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Re: SGML Entities or Web-style objects in XML?



On Sat, 21 Sep 1996 16:13:47 -0400, Paul Prescod
<papresco@calum.csclub.uwaterloo.ca> wrote:

Jon says we're not to discuss this subject now, but so many erroneous
impressions of SGML have been created that I feel a need to get the facts
straight.

>Before we get too far into a discussion of entities, I'd like to take a
>second to reflect on XML's dual parentage. (risking Len's ire =) ) 
>
>  The SGML Way:
>
>In the SGML world, entity referncing and document parsing are intertwined,
>though separate. 
(snip)

>  The Web Way:
>
>In the Web world (especially in the HTML world), entities (or "objects")
>are, conversely, resolved by the application AFTER parsing. 

SGML has entity types for both of these "ways".

The SGML Way:

 SGML text entities, internal and external, are accessed and parsed in context,
as though their replacement text was physically in the entity from which  they
are referenced.

The Other SGML Way (aka the Web Way, but we did it first):

External data entities, whether CDATA, SDATA, or NDATA, are *never* parsed in
context. The application is given a pointer to them and it can request access or
not, as it sees fit. When accessed, parsing is based on the data content
notation, which may or may not be SGML.

SUBDOC entities are treated like CDATA external data entities with SGML as the
notation. They are not automatically parsed in context.

And just for the record, whether an external entity is located via a public
identifier or a system identifier is totally independent of what kind of text is
in the entity.
--
Charles F. Goldfarb * Information Management Consulting * +1(408)867-5553
           13075 Paramount Drive * Saratoga CA 95070 * USA
  International Standards Editor * ISO 8879 SGML * ISO/IEC 10744 HyTime
 Prentice-Hall Series Editor * CFG Series on Open Information Management
--


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