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xpl doubts (and suggestions).

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SateeshK

xpl doubts (and suggestions).

Hi,

I have a few questions regarding xpl.
I am trying to figure out how best to structure xpl (for performance and reusability).

What "flows" between the processors? Does xml get converted when an output is read or once xml enters a pipeline, does it remain in object (java) graphs until it's serialized?

How does the xpl engine pick which processor to start the execution with? is it the last one listed?
In the command line or in the xpl itself is there a way to specify that execution start with a certain processor?

Is there any future enhancement to visually build xpl? Something similar to Clover, Ab Initio, Yahoo pipes, which follow similar methodology where the core engines treat blocks of code (with input & output ports) as part of a graph that can be executed.
I don't know if I am conveying the right thought here, but I am thinking, if the xpl engine can be directed to:
1. Pick a certain processor to execute (there will be always the default behaviour).
2. Allow xpl to indicate if the i/o should be local or remote.
a) local execution => same behaviour as now.
b) remote execution => use xmlrpc to communicate with clustered instances of orbeon.
3. have a visual builder to enable:
a) have named blocks of xpl.
b). show oxf processors and above named blocks in a pallet and allow a bigger block to be build.

Thanks,
- Sateesh.

Erik Bruchez

Re: xpl doubts (and suggestions).

Administrator

> What "flows" between the processors? Does xml get converted when an
> output
> is read or once xml enters a pipeline, does it remain in object (java)
> graphs until it's serialized?

It's SAX events.

> How does the xpl engine pick which processor to start the execution
> with?
> is it the last one listed?

This may help:

http://www.w3.org/Submission/xpl/#processing-model

It's based on lazy evaluation, in other terms, you start with the
output, and then inputs are read when needed.

Processor without outputs are read first within a block.

> In the command line or in the xpl itself is there a way to specify
> that
> execution start with a certain processor?

This is not possible at the moment. The processing model does not
allow it.

> Is there any future enhancement to visually build xpl? Something
> similar
> to Clover, Ab Initio, Yahoo pipes, which follow similar methodology
> where
> the core engines treat blocks of code (with input & output ports) as
> part of
> a graph that can be executed.

We don't plan to build a visual tool for creating pipelines. This
would certainly nice, and while XPL is very powerful and we use it
daily, we have very limited resources to dedicate to it.

> I don't know if I am conveying the right thought here, but I am
> thinking,
> if the xpl engine can be directed to:
> 1. Pick a certain processor to execute (there will be always the
> default
> behaviour).
> 2. Allow xpl to indicate if the i/o should be local or remote.
> a) local execution => same behaviour as now.
> b) remote execution => use xmlrpc to communicate with clustered
> instances of orbeon.
> 3. have a visual builder to enable:
> a) have named blocks of xpl.
> b). show oxf processors and above named blocks in a pallet and
> allow a
> bigger block to be build.

Those are good suggestions. Just be aware that we are unlikely to have
time to work on them at Orbeon. But Orbeon Forms is open source so
anybody can do so!

You may also want to look at XProc, XPL's successor, which it would be
great to implement in Orbeon as well, perhaps on top of XPL at first:

http://www.w3.org/TR/xproc/

-Erik

--
Orbeon Forms - Web Forms for the Enterprise Done the Right Way
http://www.orbeon.com/

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SateeshK

Re: xpl doubts (and suggestions).

Thanks for the feed back.

- Sateesh.

Erik Bruchez wrote

> What "flows" between the processors? Does xml get converted when an
> output
> is read or once xml enters a pipeline, does it remain in object (java)
> graphs until it's serialized?

It's SAX events.

> How does the xpl engine pick which processor to start the execution
> with?
> is it the last one listed?

This may help:

http://www.w3.org/Submission/xpl/#processing-model

It's based on lazy evaluation, in other terms, you start with the
output, and then inputs are read when needed.

Processor without outputs are read first within a block.

> In the command line or in the xpl itself is there a way to specify
> that
> execution start with a certain processor?

This is not possible at the moment. The processing model does not
allow it.

> Is there any future enhancement to visually build xpl? Something
> similar
> to Clover, Ab Initio, Yahoo pipes, which follow similar methodology
> where
> the core engines treat blocks of code (with input & output ports) as
> part of
> a graph that can be executed.

We don't plan to build a visual tool for creating pipelines. This
would certainly nice, and while XPL is very powerful and we use it
daily, we have very limited resources to dedicate to it.

> I don't know if I am conveying the right thought here, but I am
> thinking,
> if the xpl engine can be directed to:
> 1. Pick a certain processor to execute (there will be always the
> default
> behaviour).
> 2. Allow xpl to indicate if the i/o should be local or remote.
> a) local execution => same behaviour as now.
> b) remote execution => use xmlrpc to communicate with clustered
> instances of orbeon.
> 3. have a visual builder to enable:
> a) have named blocks of xpl.
> b). show oxf processors and above named blocks in a pallet and
> allow a
> bigger block to be build.

Those are good suggestions. Just be aware that we are unlikely to have
time to work on them at Orbeon. But Orbeon Forms is open source so
anybody can do so!

You may also want to look at XProc, XPL's successor, which it would be
great to implement in Orbeon as well, perhaps on top of XPL at first:

http://www.w3.org/TR/xproc/

-Erik

--
Orbeon Forms - Web Forms for the Enterprise Done the Right Way
http://www.orbeon.com/

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