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1CONFIDENTIAL
Ajay Bansal, Srividya Kona, Luke Simon, Ajay Mallya, and Gopal Gupta Department of Computer Science University of Texas at Dallas
Thomas D. Hite Metallect Corp.
Dallas, Texas
A Universal Service-Semantics Description Language
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Context and Agenda
• What Web Services *really* are• The next milestone for some ‘better times’• Need for Semantic Services Description• Overview of USDL and an Universal Ontology• Design of USDL• Example USDL annotation of a service• Applications of USDL• Conclusions
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Web Services
Source: W3C Web Services Architecture, W3C Working Draft 14 November 2002
As if this is new info…
Definition:
A Web service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.
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Engaging a Web Service
Source: W3C Web Services Architecture, W3C Working Draft 14 November 2002
Step 2: HUH?
Agree onSemantics???
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Web Services Landscape
• Description– WSDL, SAP (IFR), .NET and Java (Introspection), …– Players: Microsoft, IBM, SAP, Oracle …
• Policy and Security– WS-Policy– Players: IBM, BEA, Microsoft, SAP, Sonic Software, VeriSign
• Composition– BPEL, WSFL and WSCI (older), OWL-S, SWSL, WSML …– Players: Startups, Researchers, Consultants
• Execution– Mostly Proprietary– Players: Oracle, Sun, Microsoft, Tibco, Blue Titan, Actional,
WebMethods…
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Semantics and the average $3B Fortune 1000…• Has hundreds of software applications
– Most of which use different business dictionaries (loosely – taxonomies)– Multiple technologies (programming languages, packaged applications,
databases, middleware)– Millions of lines of source code, database tables/columns, etc.– Multiple metadata repositories– Tens of millions of individual components (functions, variables, DB columns, etc.)
• Spends $105 (70% of total budget) million maintaining those apps
• Has very little visibility into the apps on which they spend:– What they comprise and how they’re interconnected– What software artifacts relate to business drivers and terms– How the ‘guts’ are, or can be, leveraged to meet business needs
• Lack of this kind of visibility is:– A major barrier to IT agility, a driver of cost and a contributor to risk
Solved through Web Services with Automated Semantics
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“Typical” enterprise application infrastructure
Today’s applications are complex, started with different semantic domains, yet are highly interdependent
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Real-life Case Study:A Seemingly Simple Composite Service
Internet Order Application
JavaJ2EE
Web PagesJSP
“Legacy” Order Application
AS/400RPG
MiddlewareOracle
Procedures
AS/400DB2
1. Order placed via web app –invokes Java method(s)
2. Java method interacts with database
3. Oracle DB stores order. A trigger initiates synchronization
4. Middleware transforms and routes order data
5. Middleware transforms and routes order data
6. RPG app processes order and returns status
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Ends up in Complex Human Integration
JSPfor web pages
Javafor order
processing
Oracle for storage and triggers
Middlewarefor trans. and messaging
AS/400 DB2
for storage
AS/400 RPGfor order
processing
Web
Developers
Java
Developers
Oracle
DBA’sMiddleware Engineers
DB2 DBA’sRPG
developers
Distributed Systems Architect
Development Manager
Quality Assurance
Middleware
Architect
AS/400 Architect
Development Manager
Quality Assurance
Enterprise Architect
Quality Assurance
Business Analyst
IT Executive
1 Simple Composite Application1 Simple Composite Application6 Technology Layers, supported by multiple roles & groups6 Technology Layers, supported by multiple roles & groups
Repeat:Repeat: All using All using different terminologies different terminologies for business concepts.for business concepts.
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WSDL
UDDIRegistry
Web Service Provider
Web Service Requester
Describes Service
Points to Description
Points to Service
Finds a Service
Interact via SOAP Messages
Existing Web Service Technologies
• WSDL (Web Services Description Language) • UDDI (Universal Description, Discovery & Integration)• SOAP (Simple Object Access Protocol)
Do not solve the problems for real-
world F1000 companies.
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Automated Semantics, order and RR
Discovery
SolveSolve VerificationVerification
DeclarativeBehaviors
DeclarativeBehaviors
MetadataGenerationMetadata
Generation
WSDLWSDL
OWL-SOWL-S
USSDLUSSDL
OWL-SOWL-S
Java,C/C++,
Etc.
Java,C/C++,
Etc.
Selection
DeployDeploy
Composition
OptimalDesign Rank
OptimalDesign Rank
SemanticServiceDesc
OWL-S…
SWSL
USDL
1 2
30
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Automating Web Services
• Service Discovery– involves automatically locating a service adhering to all the
requested properties.
• Service Execution– involves automatically executing a discovered service that is
appropriate.
• Service Composition– involves automatically selecting, composing & executing
appropriate services for a particular task.
An infrastructure for automation of these tasks was missing!An infrastructure for automation of these tasks was missing!
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Need for Semantic Description of Services
• Infrastructure capable of automation of services must be semantics based.
• Applications should be able to automatically reason about a service's capabilities.
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WSDL Review from the working class
• Purely syntactic in nature.
• Only specifies the format of a service’s program interface (i.e. Call Semantics).
• Does not specify what a service does at a conceptual level.
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Semantic Description Languages
• A couple of good examples:– OWL-S– WSML
• Some limitations:– Use Domain-specific ontology– Semantic aliasing problem
• distinct syntactic representations with distinct formal semantics yet equal conceptual semantics.
– Domain specific ontologies require a formal standardization process (slow) and is not always possible.
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Overcoming the Limitations
• USDL does not preclude or replace OWL-S, WSML or the others.• USDL does address their limitations in atomic service description
• Comprises just a few, easy to grasp components:– A universal ontology: OWL WordNet Ontology– Restricted connectives, such that the semantics always equates things
that are conceptually equal.• Concepts• Affects• Conditions
• In short: a language that service providers and consumers alike can use to easily specify precise, formal and decidable semantics of the services themselves.
Universal Service-Semantics Description LanguageUniversal Service-Semantics Description Language
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Overview of USDL
• Starts with OWL WordNet ontology to provide the missing Semantic semantics of atomic services
• Consists of OWL surrogates for service constructs– PortType and Message are defined in the form of classes and
properties– Formal Language for Service Documentation
• There are only a few things to USDL– Concepts– Affects– Conditions
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OWL WordNet ontology
• A coarse-grained ontology.
• At a conceptual level, it is similar to common real world concepts.
• USDL maps instances of service constructs into OWL WordNet concepts.
• WordNet lexical concepts are used, as opposed to syntactic words, in order to avoid ambiguity of definitions.
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Concept
Atomic Concept
Inverted Concept
Conjunctive Concept
Disjunctive Concept
Subclasses of Concept Class
USDL Concepts
• Generic class Concept is defined in USDL.• Concept class defines the semantics of parts of
messages.
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Atomic Concept
WordNet Lexeme
WordNet Lexeme
isA property
ofKind property
Atomic Concept
• Actual contact point between USDL and WordNet.
• Acts as a proxy for WordNet lexical entities.• Has exactly one defining value for isA property• Has at most one defining value for ofKind property• Example: Atomic Concept OrderNumber isA number
ofKind order.
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USDL Affects
• Semantics of how a service affects the external world is given by the affects property.
• Current design of USDL assumes that each side-effect is one of the following:– creates– updates– deletes– finds
• Generic affects can be used wherein the affects property has USDL Concept as its value.
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USDL Conditions
• Generic class Condition is defined to describe constraints.
• Conditions are represented as conjunction or disjunction of binary predicates.
Condition
Atomic Condition Conjunctive
Condition
Disjunctive Condition
Subclasses of Condition Class
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Atomic Condition
• Condition/Predicate is a trait or aspect of the resource being described.
• An Atomic Condition represents a Predicate which is of type USDL Concept.
• Has exactly one value for onPart property and at most one value for hasValue property.
• Example constraint C1: OrderNumber greater than 1000
Atomic ConditionC1
ConceptgreaterThan
ConceptOrderNumber
Concept1000
hasConcept property
onPart property
hasValue property
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Conjunctive and Disjunctive Conditions:
• Conjunctive condition denotes the conjunction of USDL conditions.
• Disjunctive condition denotes the disjunction of USDL conditions.
• Any n-ary condition can be written as a combination of conjunctions and disjunctions of binary conditions.
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<Message rdf:about="#ReserveFlight_Request"> <hasPart rdf:resource="#CustomerName" /> <hasPart rdf:resource="#FlightNumber" /></Message>
<Message rdf:about="#ReserveFlight_Response"> <hasPart rdf:resource="#ReservationCode"/></Message>
Class Message
• Message class is surrogate for WSDL message.– Message is a composite entity with zero or more
parts.
• For example: FlightReservationService
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Class PortType
• USDL surrogate for WSDL portType.• A collection of procedures or operations that are
parametric on messages.• Has zero or more Operations as values of hasOperation property.
• For example: FlightReservationService.
<PortType rdf:about="#FlightReservation_Service"> <hasOperation rdf:resource="#ReserveFlight" /></PortType>
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Class Operation
• Operation class defines the side-effect of the service via affects property.
• Also defines the input and output messages via hasInput and hasOutput properties.
• For Example: FlightReservationService.<Operation rdf:about="#ReserveFlight"> <hasInput rdf:resource="#ReserveFlight_Request"/> <hasOutput rdf:resource="#ReserveFlight_Response"/> <creates rdf:resource="#ReservationReceipt" /></Operation>
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<definitions> ... <PortType name="BookBuying_Service"> <operation name="BookBuying"> <input message="BuyBook_Request"/> <output message="BuyBook_Response"/> </operation> </PortType>
<message name="BuyBook_Request"> <part name="BookISBN" type="xsd:string"/> <part name="UserIdentifier" type="xsd:string"/> <part name="Password" type="xsd:string"/> </message> <message name="BuyBook_Response"> <part name="OrderNumber/Availability" type="xsd:string"/> </message> ... </definitions>
Example WSDL Description
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<definitions>
<PortType rdf:about="#BookBuying_Service"> <hasOperation rdf:resource="#BuyBook" /> </PortType>
<Operation rdf:about="#BuyBook"> <hasInput rdf:resource="#BuyBook_Request"/> <hasOutput rdf:resource="#BuyBook_Response"/> <creates rdf:resource="#BookOrder" /> </Operation>
<Message rdf:about="#BuyBook_Request"> <hasPart rdf:resource="#BookISBN" /> <hasPart rdf:resource="#UserIdentifier" /> <hasPart rdf:resource="#Password" /> </Message>
<Message rdf:about="#BuyBook_Response"> <hasPart rdf:resource="#OrderNumber/Availabilty"/> </Message>
<AtomicConcept rdf:about="#BookISBN"> <isA rdf:resource="&wn;identifier"/> <ofKind rdf:resource="#Book" /> </AtomicConcept>
<AtomicConcept rdf:about="#BookISBN"> <isA rdf:resource="&wn;identifier"/> <ofKind rdf:resource="#Book" /> </AtomicConcept> <AtomicConcept rdf:about="#Book"> <isA rdf:resource="&wn;book"/> </AtomicConcept>
<AtomicConcept> <isA rdf:resource="&wn;Password"/> </AtomicConcept>
<AtomicConcept rdf:about="#UserIdentifier"> <isA rdf:resource="&wn;identifier"/> <ofKind rdf:resource="#User" /> <hasCondition rdf:resource="#UserExists" /> </AtomicConcept> <Condition rdf:about="#UserExists"> <hasConcept rdf:resource="#exists"/> <onPart rdf:resource="#UserIdentifier"/> </Condition>
… continued on next slide
Example USDL Description
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<AtomicConcept rdf:about="#exists"> <isA rdf:resource="&wn;exists"/> </AtomicConcept> <AtomicConcept rdf:about="#OrderNumber"> <isA rdf:resource="&wn;number"/> <ofKind rdf:resource="#Order" /> </AtomicConcept> <AtomicConcept rdf:about="#Order"> <isA rdf:resource="&wn;order"/> </AtomicConcept> <AtomicConcept rdf:about="#Available"> <isA rdf:resource="&wn;available"/> </AtomicConcept> <AtomicConcept rdf:about="#CreditCard"> <isA rdf:resource="&wn;card" /> <ofKind rdf:resource="#Credit" /> </AtomicConcept>
</definitions>
<DisjunctiveConcept rdf:about="#OrderNumber/Availability"> <hasConcept rdf:resource="#OrderNumber" /> <hasConcept rdf:resource="#NotAvailable" /> </DisjunctiveConcept> <InvertedConcept rdf:about="#NotAvailable"> <hasConcept rdf:resource="#Available" /> </InvertedConcept> <AtomicConcept rdf:about="#BookOrder"> <isA rdf:resource="&wn;order"/> <ofKind rdf:resource="#Book" /> <hasCondition rdf:resource="#CreditExists" /> </AtomicConcept>
<Condition rdf:about="#CreditExists"> <hasConcept rdf:resource="#exists" /> <onPart rdf:resource="#CreditCard" /> </Condition> <AtomicConcept rdf:about="#User"> <isA rdf:resource="&wn;user"/> </AtomicConcept>
Example USDL Description cont’d…
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Applications of USDL
• Formal Semantic documentation of web services.
• Intelligent, conceptual-level querying of directories of web-services.
• Automation of service integration.
• Automation of the development of composite web-services, i.e., web-services implemented via composition of pre-existing web-services.
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USDL and OWL-S
• Atomic services in OWL-S are described using domain-specific ontology– Limits the applicability of OWL-S.– Allows arousal of semantic aliasing problem.
• OWL-S provides tags– presents for service profile– describedBy for service model– For incorporating domain specific ontological descriptions.
• USDL and OWL-S are perfect compliments– USDL describes atomic services within OWL-S.– Overcomes limitation of domain specific ontologies.
OWL-S is a language for composing USDL descriptions.OWL-S is a language for composing USDL descriptions.
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Conclusions
• To make web services ubiquitously available we need a standard formal way of specifying semantics of web services.
• USDL can be used to formally and semantically describe web-services.
• USDL uses OWL WordNet ontology and connectives to provide:– universal ontology:– solves semantic aliasing problem.– does not depend on the process of building domain-specific
ontologies which may have been known to be slow, difficult, and often abandoned.
