Data Driven Rules Engine - Drools

Question

I have been evaluating Drools as a Rules Engine for use in our Business Web Application.

My use case is a Order Management Application.
And the rules are of

Answer 1

You asked me to give an answer to your question, given my answer to Data driven business rules. My answer to that question was that SQL is a bad solution to execute business rules stored in the database. The person who asked that question wanted to generate SQL expressions from their stored business rules, and I cautioned against doing that, because it would lead to problems in security, testability, performance, and maintenance.

I have not used Drools, but I gather from documentation that it includes Guvnor, a business rules manager that supports using an RDBMS as a repository for user-defined rules.

[Drools] Guvnor uses the JCR standard for storing assets such as rules. The default implementation is Apache Jackrabbit, http://jackrabbit.apache.org. This includes an out of the box storage engine/database, which you can use as is, or configure to use an existing RDBMS if needed. (http://docs.jboss.org/drools/release/5.2.0.Final/drools-guvnor-docs/html/chap-database_configuration.html)

Apache Jackrabbit is not an RDBMS, it is "a content repository is a hierarchical content store with support for structured and unstructured content, full text search, versioning, transactions, observation, and more." This seems like a more appropriate repository for Drools.

But Drools doesn't say it tries to use SQL to execute those business rules. It has a separate component, Drools Expert (Rules Engine) to do that.

Drools Expert is a declarative, rule based, coding environment. This allows you to focus on "what it is you want to do", and not the "how to do this". (http://www.jboss.org/drools/drools-expert.html)

SQL is also a declarative programming language, but it's designed to perform relational operations on table-structured data. A language to implement a rules engine has different goals, and can probably do things that SQL can't (and vice-versa).

So I would suggest if you use Drools, feel free to use an RDBMS as a repository as they document (use their JCR-compliant implementation of content repository, do not try to design your own). Then use their Drools Expert as a specialized language designed for executing rules.