xml-dev - Re: How to use binary data with XML?

[Chris Lilley <chris@w3.org>]

"Roger L. Costello" wrote:
> 
> I have a few questions on using binary data (e.g., gif, jpeg images)
> with XML.
> 
> (1)  Binary data isn't actually put in an XML file, correct? i.e., the
> binary data is _not_ inline, correct?  

Not usually, although it is arguable (in terms of document object
modelks) that notation does exactly that; however in practice no, you
don't physically put jpeg-compressed bytes into the middle of your
document instance.

> An XML file just contains ASCII text, correct?

No, and XML file contains  Unicode text, which is one reason why lieral
insertion of binary data would be difficult.

> 
> (2)  Just like in HTML, binary data is _referenced_ by the XML document,
> correct?

That is the most sensible way to do it, It allows independent revision,
and independent re-use, and facilitates cacheing.

> 
> (3) Is this the correct way of using binary data:
> 
> DTD:
> 
> <!NOTATION jpeg PUBLIC "JPEG">
> <!NOTATION gif PUBLIC "GIF">
> 
> <!ENTITY bostonGIF SYSTEM "http://www.maps.com/boston.gif" NDATA gif>
> <!ENTITY bostonJPEG SYSTEM "http://www.maps.com/boston.jpeg" NDATA jpeg>
> 
> <!ELEMENT map (image)>
> <!ELEMENT image EMPTY>
> <!ATTLIST image
>               src  ENTITY #REQUIRED
>               desc CDATA  #IMPLIED>
> 
> XML:
> 
> <map>
>     <image src="bostonGIF"
>            desc="Map of Boston"/>
> </map>

Its one way. It works in some viewers. Its rather sub-html, though -
there is no content, not even a measly alt attribute, let along actual
structured text alternatives.

--
Chris

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