Martin J. Duerst wrote:
Makoto, I think the things you have mentioned in your mail are quite
important.
But my guess is that many of the participants in this discussion don't have
the necessary background. Is there somewhere a web page where all these terms
are defined and explained with simple examples, or something similar?
I am obsessed by XML...
Here is an imprecise-but-not-totally-inappropriate analogy.
XML documents are source programs. External DTD subsets are
header files that contain declarations and are referenced
at the beginning of XML documents (note: at most one external
DTD subset is referenced by one XML document).
External parsed entities are include files that contain source
program fragments and are referenced in the middle of XML documents.
External parameter entities are include files that contain declarations
and are referenced by external DTD subsets.
XML document ----------------> external DTD subset
| |--> external parameter entity
|
|--> external parsed entity
The BNF for XML documents and that for external DTD subsets are quite
different. On the other hand, some external parsed entities are
legal XML documents, and some external parameter entities are legal
external DTD subsets.
Viewers for XML documents and viewers for external DTD subsets are
quite different.
(Please forgive my white lie. I think that this is enough for our
discussion. > XML experts)
If you would like to know the truth, the best document on the WWW is
Tim's annotated XML. Its URL is:
http://www.xml.com/axml/testaxml.htm
DTDs, external DTD subsets, and internal DTD subsets are defined in
2.8 of XML 1.0 (http://www.xml.com/axml/target.html#dt-doctype)
[Definition:] The XML document type declaration contains or
points to markup declarations that provide a grammar for a class of
documents. This grammar is known as a document type definition, or
DTD. The document type declaration can point to an external subset (a
special kind of external entity) containing markup declarations, or
can contain the markup declarations directly in an internal subset,
or can do both. The DTD for a document consists of both subsets taken
together.
Entitites are defined in Section 4 of XML 1.0.
(http://www.xml.com/axml/target.html#sec-physical-struct)
Parameter entity
[Definition:] Parameter entities are parsed entities for use within the
DTD. These two types of entities use different forms of reference and
are
recognized in different contexts. Furthermore, they occupy different
namespaces; a
parameter entity and a general entity with the same name are two
distinct
entities.
Parsed entity
Entities may be either parsed or unparsed. [Definition:] A parsed
entity's
contents are referred to as its replacement text; this text is
considered an
integral part of the document.
Hope this helps.
Cheers,
Makoto
Fuji Xerox Information Systems
Tel: +81-44-812-7230 Fax: +81-44-812-7231
E-mail: murata(_at_)apsdc(_dot_)ksp(_dot_)fujixerox(_dot_)co(_dot_)jp