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   Re: [xml-dev] What is XML For?

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Alaric B. Snell wrote:
> On Thursday 24 October 2002 18:48, Paul Prescod wrote:
>>>Yes they are.  The locale database (timezones, month names, etc) on your
>>>Macintosh is all stored in Plist format and used by core libraries.
>>All of these libraries are under a single point of administrative
>>control. How do I define a purchase order schema for PLists that will be
>>used by thousands of independent processes?
> The same way you'd do it with XML, or TSV, or anything! XML doesn't make 
> interchange any easier. You still need to agree what XML structure to use, or 
> what column headings to use, or whatever.

Really? Here's (one way) I would do it in XML:

<!ELEMENT purchaseOrder (buyer, seller, ...)>

This is both human readable and computer processable. There are a 
variety of similar techniques. Now what's the equivalent for TSV, 
PLists, etc.?

>>Do you think that SAP and Quicken use the same object model for a
>>purchase order _internally_? Do you think that Word and Wordperfect have
>>the same internal model of a document? Do you think that CorelDraw and
>>Adobe FreeHand have the same internal model of a vector graphic?
> Yes, I think so. The only differences between them are incidental, and if 
> they all used the same file format for interchange then the only differences 
> would be names of fields. And if this file format was nice enough to have 
> automatic mapping into software objects, not even that!

I don't know where to go from here. It is unfathomable to me that the 
people at Corel would give up the opportunity to define in-memory data 
structures optimized for the algorithms that differentiate them from 
their competitors. Same for SAP, Quicken, Word, WordPerfect, etc.


>>Therefore I accept that when I write a vector graphics program, there
>>_will_ be an impedence mismatch between the file formats I must deal
>>with (under the control of standards bodies rather) and my internal
>>representation (under my control). Such is life.
> Not really! Quite a few 'standard' bitmap file formats are just dumps of the 
> memory structures used by the apps that first produced them - and they're all 
> roughly the same: header, palette, bitmap data. 

I'm talking about vector graphics programs. You're talking about bitmap 

> Sometimes you add extra pointers and indexing information when you load 
> something, when loading a text file it's quite common to slurp it into memory 
> as a character array but keep an array of indices of the starts of lines for 
> fast movement to a given character position. In almost all plain text 
> processing the in-memory and on-disk representations are *identical* with a 
> few extra pointers put in, maybe splitting lines out into a linked list at 
> worst.

Not in my experience. The text editor I worked on allowed Latin1 and 
even EBCDIC input but would never, ever use those encodings internally.

> I wouldn't say everyone disagrees with not using XML for stuff, it totalled 
> failed to take off in many industries I've seen. CSV still rules the wires 
> when it comes to exchanging databases, I'm afraid. We discontinued the option 
> of providing XML to our database because nobody used it.

"Providing XML to our database." I don't think you've been hearing what 
I've been saying about the kinds of applications XML is strong for. You 
are talking about dumping your internal model as XML. That's a marginal 
use of XML. If you and your competitors and partners need to get 
together and define a standard interchange format for structured, 
linked, perhaps-hierarchical data, I would be amazed if you found CSVs 
more convenient.

> They clearly do! The plists have been in use on macs for how long, Mr. 
> Blanchard? :-)

And today they are XML. ;)

> XML for data interchange has not filled a gaping need. An increased desire to 
> exchange data online came around, and XML was a hot new thing happening in 
> the W3C - aimed at replacing HTML on the Web at the time. So the people who 
> wanted to interchange data used XML. They would have done just as well had 
> XSLT and so on been developed on top of plists rather than XML, and maybe 
> better - plists have a richer basic data model, it's a tree with seperate 
> notions of key:value mappings and sequences rather than rolling both into one 
> (with the old problems of what to put in attributes and what to put in child 
> elements and mixed content and so on).

I'll ask again: what's the schema language for plists?

  Paul Prescod


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