Web Services Kaarthik Sivashanmugam Department of Computer Science The University of Georgia

RATS Oct 2002 Preface I assume you all know that this is just an introductory session to web services you all know XML you will ask questions we all will enjoy this session

RATS Oct 2002 Purpose of this session Introduction to web services enabling technologies: SOAP, WSDL, UDDI etc Understanding need for web services web services jargons Foresee challenges Discuss my work

RATS Oct 2002 What are Web Services ? Web services are modular web applications that provide data and services to other applications over the web Web services apply web technologies such as HTTP and XML to the concepts of distributed computing technologies such as CORBA and DCOM

RATS Oct 2002 Present Web: Common man’s comment: It is awesome. information sharing B2C, B2B search, mail, chat, RPC and what not? What is missing? automated interactions commonness between different distributed application technologies

RATS Oct 2002 Evolution: Application API SOAP LAYER User Interaction

RATS Oct 2002 Evolution (contd) Need for betterment Tomorrow’s Web: automated interactions application level interactions distributed computing platform Answer: web services Goals: enable internet scale dynamic binding efficiently support both open web and more constrained environments universal availability and interoperability

RATS Oct 2002 Vision: Unified view of applications in heterogeneous systems on web Seamlessly integrate with existing platforms and programming models Distributed computing platform for the web Interface to access functionalities offered by information systems, application programs and business processes

RATS Oct 2002 Web Service: Definition A Web service is a software application identified by a URI, whose interfaces and binding** are capable of being defined, described and discovered by XML artifacts and supports direct interactions with other software applications using XML based messages via Internet-based protocols. (W3C definition) **- An association between an Interface, a concrete protocol and a data format

RATS Oct 2002 Web Service: Definition (contd) Web services are self contained, self- describing, modular applications that can be published, located, and invoked across the Web. (Tidwell, IBM, 2001) Web service applications are encapsulated, loosely coupled Web “components” that can bind dynamically to each other. (Curbera, IBM, 2001)

RATS Oct 2002 Web Services: Features Service Oriented Architecture (SOA) as opposed to application based (client-server, monolithic) architectures Web is a collection of services Service Registry Service Provider Service Requestor PublishFind Bind

RATS Oct 2002 Features(contd) Create loosely coupled applications changing implementation of a function does not require change in invoking function Create encapsulated applications implementation is hidden from outside Allows integration of applications with deep interaction applications are unaware of APIs

RATS Oct 2002 Features(contd) Allow reuse of Software Components reusable code that need not be written saving time, money and reducing risk Address Middleware issues over web without much complexity FYI: Middleware is a high level software layer that provides a standardized interface to collection of distributed objects FYI: What’s wrong with CORBA/RMI/COM ? don’t talk to each other (some implementations do) tightly coupled with application different data representation, vendors and dialects RMI: Java-to-Java only technology CORBA: uses proprietary IIOP (typically blocked by Firewall) and interoperability of ORB implementations is not guaranteed COM/DCOM: Microsoft only solution

RATS Oct 2002 Features(contd) Based on messages, documents and not APIs shift in focus from ‘how to invocate’ to ‘what to invocate’ Can be complementary to CORBA, RMI, COM components are treated as services using WSDL *1 as extended IDL *2 Common registry cross vendor, platform, industry widely accepted *1 Web Services Description Language *2 Interface Description Language

RATS Oct 2002 Features(contd) Operating system agnostic because it is XML (simple structured text) based technology Consistent architecture both inside and outside an enterprise application producer/consumer in different hardware regardless of development environment Allows composition combining and linking existing web services to create new web processes to perform a complex task

RATS Oct 2002 How Web Services work? Web services are standards-based software components that can be accessed over the Internet. Step 1: Service providers (producer) maintain/publish information about their services in a registry Step 2: Service requesters (consumer) search registries for services Step 3: Once found, a service can be invoked based on open Internet standards irrespective of differences in platforms, programming model, programming languages between consumer and producer

RATS Oct 2002 Web Services Standards With the following technologies, it is possible to build standards-based systems that are truly interoperable. UDDI: Universal Description, Discovery and Integration. UDDI registry stores descriptions about companies and the services they offer in a common XML format. (for web services publishing and discovery) WSDL: Web Services Description Language (new: DAML-S) WSDL is an XML-based format for specifying the interface to a web service. (for web services description) SOAP: Simple Object Access Protocol SOAP is the XML-based protocol for sending requests and responses to and from web services. (for web services invocation) WSFL: Web Services Flow Language (new: BPEL4WS) for web services composition

RATS Oct 2002 courtesy: Simple Web Service Invocation Remote Web Service Repository (Web Sites) Write Client Code Service Requestor Invoke Web Service Manual Web Service Lookup SOAP Request SOAP Response WSDL File Remote Web service Publish Web Service HTTP GET

RATS Oct 2002 Behind the scene Components required software which needs to be exposed as a web service SOAP Server (Apache Axis, SOAP::Lite, etc.) HTTP Server (if HTTP is used as the transport level protocol) SOAP Client (Apache Axis, SOAP::Lite etc.) Deployment: registering with SOAP server with details about the code to execute when requested Invocation: requesting for some service. Could be done with any SOAP client. courtesy: (http transport) Requestor SOAP Messages Web Service Provider Endpoint SOAP Client

RATS Oct 2002 WSDL * Structure Service collection of endpoints endpoints= port + binding Port type set of operations supported by endpoints Operations abstract description of action supported by service Binding maps abstract specification to specific protocol Ports network address/URI that implements service Message typed definition of data communicated * Used in conjunction with UDDI registry and can be compared with IDL courtesy: Service Port (e.g. Binding (e.g. SOAP) Abstract interface portType operation(s) inMesageoutMessage Port Binding

RATS Oct 2002 WSDL File Concrete Description Provides explicit representation of available protocols while in OMG model, protocol is fixed at the time ORB infrastructure is deployed. Protocol specification is not visible to application or developer Abstract Description

RATS Oct 2002 SOAP: Simple Object Access Protocol XML based lightweight protocol for the exchange of information in a decentralized, distributed environment What's so special about SOAP ? platform independent gets over firewall issues Why do we need it ? today's applications communicate using RPC using HTTP. But HTTP is not designed for this.  introduces security and compatibility issues  firewalls typically block How ? XML based messages (simple text and nothing else)

RATS Oct 2002 SOAP: SOAP defines a framework for message structure and a message-processing model Does not define application semantics Enables trans-operating system RPCs Used over HTTP, SMTP, FTP, MQSeries, Jabber, JMS etc T14:00:00-05:00 Pick up Mary at school at 2pm courtesy:

RATS Oct 2002 UDDI A shared public registry implementation based on a set of public specifications Specification for registry also defines a SOAP-based web service for locating WSDL-formatted protocol descriptions of web services Two types of information are registered within UDDI. The first is the set of abstract service protocols, called tModels (technical models), which are used to describe the behavior of a web service. The second type of information in UDDI is the service implementation, currently referred to as a businessEntity. These entries refer to multiple tModels and provide descriptions about their behavior and specifications.

RATS Oct 2002 Web Services Composition Task of combining and linking existing web services to create new web processes. WHY ? (e.g.. Conference booking scenario) Adds value to the collection of services, by orchestrating them according to the requirement of the problem Types of Composition Static Composition - services to be composed are decided at design time Dynamic Composition - services to be composed are decided at run-time WSFL, XLANG, BPEL4WS, DAML-S are some of the XML languages that have been proposed for specifying a web service composition

RATS Oct 2002 Challenges and my ongoing work in Web Services Semantics based discovery of web services WSDL, UDDI do not support description and publishing services based on capabilities present discovery is based on key word search (e.g.. “Ticket Service”). Not efficient. solution: Ontology based description and discovery of web services achieves semantic mark up to web services and provides semantic interoperability Dynamic composition QoS, service agreements, security Harmonizing transactional behavior, reliably executing and monitoring messages

RATS Oct 2002 Summary Web Services framework is being defined, standardized standards are still in flux received wide acceptance in industry as an e-business (r)evolution provides increased flexibility in software deployment offers a cost effective way to maintain and integrate legacy IT systems at a lower cost than typical enterprise application integration efforts could be next-generation EDI could be used as middleware for internet level applications

RATS Oct 2002 Wrap up Hopefully you understood in this session: 1. what a web service is 2. advantages of using it 3. value addition by composition 4. what has been done so far in web services? 5. what can be done in future w.r.t. WS?

RATS Oct 2002 Questions and hopefully answers

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