The logic terms are specified in an ontology that provides a formal description of the components and their relationships that make up a process.
In the manufacturing domain, PSL's objective is to serve as a common representation for integrating several process-related applications throughout the manufacturing process life cycle.
[1] The foundation of the ontology of PSL is a set of primitive concepts (object, activity, activity_occurrence, timepoint), constants (inf+, inf-), functions (beginof, endof), and relations (occurrence_of, participates_in, between, before, exists_at, is_occurring_at).
[2] The ontology uses the Common Logic Interchange Format (CLIF) to represent the concepts, constants, functions, and relations.
[3] This ontology provides a vocabulary of classes and relations for concepts at the ground level of event-instances, object-instances, and timepoints.