Presented By Venkatavasishta Chemudupati

Outline

IntroductionWeb Services and StandardsModels of Web Services and CompositionAnalysis of Composite ServicesConclusion

IntroductionWhat is Web Services ?

It is defined by the W3C as "a software system designed to support interoperable machine-to-machine interaction over a network". Web services are frequently just Web APIs that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services.

Challenge is to develop modeling techniques and tools to enable their composition and analysis.

In this paper, an overview of assumptions and underlying concepts as well as composition models such are explained.

Anatomy of Web Service Composition

No unified model, e.g., BPEL: Strong on orchestration, info sharingOWL-S: Strong on goals, activities, discovery“Roman” model: Strong on activities,

orchestration

Goal(s)

Activities

Infosharing(Messaging)

Orchestration,Monitoring

Discovery/Self-description

Key dimensions in web service composition

OWL-S

“sem

anti

cs”

Roman

Complexity of component services

Complexity of glue languageMealy

-CalcWSCL

CTR-S

BPMLBPEL

CSP

WSDL

Commitment Protocols

Outline

IntroductionWeb Services and StandardsModels of Web Services and CompositionAnalysis of Composite ServicesConclusion

Web Services Standards Stack: Key Elements

HTTP, SMTP, FTP, etc.

SOAP

OWL-S ServiceProfice

Network

XMLMessaging

(Individual)ServiceDescription

WSCL

WSDL

Composition BPEL4WS

Choreography WS-Choreorgaphy

Discovery UDDI

OWL-S ServiceModel

Simple Object Access ProtocolA W3C standardOriginally developed for BizTalkA light weight replacement for complicated

distributed object technology

“XML-RPC”, typically through HTTP, also JMS …Lowest level of service interaction

ExternalService

WebService

WebServer

SOAP Envelope

Web Service Definition Language (WSDL) WSDL provides a framework for defining

Interface: operations and input/output

Access specification: SOAP bindings (e.g., RPC)

Endpoint: the location of service

OperationPort Type

MessageBinding

Port Service

Supports

Input & Output

Provides

How to encode

Formats & Protocols

How to invoke

Implements

Web Service Conversation Language (WSCL)

A key to web service composition:Interactions between services

WSCL specifies a conversation (behavior signature) as a labeled graph:Nodes: interactions, individual units of responsesEdges: transitions, sequencing of interactionsEdge labels: conditions on transitions

Business Process Execution Language (BPEL)

Allow specification of compositions of Web servicesbusiness processes as coordinated interactions of

Web servicesAllow abstract and executable processesInfluences from

Traditional flow modelsStructured programmingSuccessor of WSFL and XLANG

Assumes WSDL portsStandardization through OASIS

Outline

IntroductionWeb Services and StandardsModels of Web Services and CompositionAnalysis of Composite ServicesConclusion

OWL-S: Model and Composition

OWL-S is an ontology built on top of Web Ontology Language (OWL) by the DARPA DAML program. It replaces the former DAML-S ontology. "OWL-S is an ontology, within the OWL-based framework of the Semantic Web, for describing Semantic Web Services.

It will enable users and software agents to automatically discover, invoke, compose, and monitor Web resources offering services, under specified constraints.

Here we adopt the approach recently introduced by work by work on First-order Logic Ontology for Web Services (FLOWS) as it is somewhat closer to relational database formulation than originally used by OWL-S.

Functionality Description Preconditions

Set of conditions that should hold prior to service invocation Inputs

Set of necessary inputs that the requester should provide to invoke the service

Outputs Results that the requester should expect after interaction with

the service provider is completed Effects

Set of statements that should hold true if the service is invoked successfully

Often refer to real-world effects, e.g., Package being delivered, or Credit card being debited

OWL-S Example

Process Specification LanguageA recent ISO standard which is first order logic ontology

for describing the core elements of processes.PSL is layered with PSL-Core at base and many

extensions viz. PSL-OuterCore.PSL-OuterCore provides first-order predicates that can be

used as basic building blocks of processes and execution.

In a typical usage, application domain is created by combining PSL-OuterCore with domain specific predicates and sentences to form theory.

The models of theory can be thought of as a tree, whose nodes are activities with edges from one occurrence to another.

A path can be viewed as one possible execution of steps.

OWL-S and PSL CombinedNow, to provide a database-oriented cast on

PSL and OWL-SThe PSL and domain-specific predicates

associated with our example can be viewed essentially as relations in a relational database. So, we might have

Results concerning automatic composition of OWL-S

In first one, it is assumed that all relevant aspects of application domain are represented using finite number of propositional fluents and permitted input and output is finite.

The goal is then specified in terms of overall effect to be achieved starting from initial state.

Another approach proposes a two tier framework based on generic programs and customization via constraints.

Roman Model perspectiveThis involves automated composition of multi-step

services.Basically, there is a finite alphabet of activity

names, but no internal structure is modeled.In the most general case, these are potentially

infinite trees, where each branch corresponds to a permitted sequencing of executions of the activities.

For the theoretical results they restrict attention to finitely specifiable transition systems; in particular on systems that can be specified as deterministic finite-state automata, where the activities act as the input alphabet

Example for Roman Model

Example Contd…

Conversations and Mealy Services

The OWL-S and Roman focus on what a service does in terms of input/output and their impact on world or sequencing the activities, neither address how component services should interact with each other.

We assume an infinite set of message classes, where each class mc has service name as source and target.

A compositions schema is a pair (P,M) where P is finite set of service names and M finite set of message classes.

Composition Schema

FLOWS

FLOWS – It includes objects of type service. These can be related to several types of object, including non-functional properties and also its activity.

Flow of information between services can occur in two ways 1. Message Passing2. Shared access to same “real world”

It is a very open-ended concerning process or data flow between atomic processes inside a services.

COLOMBOA formal model it combines

1. A world state, representing the \real world", viewed as a database instance over a relational database schema

2. Atomic processes in the spirit of OWL-S,3. Message passing, including a simple

notion of ports and links, as found in web services standards (e.g., WSDL, BPEL)

4. An automata-based model of the internal behavior of web services, where the individual transitions correspond to atomic processes, message writes, and message reads.

Contd…5. A “local store” for each web service, used

manage the data read/written with messages and input/output by atomic processes

6. a simple form of integrity constraints on the world state

Analysis

Conclusion1. To Find appropriate models and abstractions for

representing Web services and their “behaviors”, which are suitable to the web services paradigm, and can support efficient querying and manipulation as needed by web service composition and analysis algorithms.

2. How to bring data manipulation more clearly into web services paradigm and their associated standards.

3. Are there specialized models of Web service composition that will be more suitable for applications that are targeted primarily at data processing ?

Thank You !!!