Response to Simon St.L. on Entities v. XLL

Rick Jelliffe ricko at
Sun Nov 30 10:30:46 GMT 1997

> From: Simon St.Laurent <SimonStL at>

> The processing model we'd like to see for EMBED is very similar to that used 
> for a text entity, but it doesn't look like we'll be getting there soon.  
> Entities and NOTATIONs serve their purposes, but XML-Link seems far more 
> flexible, especially for our needs.

There is actually a fundamental difference in paradigm between XLL and entities

*  The SGML entity mechanism is based on having type information as part
of the declaration of the entity, not in the entity reference and not in the
entity itself.

*  The XLL mechanism (well, I should say the MIME mechanism really) is 
based on the entity being self-identifying as to type (aided by 
any additional attributes you like on the linking element).

The first way works best in heterogenous and dumb systems, and large systems
where you need to keep track of entities in one place (i.e. it is
moving constants to the prolog of the document).

The second way is more appropriate for the Web.  

So XML/XLL is very rich.  I think it is important to note that even
though XML is "SGML for the Web", it has always been assumed, I think, that
XML will be powerful enough to be more than just a delivery format--
it has entities, for example, to allow it to be used for simple
processing before and after it gets sent over the web.

Rick Jelliffe

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