> <item/>
> <item>Who buys WonderWidgets</item>
> </slide>
>
> <slide type="exec">
> <title>Financial Forecast</title>
> <item>Market Size < predicted!</item>
> <item>Anticipated Penetration</item>
> <item>Expected Revenues</item>
> <item>Profit Margin </item>
> </slide>
>
> </slideshow>
>
> The DTD (in file slideshow.dtd):
>
> <?xml version='1.0' encoding='us-ascii'?>
>
> <!--
> DTD for a simple "slide show".
> -->
>
> <!ELEMENT slideshow (slide+)>
> <!ATTLIST slideshow
> title CDATA #REQUIRED
> date CDATA #IMPLIED
> author CDATA "unknown"
>>
> <!ELEMENT slide (image?, title, item*)>
> <!ATTLIST slide
> type (tech | exec | all) #IMPLIED
>>
> <!ELEMENT title (#PCDATA)>
> <!ELEMENT item (#PCDATA | item)* >
> <!ELEMENT image EMPTY>
> <!ATTLIST image
> alt CDATA #IMPLIED
> src CDATA #REQUIRED
> type CDATA "image/gif"
>>
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