[rules-users] What should I insert into the working memory?

[Chris Selwyn]

Hi Wolfgang,

Thanks for the helpful response.

I do find myself using "contains" and "memberof" quite a lot depending 
on whether I am going "up" or "down" the tree structure. Is this a 
performance problem? Is it better to use "from"?
Thanks for the hint about adding the "parent" pointer in the child. I'll 
have to think about that one because the schema is actually shared with 
external trading partners.
I guess I could have an "external" version and and "internal" version 
but then I would have 2 versions to maintain and that is not very desirable.
As someone else has asked, I do actually make modifications to the model 
that I want to return to the client. So it is not read-only. That means 
I would then have to do a post-rule processing pass to null out the 
parent pointers (otherwise I would have cycles in the graph!) before 
returning the answer. Actually... @XmlTransient will probably have the 
desired effect.

(Thinks: I wonder whether it would be possible to write a JAXB plugin to 
do this stuff and make the generated classes more "rules-friendly")

Thanks also for the hint about the code injection plugin. I was not 
aware of that. I have just done some investigation into that and I find 
that the code-injection plugin is present  in my Glassfish server but is 
not named in the META-INF/services/com.sun.tools.xjc.Plugin file. So I'm 
not sure that I can use it without getting a separate installation of JAXB.

Chris


On 28/11/2010 13:12, Wolfgang Laun wrote:
> An XML schema just fitting your XML data will frequently not result in 
> a class
> hierarchy that's well suited for writing rules.
>
> One point deals with representing the parent-child relationship, 
> especially
> when there are multiple children of a kind, i.e., the parent class 
> contains a
> List<?>. You have this in XML the natural way; you lose it when you just
> insert parents and children.  If extending the XML schema is possible, you
> can add another element with minOccurs="0" to the Child complexType of
> type Parent and set the reference to the current parent when you walk the
> object tree. (You can erase the List<?> in the parent.) This avoids the
> frequent use of the "from" clause in conditions.
>
> You may also have to handle repeated occurrences of elements that are
> "equal" as objects but appear in full XML text; this is usually simple 
> to handle
> with a temporary Set, but you'll have to add hashCode and equals to the
> JAXB generated classes using the code injection plugin.
>
> Inserting just the root element is not advisable, as you are well 
> aware of.
>
> -W
>
>
>
> On 28 November 2010 12:38, Chris Selwyn <chris at selwyn-family.me.uk 
> <mailto:chris at selwyn-family.me.uk>> wrote:
>
>     I am working on a project that is using Drools to perform
>     validation of
>     hierarchical XML messages.
>
>     So I have passed the XSDs through JAXB and have a set of interrelated
>     Java objects.
>     One of these objects (naturally) represents the root of the
>     messages and
>     the others represent the intermediate and leaf nodes of the message.
>
>     My question is: Should I traverse the tree and insert each object into
>     the working memory or should I just insert the root object into the
>     working memory?
>
>     If I insert each object into the memory then I have a lot of
>     flexibility
>     about how I write my rules... I can start by focussing on the
>     particular
>     part of the message that I want to detect an error in.
>     However, I then have to perform a whole bunch of "joining" clauses to
>     correctly "connect up" to the other objects in the working memory.
>     (This is how I am doing it at the moment... I have a mechanism
>     that uses
>     the Java Introspector. It identifies by package name which parts
>     of the
>     data model get inserted into the WM)
>
>     On the other hand, I could just insert the root object into the
>     WM. This
>     means that I would have to write really complicated where clauses
>     on the
>     root object but very much simplifies the WM loading process.
>
>     All of the examples that I have seen have a very simple flat
>     (non-hierarchical) structure that don't really give a hint as to
>     what a
>     "best practice" might be.
>
>     Any suggestions/insights welcome :-)
>
>     Chris Selwyn
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