The DRL is an alternative way of calculating the score than the ProjectJobSchedulingIncrementalScoreCalculator. It's slower, but far more readable and maintainable.

1) Finish the file projectJobSchedulingScoreRules.drl so it has all required score constraints of projectjobscheduling.
https://github.com/droolsjbpm/optaplanner/blob/master/optaplanner-examples/src/main/resources/org/optaplanner/examples/projectjobscheduling/solver/projectJobSchedulingScoreRules.drl

2) For a list of those score constraints, read the documentation
http://docs.jboss.org/drools/release/latest/optaplanner-docs/html_single/index.html#projectJobScheduling
and look at ProjectJobSchedulingIncrementalScoreCalculator.java (which is much more complex because it actually does the delta's itself)
In the docs, read up about "incremental score calculation":
http://docs.jboss.org/drools/release/latest/optaplanner-docs/html_single/index.html#incrementalScoreCalculation
and
http://docs.jboss.org/drools/release/latest/optaplanner-docs/html_single/index.html#d0e4210

3) Use projectJobSchedulingSolverConfig.xml to verify if the DRL works properly by commenting out "<incrementalScoreCalculatorClass>" and commenting in "<scoreDrl>". Use "<assertionScoreDirectorFactory>" (see docs) to validate that it consistently gives the same score as ProjectJobSchedulingIncrementalScoreCalculator.
Note: if you find a bug in ProjectJobSchedulingIncrementalScoreCalculator, let us know