Developing Distributed Semantic Systems
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This document discusses building distributed semantic systems. It describes defining an ontology to model the problem domain, formally describing the distributed system using Pi calculus, implementing RESTful semantic web services that expose ontology classes, and building client processes that interact with the services. An example exception logging system is used, with sensor processes monitoring exceptions, aggregator processes storing exceptions as resources, and a web client displaying exceptions. The Plaza framework facilitates developing the RESTful semantic web services and clients.
Developing Distributed Semantic Systems
- 1. Building Distributed Semantic Systems Antonio Garrote Hernández Monday, December 21, 2009
- 2. Definition • Distributed processes • Semantic meta data exposed as resources • Triple space operations • RESTful interface Monday, December 21, 2009
- 3. Different abstraction levels Monday, December 21, 2009
- 4. Monday, December 21, 2009
- 5. Sample application Monday, December 21, 2009
- 6. Exception logging system • Sensor processes monitoring generation of exceptions in different nodes and languages/platforms • Aggregator processes retrieving the exceptions and creating Exception resources • Exception RESTful semantic web service • Web client displaying generated exceptions Monday, December 21, 2009
- 7. Methodology Monday, December 21, 2009
- 8. 4 step process 1. Knowledge modeling 2. Formal description 3. Implementation of RESTful semantic services 4. Implementation of client processes Monday, December 21, 2009
- 9. 1.Knowledge modeling Monday, December 21, 2009
- 10. 1.Knowledge modeling • Building of an ontology for the problem domain • Ontology = TBox in Description Logics • Use of W3C’s standard languages: RDFS or OWL • Assistance of graphical tools like Protégé Monday, December 21, 2009
- 11. Sample application ontology level message createdAt Exception generated platform Node Language ipAddress domain dc:title formatPattern Monday, December 21, 2009
- 12. Developing the sample application ontology with Protégé Monday, December 21, 2009
- 13. Ontology(<http://semantic_rest/exceptions.owl> Declaration(Class(Exception)) SubClassOf(Exception owl:Thing) Declaration(Class(Node)) SubClassOf(Node owl:Thing) Declaration(Class(ProgrammingLanguage)) SubClassOf(ProgrammingLanguage owl:Thing) Declaration(ObjectProperty(platform)) ObjectPropertyDomain(platform Exception) ObjectPropertyRange(platform ProgrammingLanguage) Declaration(ObjectProperty(generatedIn)) ObjectPropertyDomain(generatedIn Exception) ObjectPropertyRange(generatedIn Node) Resulting ontology Declaration(DataProperty(level)) DataPropertyDomain(level Exception) using OWL DataPropertyRange(level rdfs:Literal) Declaration(DataProperty(ipAddress)) Functional Notation DataPropertyDomain(ipAddress Node) DataPropertyRange(ipAddress xsd:string) Declaration(DataProperty(formatPattern)) DataPropertyDomain(formatPattern Exception) DataPropertyRange(formatPattern xsd:string) Declaration(DataProperty(createdAt)) DataPropertyDomain(createdAt Exception) DataPropertyRange(createdAt xsd:dateTime) Declaration(DataProperty(content)) DataPropertyDomain(content Exception) DataPropertyRange(content xsd:string) Declaration(DataProperty(domain)) DataPropertyDomain(domain Node) DataPropertyRange(domain rdfs:Literal) ) Monday, December 21, 2009
- 14. 2.Formal description Monday, December 21, 2009
- 15. • Formal description of the whole distributed system • Concerned with ‘dynamic’ aspects of the system • Use of an extended version of the Pi- Calculus Monday, December 21, 2009
- 16. Formal description of the sample application S(r) GET subscribe n POST n W E A TE S(j) Monday, December 21, 2009
- 17. Formal description of the sample application Processes equations: Monday, December 21, 2009
- 18. 3.Implementation of RESTful semantic services Monday, December 21, 2009
- 19. • 1 RESTful semantic service per OWL/RDFS class in the ontology • Use of the Plaza Framework developed for building RESTful semantic web services Monday, December 21, 2009
- 20. RESTful Semantic Web Service • OWL/RDFS class triples • Exposed as a RESTful resource • Conceptually equivalent to a Linda triple space Monday, December 21, 2009
- 21. Service’s Interface Create POST Read GET Blocking read GET + xblocking header Subscribe • GET + xsubscribe header • Websockets Update PUT Destroy DELETE Monday, December 21, 2009
- 22. RDF Lifting Graph SPARQL query REST Resource triple resource space triple space op. HTTP request Lowering Monday, December 21, 2009
- 23. Plaza Framework Monday, December 21, 2009
- 24. Plaza Framework • Manages ‘Plaza Applications’: OWL ontolgy + configuration module + resources modules • Declarative: almost no coding required • Support for different Java RDF repositories • Automatic managing of triples through the concepts of write-tree and read-tree for the resources • Support for the subscribe operation through chunked HTTP responses and websockets Monday, December 21, 2009
- 25. Sample application configuration module Monday, December 21, 2009
- 26. Sample application exceptions resource module Monday, December 21, 2009
- 27. 4.Implementation of client processes Monday, December 21, 2009
- 28. • Client processes are just REST clients • Required libraries: HTTP and triples format parser (RDF/XML, Turtle, JSON) • Optional support for Websockets • Clojure library included as part of the Plaza Framework Monday, December 21, 2009
- 29. Clojure implementation of the sensor and aggregator processes Monday, December 21, 2009
- 30. Javascript web client using websockets Monday, December 21, 2009
- 31. Web client execution Monday, December 21, 2009
- 32. Conclusions • Semantic technologies enable rich description of problem domains vs. relational modeling • Formal description of distributed systems enables reasoning about its validity and correctness • RESTful semantic web services enable easy access to semantic data • Building RESTful semantic web services clients is trivial due to the use of well known HTTP standard • Triple Space operations are powerful coordination mechanisms for distributed processes Monday, December 21, 2009