[rules-dev] Drools XML Language and Tools Development

[Mark Proctor]

Rule base systems typically had simple languages. Data structures where 
either list or frames, the number of constructs are very limited. 
Complex expressions, such as nested accessors did not exist - like with 
Drools 3.0. That made it very easy to support a 1 to 1 mapping in xml.

Around Drools 4 out langauge become more expression, we started to allow 
complex expresisons inside of patterns. In Drools 5.3 that is even more 
so. It quickly became obvious that xml representation fo drools would 
also need a representation for java expressions, this was going to be a 
lot of work - especially as we would probably have to change a lot of 
the existing xml.

It seems very few people are using the xml, certainly no one seemed to 
care about it. Xml parsers and schemas is something that every java 
developer can do, but no one has come forward maintain this. So we've 
let it die.

I'm not sure I'd want to resurrect it, for a one of piece of work.  It's 
likely the maintainenance of this would soon fall back on the core 
developers.

I think  I'd rather see xml efforts around RuleML and/or RIF. So imho if 
you want to do anything, do it around those. The downside is that 
representing our more powerful constructs like sliding time windows may 
not be possible in those languages, and you would need to define extensions.

Mark
On 10/01/2012 22:08, Justin Holmes wrote:
> Hello Devs,
> My name is Justin Holmes and I'm a Middleware Consultant for Red Hat. 
> I'm currently staffed on an engagement that provides a very 
> interesting use case for Drools. In particular, our teams 
> currently believes that the Drools XML Language would be the best 
> possible solution for one of our problem. We are aware that the Drools 
> XML language has not been developed for sometime and is considered 
> deprecated. Additionally, the application will need to support 
> Drools CEP functionality in the near future. Before we begin crafting 
> a custom solution, we would like to ask:
> 1) Is the XML language truly the best option for our use case?
> 2) If it is the best option, how do we begin developing the XML 
> language and tools (XMLPackageReader) to fully support at least BRMS 5.2?
> *Context: *
> Client is using Drool 5.1.1 and we are migrating to BRMS 5.2. There 
> are two independent workflows of interest:
> *1) Rule Authoring and DRL generation*: The rule assets and metadata 
> are kept in a custom format (both relational DB and XML) in order to 
> decouple it from the runtime. Thus, the client wrote their own GUI and 
> content manager instead of using Guvnor. The custom GUI allows 
> business users to author 3 types of content, as well as rules for 
> these types of content, using a guided-rule editor with domain 
> specific language. The following steps occur when a user wants 
> to produce a new version of a rule:
> i) GUI saves LHS rule logic in an XML database using MathML 
> (http://www.w3.org/Math/), and then saves everything else in a 
> relational database.
> ii) iBATIS pulls down the corresponding database and XML entries and 
> populates POJOs. There is 1 class definition per content type.
> iii) Cumbersome application code translates POJOs into 
> Drools PackageDescr (~5000 lines of code, not using fluent API). This 
> step produces a very strange and convoluted representation of the LHS 
> of each RuleDescr. It works with DrlDumper 5.1.1 but does not work 
> properly with the BRMS 5.2 version of DrlDumper (MVEL Template). This 
> is the source of our problem.
> iv) PackageDescr is dumped into a valid DRL string with Drools DrlDumper
> v) Custom content manager does some versioning and then stores DRL in 
> an XML database
>
> *2) Deployment and Runtime: *App is deployed daily and will have 
> dozens of runtimes during that 24 span. When deployed, it pulls all 
> rules from the database and builds several KnowledgePackages, which 
> are cached, and then used throughout the day.
>
> *Proposed Solution:*
>
> Because the app code that performs step iii) is so convoluted and 
> will need to be modified in order to support CEP, we want to pursue a 
> more maintainable solution to provide the translation and abandon the 
> mess that is already in the application. We feel that rewriting this 
> code with the fluent API is just as dangerous as the present code. 
> Additionally, the rules are far too variable to use Rule templating.
>
> So, we propose to translate the client's custom rule assets and 
> metadata into the Drools XML Language, parse the XML and dump out 
> DRLs. We will likely need to use the existing intermediate POJOs for 
> this. The most difficult piece in the puzzle by far is translating the 
> LHS of rules, and of course this is the part that is broken currently 
> in our system. We believe that it should be MUCH easier to translate 
> the well formatted MathML representation of the LHS to the Drools XML 
> schema using XSLT, than to translate it to PackageDescrs with Java 
> code. There are also the additional benefits of validation and 
> portability presented by XML. The downside here is that the XML 
> language and tools are out of date, so we would need to develop these 
> solutions first.
>
> Both consultants on this project have been interested in contributing 
> to the Drools project and we feel this could be the perfect entry 
> point. We realize this is a complicated question and presenting it 
> over email is limiting, so please feel free to contact me by phone.
>
> Thank you,
>
> ---
> Justin Holmes
> Red Hat Consulting
> 410.599.8432 : mobile
> http://www.redhat.com/consulting/
>
>
>
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