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https://issues.apache.org/jira/browse/XALANJ-2691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17758864#comment-17758864
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Mukul Gandhi commented on XALANJ-2691:
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@Joseph, you wrote one of the following points : 'since the switch from DTM
iterators to XCI cursors is nearly a 1:1 mapping'.
Following is what I've gathered about this topic,
If you're inclined to suggest something like replacing XalanJ DTM nomenclature,
to that of XCI (i.e, XML Cursor Interface), I guess the least that may be done
within XalanJ codebase, is to refactor the interfaces (i.e, their names)
DTM.java and DTMIterator.java to XCI.java and XCIIterator.java respectively.
There seems to be various other DTM related Java interfaces and classes that
may be present within XalanJ codebase, and they may need to be renamed from
*DTM*.java to *XCI*.java. It may also be required, to change XalanJ codebase
documentation to have string text references like XCI from DTM.
I guess, all of these refactorings within XalanJ codebase, shall significantly
change many Java interface, class and perhaps method names, therefore
implementing these XalanJ codebase refactoring, needs to be done carefully and
tested before committing them to XalanJ repos.
You may let us know, if you'd have any thoughts on these points.
> Refactor: Replace direct DTM reference with XCI
> -----------------------------------------------
>
> Key: XALANJ-2691
> URL: https://issues.apache.org/jira/browse/XALANJ-2691
> Project: XalanJ2
> Issue Type: Wish
> Security Level: No security risk; visible to anyone(Ordinary problems in
> Xalan projects. Anybody can view the issue.)
> Components: DOM, DTM, JAXP, Xalan, Xalan-interpretive, XSLTC
> Reporter: Joseph Kessselman
> Assignee: Gary D. Gregory
> Priority: Minor
> Original Estimate: 2,400h
> Remaining Estimate: 2,400h
>
> DTM was never intended to be a general interface to document models. It was a
> specific solution for cramming as large a document as possible into the
> limited resources available in PCs around the year 2000.
> We have been able to create DTM proxy layers for other data sources –
> databases, for example – but they are uniformly ugly and inefficient code.
> A better solution, which I implemented in IBM's internal derivative of Xalan
> and hoped to contribute back to Apache, was to make DTM _only_ a data model,
> and access it through a set of cursor-object interfacesI named XCI (XML
> Cursor Interface ... IBM does love its three-letter initialisms). These
> slotted in essentially where the DTM Iterators sit now, but provided complete
> encapsulation of the data implementation –- all access to a node was via an
> XCI cursor currently pointing to that node, with no DTM artifacts leaking
> through.
> The advantage is the obvious one: XCI can be efficiently implemented
> _directly_ over data models (DTM, DOM, database, custom data trees in any
> representation, potentially directly over Java reflection...), without
> needing to build a map to DTM node numbers. Little to no efficiency is lost
> accessing DTM, as the DTM implementation of the XCI is essentially a
> repackaging of DTM iterators. Efficiency gains, and as importantly
> ease-of-implementation gains, for other back-end models are significant.
> For models which are general networks rather than trees there is risk of
> getting into loops; stylesheets can be written to avoid that, or the XCI
> implementation can have some mechanism to break those potential loops; in any
> case, Xalan already has protection against unreasonably deep recursion so
> those will be caught and reported.
> I had hoped to donate this improvement back to Apache. Unfortunately, at the
> same time I was doing this, the IBM XSLT processor was undergoing other major
> rewrites to build a true optimizing compiler as replacement for XSLTC, which
> we were not ready (willing?) to contribute to Apache and I didn't have a
> chance to disentangle the two.
> Having done it once: It *is* a big rewrite task. Not an insanely complicated
> one, since the switch from DTM iterators to XCI cursors is nearly a 1:1
> mapping,. But even with experience I'd say 3 months of full-time work
> minimum; possibly much more. And it's been long enough that I'd have to
> redevelop it de novo – which is not a bad thing, as I'm not sure who, if
> anyone, in IBM could be persuaded to donate the XCI I created for them.
> I have set the initial priority as {_}*minor*{_}; Xalan can certainly
> continue as it is, with DTM as the (ugly) glue layer, and we've got lots of
> higher-severity items stacked up on the backlog. However, if we had the
> resources we once did (with people actually paid to work on Xalan), I believe
> this is a significant improvement in Xalan architecture and would be worth
> investing in. Certainly if anyone attempts a true Xalan 3.0 (as opposed to a
> Xalan 2.x that supports part or all of XSLT 3.0), this should be part of the
> effort.
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