Doc Glossary

Glossary of common EUROPA terminology

EUROPA Glossary

• Active Token: A token which has been activated in the partial plan. See the token state transition diagram for further details.
• Base Domain: The maximal set of values a variable may take.
• Closed World Assumption: An assumption that no new objects can be inserted into the partial plan. This assumption is enforceable in EUROPA, and leads to stronger propagation. For more information, see Dynamic Objects.
• Compile Time Data: Those elements of a problem specification that are compiled prior to construction of a plan database, which remain static for the lifetime of a given plan database. Such data is typically considered the model. See the batch-solver process overview for further clarification.
• DDL: Domain Description Language. Developed by Nicola Muscettola for the HSTS planner.
• EUROPA: Extensible Reusable Remote Operations Planner. Refers to the planning technology platform consisting of a framework, a set of components, and a set of tools.
• Grounded Plan: a plan in which all variables have been specified to a singleton value.
• Plan Horizon: the temporal extent of the plan.
• Inactive Token: A token which has been created in the plan database, either explicitly through an invocation by an external client, or implicitly through execution of a model rule instance. However, such a token has not yet been activated, merged or rejected. See the token state transition diagram for further details.
• Interval Token: A token which has a duration of at least 1 time unit. All tokens on a class derived from Timeline are interval tokens.
• Lower limit: Minimum boundary of a resource where the assumption is to produce early and consume late.
• Master Token: An active token that has generated subgoals through rule instance execution.
• Merged Token: A token which has been merged with an active token in the partial plan. See the token state transition diagram for further details.
• Orphan Token: Any token that has been created by explicit request from a client external to the plan database. Such a token has no master.
• Parameter Constraint: A constraint declared in the body of a NDDL predicate declaration. It can only apply to the immediate context of the predicate (i.e. built-in varaibles and user-defined predicate parameters). Parameter constraints apply to inactive and active tokens.
• Partial Plan : a plan which is incomplete.
• Plan Database: an object responsible for management of all entities in a partial plan. It provides operations for legal restrictions and relaxations to the partial plan and co-ordinates automated reasoning services to propagate consequences of such operations according to the domain-model and rules of inference of EUROPA.
• Resource: A quantity which changes over time
• Rejected Token: A token which has been rejected from the partial plan. See the token state transition diagram for further details.
• Rule Instance: an instance of a model rule, scoped to a particular token and its subgoals.
• Run-time Data: those elements of a problem specification that are created or deleted during the lifetime of a plan database. See the batch-solver process overview for further clarification.
• Slave Token: Any token that has been created through rule instance execution.
• Solver: A problem solving agent which conducts refinements to a partial plan until it is completed, has exhausted all possibilities, or has exhausted all its allocated time. For more information see solvers.
• Specified Domain: indicates a subset of the base domain of a variable to which it has been specified by an external client.
• Transaction: the act of producing or consuming a resource
• Upper limit: Maximum bound of a resource where the assumption is to produce late and consume early.