Elektrotechnik & Informationstechnik, Institut für Automatisierungstechnik, Professur Prozessleittechnik Linked Data Adapter for OPC UA Integrating Industrial Middleware in Linked Data Collaboration Networks Markus Graube, Jan Hladik, Leon Urbas ETFA 2016
Agenda Motivation Linked Data Transient data in LD Concept Accesing transient data in LD Mapping between OPC UA and Linked Data Implementation Conclusion 08.09.2016 Linked Data Adapter for OPC UA 2
Linked Data as Information Backend Semantic Information model Open-World-Assumption Extensibility References as first class items Light-weight approach Model as you use / Pay as you go Decentral Architecture cross-domain links 08.09.2016 Linked Data Adapter for OPC UA 3
Linked Data Technologies RDF URIs HTTP <Subject> <Predicate> <Object>. unique & dereferencable internet standard for access Ontologies General: RDFS, OWL Domain specific same model as for instances SPARQL graph based query language for RDF 08.09.2016 Linked Data Adapter for OPC UA 4
ComVantage Linked Data Architecture (Ziegler et. al, ETFA 2012) 08.09.2016 Linked Data Adapter for OPC UA 5
Hierarchy Aggregation Variables Functions Classes Methods Inheritance Derefencable References Federated Queries Information models for transient data (Mahnke et. al, 2011, Automation) Already established middlewares OPC UA and Substation Automation (IEC 61850) already provide an established and mature information model LD provides some additional modeling concepts, however focussed on static data IEC 61850 X X X - (x) - - - - OPC UA X X X X X X X - - Linked Data X X X X X (x) X X X 08.09.2016 Linked Data Adapter for OPC UA 6
Comparison OPC UA and Linked Data OPC UA Origin Automation Industry Characteristics Unique reference via server URL and node ID Advantages Performant dynamic data exchange Realtime capabilities in development Subscriptions Alarms Integration in most automation systems (in the future) Linked Data Origin Semantic Web (IT) Characteristics Unique reference via HTTP URI Advantages Tailored for providing heterogenous decentral information spaces Revisioning mechanisms Large community with big public available data sets Comprehensive tool support Using established internet standards Commonalities Semantic information model Graph based Isomorphic mapping possible Service oriented adapter between both worlds 08.09.2016 7 Linked Data Adapter for OPC UA
Linked Data OPC UA Adapter Approach OPC UA adapter for accessing transient data in LD Challenges 1. Model transient data in Linked Data 2. Providing a mechanism for accessing this information 08.09.2016 Linked Data Adapter for OPC UA 8
Challenge 1: VOPR vocabulary Resulting process data needs to be modelled by a specific vocabulary Several ontologies are available describing physical quantities and units (e.g. QUDT) http://www.qudt.org describing statistical datasets (RDF data Cube vocabulary) http://www.w3.org/tr/vocab-data-cube/ Combination into Vocabulary Of Processvariable Representation (VOPR), which is used to deliver information from the Linked Data adapter and link to the specific REST resources. 08.09.2016 Linked Data Adapter for OPC UA 9
Challenge 2: Linked Data Adapter - Access to transient data Cyclic polling and storing in triplestore Simple approach Performance limits Seperation sensors and actuators are semantically described in the LD cloud including information about the access method Direct access to the data via a dedicated Linked Data adapter on demand 08.09.2016 Linked Data Adapter for OPC UA 10
Linked Data Adapter: Live Data Access Application Retrieving of static semantic information from LD cloud hierarchic plant structure Sensor properties Method for accessing sensor data HTTP request LD Adapter Transformation of HTTP requests into middleware calls Read sensors or acuators Write actuators Result Recent value in RDF serialisation (e.g. Turtle) 08.09.2016 Linked Data Adapter for OPC UA 11
Linked Data vs. REST services (Page, De Roure, Martinez, 2011) REST Representational State Transfer Paradigm for web applications Compatible to Linked Data Resources Identification via URIs Preference of HTTP Links Semantic information independant from resource identifier adaptability 08.09.2016 Linked Data Adapter for OPC UA 12
Mapping OPC UA & LD OPC UA NodeId (Namespace + Type + Value) ns=2;i=84 Linked Data HTTP URI Direct Mapping possible http://<server>/<path>/ns/<namespace>/<type>/<value> Alternative http://<server>/<path>/?ns=<namespace>&<type>=<value> Examples http://eatld.et.tu-dresden.de/opcua2ld/ns/2/i/84 namespace: 2 Identifier: i=84 http://eatld.et.tu-dresden.de/opcua2ld/ns/3/s/pumpp001 Namespace: 3 Identifier: s=pumpp001 08.09.2016 Linked Data Adapter for OPC UA 13
OPC UA Services as REST requests (1/2) GET request Browse Service?browse ReadAttribte Service?attribute HistoryRead Service?start?end POST request WriteAttribute Service New information in HTTP body CallMethod Service PUT request methodid and parameters in HTTP body addnode Service Information in HTTP body DELETE request deletenode Service 08.09.2016 Linked Data Adapter for OPC UA 14
OPC UA Services as REST requests (2/2) Low Level OPC UA services directly handled by adapter SecureChannel, Session and Discovery Service sets Unsupported OPC UA services MonitoredItem Service Set Subscription Service Set HistoryUpdate BrowseNext RegisterNode/UnregisterNode 08.09.2016 Linked Data Adapter for OPC UA 15
Serialisation (1/2) Browse GET http://eatld.et.tudresden.de/opcua2ld/ns/2/i/23 mw:ns/2/i/23 a opcua:node; opcua:browsename Subplant 1 ; opcua:hastypedefinition mw:ns/2/i/61; opcua:organizes mw:ns/2/i/25, mw/ns/2/s/pumpa; mw:ns/2/s/isconnectedto mw:ns/2/i/24. Reading values GET http://eatld.et.tudresden.de/opcua2ld/ns/2/is/pum pa?attribute=value [] a vopr:value ; vopr:value 23.0; vopr:attime "2016-04- 12T10:50:28Z ; vopr:providedby mw:ns/2/s/pumpa. 08.09.2016 Linked Data Adapter for OPC UA 16
Serialisation (2/2) Historical Data GET http://eatld.et.tu-dresden.de/opcua2ld/ns/2/s/pumpa?attribute=value&start=2016-04-09t154045&end=2016-09-04t154445 [] a vopr:historyslice ; vopr:startat "2016-04-09T15:40:45.177 ; vopr:endat "2016-04-09T15:44:45.177 ; vopr:hashistory[ ]; a rdf:seq ; rdf:_1 [ a vopr:value ; vopr:attime "2016-04-09T15:43:50.375 ; vopr:value "67.0"] ; rdf:_2 [ a vopr:value ; vopr:attime "2016-04-09T15:43:49.375"; vopr:value "66.0"]; vopr:providedby mw:ns/2/s/pumpa. 08.09.2016 Linked Data Adapter for OPC UA 17
Prototypical Implementation Java Application Prosys OPC UA SDK Jersey Web Service Proof-of-concept Browse, Read, Write, CallMethod 08.09.2016 Linked Data Adapter for OPC UA 18
Conclusion Discussion Integration of OPC UA and LD possible Advantages from both worlds Prototypical implementation shows feasibility Back link from OPC UA to LD necessary Next Steps Reimplementation and performance evaluation Better support of web applications JSON-LD as serialisation Concept for integrating Query Service set into REST service SPARQL-Bridge 08.09.2016 Linked Data Adapter for OPC UA 19
Thank you for your attention! For question, please contact: markus.graube@tu-dresden.de Prof. Dr. habil. Leon Urbas Technische Universität Dresden Fakultät Elektrotechnik und Informationstechnik Institut für Automatisierungstechnik Tel.: +49 351 463-34604 Fax: +49 351 463-39681 Besucheradresse: Barkhausen-Bau Georg-Schumann-Str. 11 01187 Dresden Postanschrift (Briefe): Technische Universität Dresden Fakultät Elektrotechnik und Informationstechnik Institut für Automatisierungstechnik 01062 Dresden