Some consideration about the xerces DOM implementation 2007-04-18 - By Dick Deneer
I am using the xerces parser and Dom implementation as the base of a
simple XML editor.
The editor has a source and a tree (DOM) view.
Using the DOM in an editor requires other functionalitiy then just
using a DOM for showing or validating purposes.
In fact there are two issues with the current implementation, making
it very hard to use xerces for this purpose.
1. It may be clear that it is important that the user gets the same
(or nearly the same) xml after switching from source to DOM and back.
2. The user don't want unexpected additions or mutations in the DOM
while editing or validating.
I will give some examples:
· It is not possible store entity references in attribute values
when building a DOM, making is impossible to get the original XML
back after serializing. There is a jira issue for this problem, see
https://issues.apache.org/jira/browse/XERCESJ-1225
· The DOMNormalizer adds default required attributes to the DOM
tree. Altough perfectly right according to the official
specifications, this is not desired for the use in an editor.
· First it will produce a error message "cvc-complex-type.4:
Attribute 'xxxxx' must appear on element 'yyyyyy', which is in fact
not valid anymore, because the problem is already solved by the
DOMNormalizer, and secondly the XML is not the same anymore. These
two things are confusing for the user. At this moment it is not
happening for elements , but It looks like the same behavior is going
to be implemented.
· Adding a textNode which is adjacent to another, will
immediately be delete by the DOMNormalizer. Again, this may be
perfectly right, but confusing for a user when editing in a DOM. And
it is not possible to validate the DOM without this "side-effect".
Feedback of what happend is given by all kind of document events,
which is great to still give some explanation to the user and keep
trees in sync. But I would prefer to let some things not happen
and be in control in the front.
I really hope that in the future xerces will bring more "features or
properties" to control the behavior of the DOMParser and DOMNormalizer.
D. Deneer
<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line
-break: after-white-space; "><P style="margin: 0.0px 0.0px 16.0px 0.0px">I am
using the xerces parser and Dom implementation as the base of a simple XML
editor.</P><P style="margin: 0.0px 0.0px 16.0px 0.0px">The editor has a source
and a tree (DOM) view.</P><DIV style="margin-top: 0px; margin-right: 0px;
margin-bottom: 16px; margin-left: 0px; "> <BR class="khtml-block-placeholder"><
/DIV><P style="margin: 0.0px 0.0px 16.0px 0.0px">Using the DOM in an editor
requires other functionalitiy then just using a DOM for showing or validating
purposes.</P><P style="margin: 0.0px 0.0px 16.0px 0.0px">In fact there are two
issues with the current implementation, making it very hard to use xerces for
this purpose.</P><P style="margin: 0.0px 0.0px 16.0px 0.0px">1. It may be clear
that it is important that the user gets the same (or nearly the same) xml after
switching from source to DOM and back.</P><P style="margin: 0.0px 0.0px 16.0px
0.0px">2. The user don't want unexpected additions or mutations in the DOM
while editing or validating.</P><DIV style="margin-top: 0px; margin-right: 0px;
margin-bottom: 16px; margin-left: 0px; "> <BR class="khtml-block-placeholder"><
/DIV><P style="margin: 0.0px 0.0px 16.0px 0.0px">I will give some examples:</P>
<P style="text-indent: -24px;margin-top: 0px; margin-right: 0px; margin-bottom:
16px; margin-left: 24px; "><FONT class="Apple-style-span" face="Symbol">·</FONT
> It is not possible store entity references in attribute values when
building a DOM, making is impossible to get the original XML back after
serializing. There is a jira issue for this problem, see <A href="https:/
/issues.apache.org/jira/browse/XERCESJ-1225"><FONT class="Apple-style-span"
color="#000CEE">https://issues.apache.org/jira/browse/XERCESJ-1225</FONT></A><
/P><P style="text-indent: -24px;margin-top: 0px; margin-right: 0px; margin
-bottom: 16px; margin-left: 24px; "><FONT class="Apple-style-span" face="Symbol"
>·</FONT> The DOMNormalizer adds default required attributes to the DOM
tree. Altough perfectly right according to the official specifications, this is
not desired for the use in an editor. </P><P style="text-indent: -24px;margin
-top: 0px; margin-right: 0px; margin-bottom: 16px; margin-left: 24px; "><FONT
class="Apple-style-span" face="Symbol">·</FONT> First it will produce a
error message "cvc-complex-type.4: Attribute 'xxxxx' must appear on element
'yyyyyy', which is in fact not valid anymore, because the problem is already
solved by the DOMNormalizer, and secondly the XML is not the same anymore.
These two things are confusing for the user. At this moment it is not
happening for elements , but It looks like the same behavior is going to be
implemented.</P><P style="text-indent: -24px;margin-top: 0px; margin-right: 0px
; margin-bottom: 16px; margin-left: 24px; "><FONT class="Apple-style-span" face=
"Symbol">·</FONT> Adding a textNode which is adjacent to another, will
immediately be delete by the DOMNormalizer. Again, this may be perfectly right,
but confusing for a user when editing in a DOM. And it is not possible to
validate the DOM without this "side-effect".</P><P style="margin: 0.0px 0.0px
16.0px 0.0px; font: 16.0px Helvetica; min-height: 19.0px"><BR></P><P style=
"margin: 0.0px 0.0px 16.0px 0.0px">Feedback of what happend is given by all kind
of document events, which is great to still give some explanation to the user
and keep trees in sync. But I would prefer to let some things not happen and
be in control in the front.</P><P style="margin: 0.0px 0.0px 16.0px 0.0px">I
really hope that in the future xerces will bring more "features or properties"
to control the behavior of the DOMParser and DOMNormalizer. </P><DIV style=
"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font:
normal normal normal 16px/normal Helvetica; min-height: 19px; "><BR></DIV><DIV
style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px
; ">D. Deneer</DIV></BODY></HTML>
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