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You can do this, set it up relationally, this is the "best practice"
way. This is what I told someone else:<br>
<br>
Nested lists and hashmaps aren't good things for rules. Instead what
you should do is break them apart and use a relational object to drive
this. Take at look at the conways game of life example in MR2. There
you'll see I have a grid of Cell objects, in the old version each Cell
had a HashSet of neighbour Cells - this setup doesn't work too well
with Rule Engines. Instead now I have a Neighbour class that acts as a
relation, so I assert all my Cells and then I assert a Neighbour class
for each neighbour pair I create. This creates a cross product, which
you can explioit to drive your application. Basically think
relationally, not nested structures, it's exactly the same problem if
you wanted to represent this information in a database.<br>
<br>
Mark<br>
<br>
Anirvan Majumdar wrote:
<blockquote
cite="mid:2cb74dd90705151037x30bf0013u8d0e944e41673cd@mail.gmail.com"
type="cite">Yeah,<br>
<br>
I'd second that. Mark's approach actually had me all dazed right from
the second line. I need to use Drools to accomplish a rather simple
task, however the suggestions made by Mark had me all lost. <br>
<br>
My requirement is that I have an <span style="font-style: italic;">input
</span>XML which my application should parse and output another XML.
The <span style="font-style: italic;">output </span>XML will have
tags and values capturing the required business model. The structure of
the <span style="font-style: italic;">input </span>XML is something
like this:<br>
<br>
<parent name="aaaaaaa"><br>
<child value="sdfsdfsdf"/><br>
<child value="sdfsdfsdf"/>
<br>
<child value="sdfsdfsdf"/><br>
<child value="sdfsdfsdf"/><br>
</parent><br>
<br>
Now the transformation of this input XML has to be done condition to
certain rules which our client will provide us. I thought Drools would
fit in very well. However after reading and acquiring a basic
understanding I came across this particular limitation.
<br>
<br>
My problem arises since, the input bean's <span
style="font-style: italic;">parent </span>tag can have varying number
of <span style="font-style: italic;">child </span>tags. As a
consequence, I can't define a single Bean class to capture this XML
data. I can capture the data in a HashMap, but then I can't access the <span
style="font-style: italic;">key-value </span>pairs from the "<span
style="font-style: italic;">when</span>" block of a rule.<br>
<br>
<span style="font-style: italic;">Arjun, </span>as you suggested,<br>
- can you tell me whether I can really utilize <span
style="font-style: italic;">DynaBeans </span>to meet my ends in this
particular case?<br>
- Can you also let me know a simple approach I can adopt? <br>
- also, if <span style="font-style: italic;">eval </span>can be used
in this case, can you pass across an example to show how to access say,
the <span style="font-style: italic;">key-values</span> from a HashMap
set in the asserted Bean object.<br>
<br>
Amongst the other Rule Engines, I still think that Drools fits in best.
A little help perhaps?<br>
<br>
Thanks a lot!
<br>
Anirvan<br>
<br>
<br>
<br>
<br>
<div><span class="gmail_quote">On 5/15/07, <b
class="gmail_sendername">Arjun Dhar</b> <<a moz-do-not-send="true"
href="mailto:dhar_ar@yahoo.com">dhar_ar@yahoo.com</a>> wrote:</span>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Mark
Proctor <mproctor <at> <a moz-do-not-send="true"
href="http://codehaus.org">codehaus.org</a>> writes:<br>
<br>
><br>
><br>
> You need to alter the parser and the Extractor api, you also need
to be<br>
> able to deal with ShadowFacts, where we need to know the previous
and
<br>
> current value.Further to that nested value should not change
without<br>
> notifying the parent fact in the network - i.e. correct network
state<br>
> must always been maintained. It's a complex area, we are looking
at a
<br>
> work around that allows this declarative language, but rewrites it
as<br>
> an eval - so you don't get the performance advantages - but it's a<br>
> quick work around for now.<br>
> Mark<br>
<br>
If what you want is the ability to extend the use of the class beyond
what it
<br>
was designed for (like a Dyna Bean, I think it is that!), then as a
work around<br>
you could use 'eval' over your object methods also, but this practice is<br>
discouraged for a few reasons.<br>
<br>
The other more sophisticated approach is already given by Mark!
<br>
<br>
regards,<br>
Arjun<br>
<br>
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