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We should remember that there's a reason entity resolution is not
required in XML. The spec states:
This rule is based on the recognition that the automatic inclusion
provided by the SGML and XML entity mechanism, primarily designed to
support modularity in authoring, is not necessarily appropriate for
other applications, in particular document browsing. Browsers, for
example, when encountering an external parsed entity reference,
might choose to provide a visual indication of the entity's presence
and retrieve it for display only on demand.
Tim Bray's annotated spec elaborates:
In discussion of external entities, we realized that the semantics
of external text entities (compulsory inclusion at the point where
they are encountered) are deeply incompatible with the desired
behavior of Web browsers. Consider the following example of the
beginning of an XML document:
<?xml version='1.0'?>
<!DOCTYPE doc [ <!ENTITY MSA SYSTEM
"http://www.microsoft.com/press/311.xml";>
<!ENTITY NSA SYSTEM
"http://home.netscape.com/PR/x27.xml";> ]>
<doc>Netscape today
announced that &NSA;. In response, Microsoft issued the following
statement: &MSA;. ...
A Web browser is typically making an aggressive effort to display
text to the user as soon as possible, in parallel with fetching it
from the network. In the example above, if a browser were required
to fetch and process all external entities, it could only display
the first four words before starting another network fetch
operation. To make things worse, bear in mind that the replacement
text for the entity NSA could well include other external entities
which in turn would need to be fetched.
This type of situation is unacceptable. Hence the rule that
non-validating parsers need not fetch external entities if they
don't want to.
These reasons apply equally well to XInclude as they do to external
entities. Browsers may choose not to load included elements.
--
+-----------------------+------------------------+-------------------+
| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
+-----------------------+------------------------+-------------------+
| XML in a Nutshell, 2nd Edition (O'Reilly, 2002) |
| http://www.cafeconleche.org/books/xian2/ |
| http://www.amazon.com/exec/obidos/ISBN%3D0596002920/cafeaulaitA/ |
+----------------------------------+---------------------------------+
| Read Cafe au Lait for Java News: http://www.cafeaulait.org/ |
| Read Cafe con Leche for XML News: http://www.cafeconleche.org/ |
+----------------------------------+---------------------------------+
|
