developing distributed semantic systems

Building Distributed Semantic Systems

Antonio Garrote Hernández

Monday, December 21, 2009

Definition

• Distributed processes

• Semantic meta data exposed as resources

• Triple space operations

• RESTful interface


Different abstraction levels


Sample application


• 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

Exception logging system


Methodology


4 step process

1. Knowledge modeling

2. Formal description

3. Implementation of RESTful semantic services

4. Implementation of client processes


1.Knowledge modeling


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


Exception

generatedplatform

level message createdAt

ipAddress domain dc:title formatPattern

Node Language

Sample application ontology


Developing the sample application ontology with Protégé


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)

Declaration(DataProperty(level))DataPropertyDomain(level Exception)DataPropertyRange(level rdfs:Literal)

Declaration(DataProperty(ipAddress))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))

Resulting ontologyusing OWL

Functional Notation


http://semantic_rest/exceptions.owl

http://semantic_rest/exceptions.owl

2.Formal description


• Formal description of the whole distributed system

• Concerned with ‘dynamic’ aspects of the system

• Use of an extended version of the Pi-Calculus


S(r)

S(j)

TEAEWGET subscribe n POST n

Formal description of the sample application


Formal description of the sample application

Processes equations:


3.Implementation of RESTful semantic

services


• 1 RESTful semantic service per OWL/RDFS class in the ontology

• Use of the Plaza Framework developed for building RESTful semantic web services


• OWL/RDFS class triples

• Exposed as a RESTful resource

• Conceptually equivalent to a Linda triple space

RESTful Semantic Web Service


Service’s InterfaceCreate POST

Read GET

Blocking read GET + xblocking header

Subscribe • GET + xsubscribe header• Websockets

Update PUT

Destroy DELETE


resourcetriplespace

REST Resource

HTTP request

triple space op.

RDF Graph

SPARQL query

Lifting

Lowering


Plaza Framework


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


Sample application configuration module


Sample application exceptions resource module


4.Implementation of client processes


• 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


Clojure implementation of the sensor and aggregator processes


Javascript web client using websockets


Web client execution


• 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

Conclusions


developing distributed semantic systems

Education

restful resource

javascript web client

web client execution

ontology use

sample application srget

sample applicationmonday

owl ontolgy

description logics