Dredd Rule Engine

Dredd was created to be a simple way to detach application business logic in order to create a decision tree model best for visualize and perhaps easy to understand and maintain.

Should I use a Rules Engine?

• A rules engine is all about providing an alternative computational model. Instead of the usual imperative model, commands in sequence with conditionals and loops, it provides a list of production rules. Each rule has a condition and an action - simplistically you can think of it as a bunch of if-then statements.

• As in many places, testing is often undervalued here, but implicit behavior makes testing more important - and it needs to be done with production data.

• One common discussion concerns encapsulating business logic (i.e., rules) within objects or services. Services make sense for decisions and compliance that are orchestrated by the business process. If a requirement, regulation, policy or rule spans many classes in the model and many tasks within the process, externalized rules are strongly indicated.

Heuristics to use rule engine

• As the number of criteria increases
• As the set of criteria becomes more dynamic
• As the criteria become more complex

Why I do not use Drools ?

• This project was born in a project where payload size of jar, memory consumption , cpu utilization and easy maintenance was a rule of thumb , thus Drools was a huge and overweight solution for our "simple" solution
• There is a lot of work in order to make Drools run in Android , done by good people at community, but honestly regarding all the weird workarounds I not felt comfortable to go with those "stitched" tires.
• A lot of dependencies that we ain't gonna need and will just augment the size of final artifact .

And about good principles of OOP?

• We just follow the SOLID principles
• Try to avoid over engineering , I mean, create a lot of classes, interfaces just for sake of architecture.
• We need to maintain the components easy to understand, decoupled and tolerate to changes.

Reference

• InfoQ article
• Martin Fowler article about Rule Engines
• Rules Engine on mobile platform : Getting Rule engine to work on Mobile Platform
• SOLID revisited

License

Copyright 2015 Amsterda Technology, Inc.  Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License. You may obtain a copy of the License at
  http://www.apache.org/licenses/LICENSE-2.0  Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.