A comment led me to visit https://hudson.jboss.org/hudson/job/drools/lastSuccessfulBuild/artifact/trunk/target/docs/drools-solver/html_single/index.html. Section 188.8.131.52 has an interesting statement about the Simplex method:
If the word Simplex was missing I would not recognize this is about the Simplex method. One big equation? (No word about not being suited to handle discrete variables).
Simplex turns all constraints and data into a big equation, which it transmutes into a mathematical function without local optima. It then finds an optimal solution to the planning problem by finding an optima of that mathematical function.
The branch&bound section is also interesting. No mention about the unique feature that it provides bounds and hence an indication of the quality of the solution.