HTN Planning with Preferences

Aims to extend SHOP2 with support for "temporal preferences." Examples from the paper is that the lights are eventually turned off, and that some actor never holds an object tagged as "explosive."

Metric function: defines the fitness or badness of a plan. Combines is-validated predicates and combines them with user defined weights to set how good or bad a plan appears to be.

is-validated gives you the number of critic functions of a given family reported an issue. For example the number of trucks which do not have fuel.

Preferences are stated with temporal logic functions: something never happens, eventually happens, something is true at the beginning or ending of a plan.

Preprocessing by removing invalid options; if a preference says to never allow a given symbol, then remove proposals that have the symbol from the list of possibilities.

Planning performs a tree search where compound problems are replaced using methods. The plan is rated for badness using the metric function. Tree exploration follows the most promising leads through the tree until a plan is completed.