## 3 Semantic Service Description and Context-Based Orchestration
### Construction of Ontologies
#### 3.2.2 Selection of an Upper Ontology  
An upper ontology (or top-level ontology) contains very general knowledge across different domains. By referring to the general concepts of an upper ontology from more concrete concepts of domain and task ontologies, a semantic interoperability can be reached. That is why we investigated several existing upper ontologies, which could act as a common interoperability model for a structure of ontologies used for the semantic description of field device functionalities in assembly and handling. In addition to common upper ontologies like SUMO, Cyc or D  
Figure 1: Structure of modular ontologies for the semantic service description and context-based orchestration. ontologies that were developed with the objective of using them for applications in the manufacturing domain. There are three ontologies that appeared relevant for an in-depth investigation: MASON, ADACOR and AVILUS. MASON (Manufacturing's Semantics ONtology) [30] is aimed to provide a common semantic net in the manufacturing domain. Initially, it was used as knowledge base for an expert system used for cost estimation of the production of mechanical parts. This is the reason why MASON has a strongly product-centered point of view as well as detailed conceptualizations in the domain of metal working. The definition of the core concepts \"entity\", \"operation\" and \"resource\" is roughly oriented on the manufacturing decomposition proposed by [PERSON] and [PERSON] [31]. An examination of the OWL files revealed that the concepts provided by the ontology possess only weak to none axiomatic definition, leaving its meaning implicitly defined. However, the axiomatic definition of concepts is one of the main requirements of an upper ontology. The ADACOR-Ontology, which is based on the DOLCE upper ontology, was developed by [PERSON] and [PERSON] as a part of the ADACOR architecture [32]. The scope of the ADACOR-Ontology lies on manufacturing scheduling and control operations, thus providing a sophisticated conceptualization to model operations, process plans, work orders and production plans regarding customer orders and even production forecasts. Several studies have been published [33,34] which prove the axiomatic descriptions of the ontology's core concepts and show the successful application in the ADACOR architecture, where it has been used in a multi-agent manufacturing control system. Unfortunately, the files of the ontology are not openly available. Hence to be applied outside of the ADACOR project, the ontology has to be recreated with the information provided in the documentation. Due to the incompleteness of this published information, especially regarding the axiomatic definitions of most concepts, this is only possible to a limited degree and involves a not negligible amount of effort. The AVILUS-Ontology [35] is the result of a subproject of the AVILUS joint project, regarding product lifecycle management (PLM) as well as the management of production means with the goal of providing an application- and domain-independent model for information integration. Already existing neutral data formats have shown to be not expressive enough to serve this purpose, while the scope of special PLM formats is usually restricted to products only, excluding means of production. The Ontology is implemented in OWL DL and based on the design of the SUMO (Suggested Upper Merged Ontology) providing a great deal of interoperability. By using a modular design, consisting of a base ontology and several domain specific ontologies for mechanics, electrics, services _etc.,_ it ensures the adaptability to the user's needs. Because of its intended use for PLM as well as production means management, there is only one concept, called \"entity\", to represent both products and the means of production. Thus the ontology may take a product-centered point of view or a facility-centered point of view, depending which fits best for a given application.