Semantic data interoperability has attracted a lot of attention in recent years, with ontologies being one of the major tools to accomplish the goal of seamless data and application integration in manufacturing, industry and supply chains. Among the most challenging issues are semantic relations between manufacturing plans and their realization in actual production. This paper provides a model based on the IOF approach to the subject. The initial discussion is devoted to the semantic modelling of intentions, desires, plans and actions, from which we propose the specification/process approach to modelling plans and their realizations. The developed ontological model of plans includes relations between specifications and future occurrences; models of sequences, hierarchy, and alternatives; and conformance of executed processes to their planned counterparts as given by specifications. The model is illustrated by several small examples implemented in OWL language.