[rules-users] Employee Shift Rostering: algorithm details

[HarrySimons]

Hi,

I'm new both to Drools Planner and to metaheuristic algorithms like Tabu
Search. Though I have done some preliminary reading on the Net on how this
algorithm 'generally' works -- including reading the 'plain-English'
portions of Chapter 8 of the 'Essentials of Metaheuristics' book -- it still
isn't perfectly clear to me how an actual implementation of the algorithm
would code the 'Tweak' / 'Next Move' function (other than via a random
combination of planning variables) in an application such as Employee Shift
Rostering with a very large search space and with multiple planning
variables.

On the page (http://www.jboss.org/drools/drools-planner.html) where Drools
Planner is compared side-by-side to other naive (greedy algorithms-based)
approachesfor various kinds of problems, could it be the case that the
algorithms used in Drools Planner were able to perfectly solve the
highlighted problems only because of the use of extremely small search
spaces / input datasets?! A wikipedia entry related to metaheuristic
algorithms says that not only is it possible that such an algorithm may not
give an optimal solution, it may not even give any solution at all(!!) due
to the algorithm reaching its timeout limit specified by the user. I'm
assuming it won't be possible to specify a timeout value in days or even
hours for any metaheuristics-based approach to a real-world problem of a
real-world scale.

Lastly, from looking at the pseudocode of Tabu Search, it *appears* that the
core, 'driver portion' of the algorithm may itself be not all that hard to
implement; it is rather the call-back portion of the algorithm (such as the
problem-specific Tweak / Next Move function, which the driver portion calls
back)  that may be hardest to implement. Given this, what would be the
advantages of using Drools Planner over a from-scratch, hand-coded version
of Tabu Search (other than its declarative, rule-based flexibility which a
hand-coded, from-scratch version may not want to implement due to its focus
on solving a specific planning problem vs. a whole slew of generic planning
problems requiring a generic piece of code such as Drools Planner)?

Would greatly appreciate if someone more knowlegeable than me could clarify
/ elaborate on the above getting-started questions of mine.

Regards,
/HS

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