Subject: Re: [xsl] How to View Entity Reference From: David Carlisle <davidc@xxxxxxxxx> Date: Thu, 14 Sep 2006 14:24:44 +0100 |
> Yes, reading around briefly it seems that's how it works, although it > looks like a really bad idea. Surely a legacy thing? (or is it widely > used and I'm just blinkered?) TEI (who invented much of what's now standard linking practice, xpath-like path navigation, etc:-) use it a lot, not sure where else it's used these days. It's not such a bad idea really, if you go <img href="foo.jpg"/> you are supposed to just know by some out of band knowledge that the incoming data is a jpeg file (assuming your smart content negotiating web server doesn't decide to send you an svg instead:-) But NDATA entities are designed to allow you to formally declare entities to be associated with specific types of things > ".\Equations\008x0001.jpg" NDATA jpg>]> so you know that file is of type jpg and if you wish you can define <!NOTATION jpg PUBLIC "-/some formal identifier for the JPRG Standard"> So given some standard set of FPIs for image types (or link types or anything else) a document can unambiguously decalre what stuff it depends on (of course if you wish you can identify things in NOATION using a SYSTEM identifier and a URI (eg a namespace name) rather than an FPI) Of course if you _have_ got a world wide web and content negotation and stuff, while formally declaring types of files is nice if it's right, it's not nice at all if the types are wrong because you never really know what type you will get until you ask. Also if it turns out that in fact your browser can handle <img src="foo.anything"/> for all sorts of file types using 3rd party graphics filters and plugins and stuff, perhaps the early xml transformation stages really don't need to know anything about the file types involved and just treat everything as some opaque data that the end application will sort out, so NOTATION and unparsed entities are decidedly less popular than they were, and their cause wasn't helped when xsd schema botched the definition of NOTATION (claimed that they were just included in schema for compatibility with dtd, then made a definition which was incompatible with the dtd definition) Not that I'm a grumpy old sgml geek or anything, you realise... David
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