Silicon Valley Semantic Web Meet Up

www.sti-innsbruck.at © Copyright 2008 STI INNSBRUCK www.sti-innsbruck.at

Semantic Web services in a Nutshell

Federico M. Facca and Reto Krummenacher

www.sti-innsbruck.at 2

Federico M. [email protected]

Reto [email protected]

http://www.sti-innsbruck.at


Semantic Technology Institute Innsbruck

• Institute at the University of Innsbruck (est. 1669) which is currently the largest education facility in Austria.

• Founded as a research group under the guidance of Prof. Dieter Fensel in 2003.

• Status of a research institute at the University of Innsbruck since January of 2006.

• Main research areas: Semantic Web, Semantic Web Services, Service-Oriented Architectures.

www.sti-innsbruck.at

Projects

• Currently involved in a number of FP6 and FP7 EU projects related to the Semantic Web and Semantic Web Services such as

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STI International


Making this real…STI International

• The mission of Semantic Technology Institute International is to establish semantics as a core pillar of modern computer science.

• STI is organized as an association of jointly interested academic, industrial and governmental parties.

• It provides services to facilitate research, education, and commercialization activities around semantic technologies and the service web beyond the boundaries of individual projects or initiatives.


STI International – The Members


The Future Internet


Overview

• Background and Motivation• Service Web• Semantic Web Services• SOA4All: A Global Service Delivery Platform• Highly Flexible Service Offer for the Future Internet• Conclusion


BACKGROUND

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The Rise of the Service Economy

[IBM Survey on national labor data, 2004]

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Background

• Computer science is entering a new generation – The previous generation was based on abstracting from

hardware– The emerging generation comes from abstracting from software

and sees all resources as services in a service-oriented architecture (SOA)

• In a world of services, it is the service that counts for a customer and not the software or hardware components that implement the service

• Service-oriented architectures are rapidly becoming the dominant computing paradigm

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From SaaS to XaaS

• In a service-oriented world everything is a service– Programs are services– Devices are services– Different types of media (audio, video, text) are

integrated– Environments are dynamic and open– Mobility; Ubiquity; RFID

• Service orientation needs to scale up to open and dynamic environments of billions of services

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XaaS: Amazon – S3 & EC2

• “Infrastructure as a service”

• Amazon Simple Storage Service (S3)– Write and read objects up to 5GB– 15 cents GB / month to store– 20 cents GB / month to transfer

• Amazon Elastic Compute Cloud (EC2)– allows customers to rent computers – on which to run their own computer – applications– virtual server technology– 10 cents / hour

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State of affairs

• Current SOA solutions are however still restricted in their application context to companies’ intranets

• A ‘Service Web’ with billions of services depends on resolving fundamental challenges that SOA does not address currently

• Currently there exists only around 30000 Web services on the Web

Number of Web services found during the past 26 months [seekda.com, August 2009]

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SERVICE WEB

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Requirements for Service Web

A Service Web with billions of services can be realized only if SOA can deal with

– Openness – everybody can act as a provider or consumer of services

– Heterogeneity – services are created in isolation from one another thus interoperability is an issue

– Distributedness – there is no central control of services. Services can appear, change or disappear at any time in an uncontrolled fashion

– Scalability – with so many services available on the Service Web the Human may become the bottleneck

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How to enable Service Web?

• A Web-scale service delivery platform– Any time and anywhere

service consumption– Heterogonous execution

platforms

• New paradigms to engineer, integrate, deploy services– Flexibility– Customization

• Semantics as scalability enabler– Service customization– Service federations

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[Prof. dr. Lutz Heuser, SAP: “Towards afuture Internet of Services”]


Semantics and Service Web

• Semantics is a required key enabler for automation of the service life-cycle at Web-scale, but if misused it may become a bottle-neck

• It does not make sense to describe (or assume that) Amazon services in a complete way (i.e. using ~30 billions RDF triples!)

– In a world of billions of services it may cost too much to find the “optimal” service in relation to the reward of having actually found the optimal solution

– Pragmatic approaches in service discovery will focus on utility, i.e., stop the search process when a service is found that is “good” enough to fulfill a request

– Also, it is unrealistic to assume that semantic descriptions of services are correct and complete, i.e., duplicate the functionality of a service at the description level

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SEMANTIC WEB SERVICES

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Semantic Web and Web Services

Static WWWURI, HTML, HTTP

Semantic WebRDF, RDF(S), OWL, etc.

Dynamic Web ServicesUDDI, WSDL, SOAP

Semantic WebServices

It’s all about automation!


Top-level elements defined by WSMO

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Objectives that a client may have when consulting a Web Service

Semantic description of WebServices: • Capability (functional)• Non-functional properties• Interfaces (usage)

Connectors between components withmediation facilities for handling

heterogeneities

Provide the formallyspecified terminology

of the information usedby all other components


Ontologies

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Ontologies

• In WSMO, Ontologies are the key to linking conceptual real-world semantics defined and agreed upon by communities of users

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Examples:• The Location Ontology

(http://www.wsmo.org/ontologies/location) contains the concepts “Country” and “Address”

• The Location Ontology (http://www.wsmo.org/ontologies/location) contains the “Austria” and “Germany” instances

Class ontology sub-Class wsmoElement importsOntology type ontology

usesMediator type ooMediator hasConcept type concept hasRelation type relation hasFunction type function hasInstance type instance hasRelationInstance type relationInstance hasAxiom type axiom


Ontology Specification

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• Non functional properties author, date, ID, etc. • Imported Ontologies importing existing ontologies

where no heterogeneities arise • Used mediators OO Mediators (ontology import with

terminology mismatch handling)

Ontology Elements:Concepts set of entities that exists in the world / domain

Attributes set of attributes that belong to a concept

Relations define interrelations between several concepts

Functions special type of relation (unary range = return value)

Instances set of instances that belong to the represented ontology

Axioms axiomatic expressions in ontology (logical statement)


The Web Service Element

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The Web Service Element

• WSMO Web service descriptions consist of non-functional, functional, and the behavioral aspects of a Web service

– A Web service is a computational entity which is able (by invocation) to achieve a users goal. A service in contrast is the actual value provided by this invocation

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Web Service Non-Functional Properties

• Non-functional properties:– Accuracy - the error rate generated by the service– Financial - the cost-related and charging-related properties of a service – Network-related QoS - QoS mechanisms operating in the transport network

which are independent of the service– Performance - how fast a service request can be completed– Reliability - the ability of a service to perform its functions (to maintain its service

quality)– Robustness - the ability of the service to function correctly in the presence of

incomplete or invalid inputs. – Scalability - the ability of the service to process more requests in a certain time

interval– Security - the ability of a service to provide authentication, authorization,

confidentiality, traceability/auditability, data encryption, and non-repudiation – Transactional - transactional properties of the service– Trust - the trust worthiness of the service

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Example:• If the client is older than 60 or younger than 10 years old the invocation price is lower than 10 euro


Web Service Capability

• A capability defines the Web service by means of its functionality

• Precondition - the information space of the Web service before its execution• Assumption - the state of the world before the execution of the Web service• Postcondition - the information space of the Web service after the execution of the

Web service• Effect - the state of the world after the execution of the Web service• Shared Variables - variables that are shared between preconditions, postconditons,

assumptions and effects

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Example:• The input for a birth registration service

in Germany has to be boy or a girl with birthdate in the past and be born in Germany. The effect of the execution of the service is that after the registration the child is a German citizen.

Class capability sub-Class wsmoElement importsOntology type ontology usesMediator type {ooMediator, wgMediator} hasNonFunctionalProperties type nonFunctionalProperty hasSharedVariables type sharedVariables hasPrecondition type axiom hasAssumption type axiom hasPostcondition type axiom hasEffect type axiom


Web Service Interface

• An interface describes how the functionality of the Web service can be achieved (i.e. how the capability of a Web service can be fulfilled) by providing a twofold view on the operational competence of the Web service:

– Choreography decomposes a capability in terms of interaction with the Web service

– Orchestration decomposes a capability in terms of functionality required from other Web services

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Class interface sub-Class wsmoElement importsOntology type ontology usesMediator type ooMediator hasNonFunctionalProperties type nonFunctionalProperty hasChoreography type choreography hasOrchestration type orchestration


Goals

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Goals

• Goals are representations of an objective for which fulfillment is sought through the execution of a Web service. Goals can be descriptions of Web services that would potentially satisfy the user desires

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Example:• A person named Paul has to goal to register his son with the German birth registration board

Class goal sub-Class wsmoElement importsOntology type ontology usesMediator type {ooMediator, ggMediator} hasNonFunctionalProperties type nonFunctionalProperty requestsCapability type capability multiplicity = single-valued requestsInterface type interface


Example: Web Service Discovery

• Distinguish between abstract service and a specific one– Abstract service: a computational entity able to provide many

services– Service: a concrete invocation of a Web service

• The task– Client is interested in getting a specific service– Identify possible service providers, which may be able to provide

the requested service S for its clients

• Discovery– Given a goal and some Service repository determine the set of

relevant service providers

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Example: Web Service Discovery

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Goal: buy a travel ticket from

Vienna to Berlin

Web service: sells train tickets

for trips within Europe

Reasoning

Match!

Europe

Vienna&

Berlin

Travel Ticket

TrainTicket


Mediators

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Mediators

• Mediation– Data Level - mediate heterogeneous Data Sources – Protocol Level - mediate heterogeneous Communication

Patterns – Process Level - mediate heterogeneous Business Processes


Mediators

• Four different types of mediators in WSMO– ggMediators: mediators that link two goals. This link represents

the refinement of the source goal into the target goal or state equivalence if both goals are substitutable

– ooMediators: mediators that import ontologies and resolve possible representation mismatches between ontologies

– wgMediators: mediators that link Web services to goals, meaning that the Web service (totally or partially) fulfills the goal to which it is linked. wgMediators may explicitly state the difference between the two entities and map different vocabularies (through the use of ooMediators)

– wwMediators: mediators linking two Web services


The WSMO Framework

Execution Environment for SWS

Conceptual Model for SWS

Formal Language for WSMO

Ontology & Rule Language for the Semantic Web


SOA4All: A GLOBAL SERVICE DELIVERY PLATFORM

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Motivation

• The Web currently contains 30 billion Web pages• Children can create Web pages

• BUT the Web contains only ~28,000 ‘true’ Web services (seekda.com)

• Only technologically experienced people can create and work with Web services


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Two Core Objectives

• “Billion of Services”: SOA4All will transform the Web into a domain where billions of parties are exposing and consuming services in a seamless and transparent fashion.

• “4 All”: SOA4All will integrate the service world of large enterprises, SMEs, and end-users enabling them to engage as peers within a network of equals.

http://www. .eu


Approach

Web: openness, decentralization, n:m relations, statelessness

Web2.0: content prosumers, service prosumers, communities

Context: user profiles, execution monitoring, service data, social context

Semantics: formal models, service and goal descriptions, processes


SOA4All Architecture

‘semantic service descriptions’ ‘semantic process descriptions’‘semantic goal descriptions’


Semantic Spaces

• Use of semantics in SOA4All requires a scalable and distributed data management infrastructure for:– Repository for service annotations in RDF– Infrastructure for sharing monitoring and execution data– Process repository of composition information– User profile management infrastructure

• Semantic Spaces provide:– Web-style publish and read operations (persistent storage) – Shared data management– Interaction mechanism for collaborative activities– Event-based notification services


Annotation of Services

Representation LanguagesWSML

Annotation MechanismsWSMO-Lite, MicroWSMO

Reasoners


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?

Annotation of Services

?s=HanivalCreditCheck?s=PayPalCreditService?s=...

ontology FinancialServices concept CreditCheckService subConceptOf FinancialService ...."?s[modelReference hasValue ?cat]

memberOf wsl#Service and?cat subConceptOf FinancialService"

<service name="HanivalCreditCheck" sawsdl:modelReference= "http://ex.com/FinancialServices# CreditCheckService" ...

Reasoner


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Lightweight Service Modelling

A common service model is expressed in RDF Schema, using only the WSMO features motivated by SAWSDL references

WS-* Stack services attached to lightweight semantic descriptions via SAWSDL

RESTful services attached to lightweight semantic

descriptions via microformants


WSDL Simplified

Web service

Operation 1input

output

... Operation 2

input

output

Operation Ninput

output


Semantics in Service Model

Web service

Operation 1input

output

... Operation 2

input

output

Operation Ninput

output

F N B I

Functional, Non-Functional, Behavioural, Information model

SAWSDLmodelReference


MicroWSMO

• The service is described for humans on a Web page

• hRESTS allows aspects of the service description to be annotated• microWSMO uses these annotations to refer to elements of the same lightweight service modelling ontology as WSMO-Lite


WSMO-Lite Annotation Tool

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Goal Formalisation

• Semantic goal descriptions match the WSMO-Lite service annotations.

• SPARQL can be used as simplest discovery algorithm by matching operations, input, and output messages.

• More sophisticated matching (based on conditions, effects or NFPs) requires axiomatic reasoning (e.g. WSML).


Example: Service Discovery

SOA4All Studio: Consumption PlatformSOA4All Studio: Consumption Platform

SOA4All Runtime: DSB & Platform ServicesSOA4All Runtime: DSB & Platform Services

DiscoveryDiscovery

Ranking & SelectionRanking & Selection

ReasonerReasoner

Service RegistryService Registry

Craw

ler

Craw

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Semantic SpaceSemantic Space

Com

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via

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Example: Service Discovery

SOA4All Studio: Consumption PlatformSOA4All Studio: Consumption Platform


DiscoveryDiscovery

Ranking & SelectionRanking & Selection

ReasonerReasoner

Service RegistryService Registry

Craw

ler

Craw

ler


Com

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OO

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Service Composition

SOA4All Studio: Provisioning PlatformSOA4All Studio: Provisioning Platform


„DISCOVERY“„DISCOVERY“


Design-Time ComposerDesign-Time Composer

Execution EngineExecution Engine

Composition OptimizerComposition Optimizer

Template GeneratorTemplate Generator

ReasonerReasoner

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Communication via DSB

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Service Composition

SOA4All Studio: Provisioning PlatformSOA4All Studio: Provisioning Platform


„DISCOVERY“„DISCOVERY“


Design-Time ComposerDesign-Time Composer

Execution EngineExecution Engine

Composition OptimizerComposition Optimizer

Template GeneratorTemplate Generator

ReasonerReasoner

Communication via DSB

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HIGHLY FLEXIBLE SERVICE OFFER FOR THE FUTURE INTERNET

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From one that fits allto personalized software

• Traditional software engineering and provisioning solutions suffer from lack of flexibility– A software to fits all type of customers

• Modern trends in products variability showed how customization increase revenues– Web scale delivery of customized software– How can we achieve mass customized software as with traditional

products?

• Economy showed that the only way to enable small competitors to stay on the market is by federating and providing high-added-value service bundles– Dynamically created federations of services to better match user’s

demand– How can we enable providers to federate together at web-scale with a high

degree of automation?

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Parametric Services and Semantics

• High level service customization can be achieved by making services parametric

• Automatic deploy-time and run-time customization of parametric services requires proper languages and methods

• Semantics enable description of such aspects and automatic reasoning over them through application of problem solving methods and parametric design

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Service Federations and Semantics

• Global scale delivery of services, including services provided by small providers can be achieved by automated federation of services

• Requires tools and languages for enabling negotiation among services and service providers

• Semantics is the means to enable negotiation among providers, supporting heterogeneity resolution and making possible optimization of the federation via reasoning techniques and problem solving methods

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CONCLUSIONS

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Conclusion

Future Internet requires:

• Platforms and languages for Service Web• Methods and languages for mass customization of

services• Semantic Web techniques can be used to provide

approximate descriptions of services …• … however not as a replacement of service technology.

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Summary

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Web services stagnate Global service delivery

Semantic Web services SOA4All