Rainer Schiekofer

Zusammenfassung

The communication protocol OPC UA is one of the most important IIoT enablers within the automation domain. OPC UA not only aims to provide interoperability on the transport layer, but also interoperability of the semantic layer shall be addressed based on so-called Companion Specifications. However, the lack of OPC UA formal semantics makes automatic validation of OPC UA data models impossible. Another drawback is the shortage of available tools for OPC UA, such as an implementation of the query engine for the specified OPC UA query language. In this paper we provide a formal translation of OPC UA models to the Semantic Web standard OWL, thus making OPC UA implicit semantics, that is described in the documentation, explicit, by means of OWL axioms. Moreover, we outline how this mapping can be used to offer validation and querying of OPC UA data models based on already existing Semantic Web technology.

Zusammenfassung

In the automation domain, OPC UA can be considered one of the most important communication protocols for IIoT applications. According to a study of McKinsey the potential economic impact of the IoT within factories may reach up to 3,7 Trillion Dollar by 2025. To unlock this potential it is very important to bridge the interoperability gap. Since V1.04 OPC UA also supports session-less clients and therefore allows the development of RESTful clients which can be used to address the cross-domain interoperability issue. However, currently, RESTful clients cannot use Subscriptions, because the corresponding Service Sets are not supported for session-less clients. In this paper, we will present how Subscriptions can be introduced for session-less clients. Furthermore, we outline how Group-Subscriptions can be introduced for session-less as well as session-based clients. Finally, our evaluation shows that Group-Subscriptions significantly outperform standard Subscriptions if the Subscription can be shared by several clients.

Zusammenfassung

OPC UA is one of the most important communication protocols for IIoT applications in the automation domain. One important requirement for Industry 4.0 scenarios is standardized semantics, which is introduced into OPC UA through Companion Specifications. Nevertheless, OPC UA still lacks a comfortable interface for accessing these huge graphs, especially on the edge- and cloud-layer. Of course, there is a query language specified for OPC UA. However, to the best of our knowledge, there is no publicly available implementation. In this paper, we will present how SPARQL can be used to query OPC UA graphs natively and also will present rules to transform OPC UA queries into SPARQL queries. Furthermore, we will highlight some issues of OPC UA Query and how they can be bypassed by native SPARQL. Finally, we were able to correctly execute all nine example queries of OPC UA Part 4 Annex B (complex examples) with both approaches.

Zusammenfassung

OPC UA is one of the most important communication protocols for Industry 4.0 applications in the automation domain. However, to really reach the status of an Internet-of-Things protocol, OPC UA also has to give some answers to upcoming cross-domain questions. Only if OPC UA is able to bridge the gap between several different domains, it will be accepted as real Internet-of-Things protocol and therefore supported even better by the APIs of the big IT players. One technology which already interconnects nearly every domain is the REST architecture. A lot of research already focused on the combination of these two technologies. However, in this paper we will show the first approach which covers all OPC UA requirements and therefore enables also use cases like server reconfiguration. We will also give some insights into our concept, which was contributed to the OPC UA specification as part of the V1.04 release.