Re: Momento and Cocoon [was Re: Jisp 3.0 moved to GPL licence]
Alan wrote:
* Daniel Fagerstrom [EMAIL PROTECTED] [2004-02-23 15:21]:
snip/
XSLT
A MomentoSource would also give a good way to use Momento together with
XSLT and XQuery in Cocoon. Here we need to extend the ordinary use of
sources somewhat, let me explain:
The Source interface provides a getInputStream method, in Cocoon some
Sources implements org.apache.excalibur.xml.sax.XMLizable that provides
a toSAX method as well. SAX or Streams are probably not the most
efficient way to communicate with an XML db, so to make the pseudo
protocol idea usable together with Momento, we should provide a way to
get a DOM structure from a pseudo protocol. This could be done by
introducing a new interface:
interface DOMizable {
org.w3c.domNode getNode();
}
Momento, with Cocoon in mind, lends itself to streaming.
Momento would readily support a read-only W3 DOM, but a read write
W3 DOM is quite ugly.
W3 DOM lets you to create inconsistant documents, with is not in
keeping with the C in ACID. (Examples if you want them.) There
is no way to specify the start and end of an atomic transcation
through the DOM API.
Momento uses XUpdate since one can specify a set of modifications,
and Momento can process those modifications as an atomic
transcation. XUpdate expresses all document modifications, and
does so declaratively. Momento can then make logic of you
intentions.
In a pipeline, XML input can be transformed into XUpdate
statement. I suppose one could an XUpdate using JXTemplate from
Flow as well.
XUpdate is really the method of choice for updating Momento.
Both XUpdate and SAX input are a good way to get data into
Momento.
I don't know if you and I talking about the same thing here, but
the sight of org.w3c.domNode leaves me cold. It is a nice
in-memory interface, but a poor interface for persistence.
If W3 DOM were the way to modify a Momento document, the
application developer would have to be prepared to catch all
kinda hel.., er, exceptions, since there are a bunch of stupid
things that Momento won't allow.
I only talked about read only access of DOM documents from XSLT, don't
worry ;)
or something similar. If the MomentoSource implements DOMizable, we have
direct access to nodes in the XML db.
Now we are prepared to connect Momento to XSLT. In Cocoon we can use
Saxon through the org.apache.cocoon.transformation.TraxTransformer, you
just need to change cocoon.xconf a little bit to use Saxon instead of
Xalan. There is also a TraxGenerator in the scratchpad that could be
used with some small modifications.
Momento connects to XSLT using a Saxon NodeInfo interface. It could
connect to Xalan just as easily (through read-only W3 DOM?).
Yes, that the idea. It can connect to Saxon through read only DOM as
well, don't know if there are any drawbacks with this though.
I would guess that Momento mainly would be accessed through the document
function in XSLT and XQuery. Saxon use JAXP 1.1 as external API to the
transformerand the URLs in the document functions are resolved by using
an implementation of javax.xml.transform.URIResolver that is provided by
the TraxTransformer.
The above is somewhat confusing for me. Momento does support the
JAXP API. XUpdate is implemented as a SAX filter. It seems like
Momento would work nicely in as a source, sink, or filter for
SAX events.
I've imagined that a pipeline would start with a Momento
document and an XSLT trasform or XQuery query.
Something along these lines:
map:match pattern=index.html
map:generate type=momento src=momento.mx
xslt=index-document.xslt/
map:transform type=xslt src=document-to-web.xslt/
map:serialize type=html/
/map:match
(It is easier for me to express myself as a Cocoon user.)
I rather propose:
map:match pattern=index.html
map:generate type=xslt src=momento:mydocument.mx
xslt=index-document.xslt/
map:transform type=xslt src=document-to-web.xslt/
map:serialize type=html/
/map:match
The idea is that the xslt generator can be used with any source. For
this to be efficient with Momento we must organize so that the XSLT
processor can access momento as a read-only DOM. This will not happen
today in Cocoon. So what I describe is how to extend the involved
mechanisms in Cocoon so that Momento get DOM as input.
This is done by creating a new interface, let us call it
ReadOnlyDOMizable to avoid confusion ;) so that we can check if a
source, (e.g. the Momento source), can return a DOM. We also need to
extend the URIResolver in the XSLT processor implementation so that it
returns a DOMSource if the input source implements ReadOnlyDOMizable,
SAXSource, if the input source implements XMLizable and StreamSource
othewise. That is all.
The implementation of the URIResolver that is used is
Momento and Cocoon [was Re: Jisp 3.0 moved to GPL licence]
[changing subject...] Reinhard Poetz wrote: From: Alan * Geoff Howard [EMAIL PROTECTED] [2004-02-22 18:47]: Alan wrote: * Upayavira [EMAIL PROTECTED] [2004-02-22 07:58]: I tend to think that Momento isn't suited to this need. However, as an XML data repository, it seems very interesting. I've got a better idea of how Jisp is used in Cocoon from reading all the discussion after my post. I suggested Momento because someone suggested Xindice which led me to believe Jisp handled an XML persistence task. Might not be the best bet, no. Still, I think finding a way to use momento to reduce memory overhead in working with large xml datasets has great potential. No one really knows how great, but a demo/sample using it would be a start... (hint hint :) ) Working on it. As noted, I have JAXP implemented and SAX interface to XUpdate. I have APIs. I am going to start working on services next. A Cocoon generator that takes a Momento data source and an XSLT transform would be a start. I'm not sure how to get information into Momento via Cocoon. I'm thinking about some sort of Woody binding, but that goes beyond my current understanding of Cocoon. speaking without following this thread closly: What about implementing a Momento source? Yup. Alan, take a look at the XMLDBSource and XMLDBSourceFactory. I think you'll find them reasonably similar to what you might want to do (in src/blocks/xmldb/java/org/apache/cocoon/components/source/impl) If you implemented a MomentoSource, and made it implement ModifiableSource, then you would be able to read/write from within Cocoon. With this, you would be able to use Woody's binding functionality to bind forms directly to Momento data. You could also do something like the XMLDBTransformer to allow updates (src/blocks/xmldb/java/org/apache/cocoon/transformation/XMLDBTransformer.java). [NB. with an XML:DB interface to Momento, you wouldn't need to do anything to interface to Cocoon]. Hope this helps. Regards, Upayavira
RE: Momento and Cocoon [was Re: Jisp 3.0 moved to GPL licence]
From: Upayavira speaking without following this thread closly: What about implementing a Momento source? Yup. Alan, take a look at the XMLDBSource and XMLDBSourceFactory. I think you'll find them reasonably similar to what you might want to do (in src/blocks/xmldb/java/org/apache/cocoon/components/source/impl) If you implemented a MomentoSource, and made it implement ModifiableSource, then you would be able to read/write from within Cocoon. With this, you would be able to use Woody's binding functionality to bind forms directly to Momento data. You could also do something like the XMLDBTransformer to allow updates (src/blocks/xmldb/java/org/apache/cocoon/transformation/XMLDBT ransformer.java). [NB. with an XML:DB interface to Momento, you wouldn't need to do anything to interface to Cocoon]. Hope this helps. Thanks, this is exactly what I was thinking of! Best, Reinhard
Re: Momento and Cocoon [was Re: Jisp 3.0 moved to GPL licence]
Upayavira wrote:
Reinhard Poetz wrote:
From: Alan
Working on it. As noted, I have JAXP implemented and SAX interface
to XUpdate. I have APIs. I am going to start working on services
next.
A Cocoon generator that takes a Momento data source and an XSLT
transform would be a start.
I'm not sure how to get information into Momento via Cocoon. I'm
thinking about some sort of Woody binding, but that goes beyond
my current understanding of Cocoon.
speaking without following this thread closly: What about implementing
a Momento source?
Yup. Alan, take a look at the XMLDBSource and XMLDBSourceFactory. I
think you'll find them reasonably similar to what you might want to do
(in src/blocks/xmldb/java/org/apache/cocoon/components/source/impl)
If you implemented a MomentoSource, and made it implement
ModifiableSource, then you would be able to read/write from within
Cocoon. With this, you would be able to use Woody's binding
functionality to bind forms directly to Momento data.
You could also do something like the XMLDBTransformer to allow updates
(src/blocks/xmldb/java/org/apache/cocoon/transformation/XMLDBTransformer.java).
[NB. with an XML:DB interface to Momento, you wouldn't need to do
anything to interface to Cocoon].
Hope this helps.
Regards, Upayavira
I agree with the above suggestions and would like to provide some more
technical details.
Pseudo protocol
===
In Cocoon (or actually Avalon Excalibur), we have a generalization of
protocols, java.net.URL, called pseudo protocol
org.apache.excalibur.source.Source, there are also various extensions of
Source like ModifiableSource, TraversableSource among others. Pseudo
protocols are an excelent way of separating the location of data with
what to do with it. If you package a data source as a pseudo protocol
you can access it by using its URL, e.g.
momento://dbpath/collection#xpath(foo/bar), through Cocoons source
resolver. This makes it possible to use sources for ala src attributes
in the sitemap, the document function in XSLT and XQuery, hrefs in the
[X|C]IncludeTransformer, in the SourceWritingTransformer and within
flowscripts.
A MomentoSource would thus give a lot of flexibility in using Momento in
Cocoon. Especially if it allows using XPath(2.0) in the URLs and if it
is a modifyable source.
XSLT
A MomentoSource would also give a good way to use Momento together with
XSLT and XQuery in Cocoon. Here we need to extend the ordinary use of
sources somewhat, let me explain:
The Source interface provides a getInputStream method, in Cocoon some
Sources implements org.apache.excalibur.xml.sax.XMLizable that provides
a toSAX method as well. SAX or Streams are probably not the most
efficient way to communicate with an XML db, so to make the pseudo
protocol idea usable together with Momento, we should provide a way to
get a DOM structure from a pseudo protocol. This could be done by
introducing a new interface:
interface DOMizable {
org.w3c.domNode getNode();
}
or something similar. If the MomentoSource implements DOMizable, we have
direct access to nodes in the XML db.
Now we are prepared to connect Momento to XSLT. In Cocoon we can use
Saxon through the org.apache.cocoon.transformation.TraxTransformer, you
just need to change cocoon.xconf a little bit to use Saxon instead of
Xalan. There is also a TraxGenerator in the scratchpad that could be
used with some small modifications.
I would guess that Momento mainly would be accessed through the document
function in XSLT and XQuery. Saxon use JAXP 1.1 as external API to the
transformerand the URLs in the document functions are resolved by using
an implementation of javax.xml.transform.URIResolver that is provided by
the TraxTransformer.
The implementation of the URIResolver that is used is
org.apache.excalibur.xml.xslt.XSLTProcessorImpl in its current
incarnation it uses the exclaibur source resolver to get the source and
then it returns a javax.xml.transform.stream.StreamSource. For use with
Momento we need an implemetation of URIResolver that checks if the the
source is DOMIzable and in that case returns a
javax.xml.transform.dom.DOMSource instead. This can be done by extending
the excalibur XSLTProcessorImpl and change the XSLTProcessor in
cocoon.xconf.
XQuery
==
XQuery in Saxon use a propertary api, (there are no standard in this
area yet). So we need a specialized SaxonXQueryGenerator. Saxon use the
JAXP URIResolver for XQuery also, so the above described mechanisms can
be used here as well. Unfortionatly Saxon is MPL 1.0 that is not
compatible with ASL, so we cannot have Saxon as a part of Cocoon :(
--- o0o ---
Sorry for all the technical details ;)
As you can see, for reading from Momento, the only Momento specific code
is in the MomentoSource, everything else is using DOM, JAXP and Cocoon
APIs. Therefore the proposed mechanisms would give an efficient way of
