Post on 18-Dec-2015
RATS Oct 2002 CS@UGA
PrefaceI 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 CS@UGA
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 CS@UGA
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 CS@UGA
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 CS@UGA
Evolution:
Application Application
Application Application
ApplicationApplication
API
API
SOAP LAYER
User Interaction
User Interaction
RATS Oct 2002 CS@UGA
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 CS@UGA
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 CS@UGA
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 CS@UGA
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 CS@UGA
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
ServiceRequestor
Publish Find
Bind
RATS Oct 2002 CS@UGA
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 CS@UGA
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 CS@UGA
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 CS@UGA
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 CS@UGA
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 registryStep 2: Service requesters (consumer) search registries
for servicesStep 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 CS@UGA
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 CS@UGA
courtesy:http://www.cs.uga.edu/~sent/thesis/Final.ppt
Simple Web Service Invocation
RemoteWeb ServiceRepository(Web Sites)
WriteClient Code
Service Requestor
Invoke Web Service
Manual Web Service
Lookup
SOAP Request
SOAP Response
WSDL File
Remote Web service
Publish Web Service
1
2
3
4
5
HTTP GET
RATS Oct 2002 CS@UGA
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://www.cs.uga.edu/~sent/thesis/Final.ppt
(http transport)Requestor
SOAP Messages
Web Service ProviderEndpoint
SOAP Client
RATS Oct 2002 CS@UGA
WSDL* Structure Service
collection of endpoints endpoints= port + binding
Port typeset of operations supported by endpoints
Operationsabstract description of action supported by service
Bindingmaps abstract specification to specific protocol
Portsnetwork address/URI that implements service
Messagetyped definition of data communicated
* Used in conjunction with UDDI registry and can be compared with IDLcourtesy: http://www.llnl.gov/CASC/workshops/components_2001/viewgraphs/FranciscoCurbera.ppt
Service
Port(e.g. http://host/svc)
Binding(e.g. SOAP)
Abstract interface
portType
operation(s)
inMesage outMessage
Port
Binding
RATS Oct 2002 CS@UGA
WSDL File
ConcreteDescription
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
AbstractDescription
RATS Oct 2002 CS@UGA
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 CS@UGA
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
<?xml version="1.0" encoding="UTF-8" ?> <env:Envelope xmlns:env="http://www.w3.org/2001/09/soap-envelope"> <env:Header>
<n:alertcontrol xmlns:n="http://example.org/alertcontrol"> <n:priority>1</n:priority> <n:expires>2001-06-22T14:00:00-05:00</n:expires> </n:alertcontrol>
</env:Header> <env:Body>
<m:alert xmlns:m="http://example.org/alert"> <m:msg>Pick up Mary at school at 2pm</m:msg>
</m:alert> </env:Body></env:Envelope>
courtesy: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnsoapspec/html/soapspecindex.asp
RATS Oct 2002 CS@UGA
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 CS@UGA
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 CS@UGA
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 CS@UGA
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 CS@UGA
Wrap upHopefully you understood in this session:
1. what a web service is2. advantages of using it3. value addition by composition4. what has been done so far in web services?5. what can be done in future w.r.t. WS?
RATS Oct 2002 CS@UGA
Questionsand hopefully answers mailto:kaart@cs.uga.edu http://www.arches.uga.edu/~kaarthik
RATS Oct 2002 CS@UGA
For more information: http://www.uddi.org http://www.w3.org/2002/ws/ http://java.sun.com/webservices/docs/1.0/tutorial/ http://www.alphaworks.ibm.com/webservices http://edocs.bea.com/wls/docs70/webserv/index.html http://xml.apache.org/ http://www.xml.com/pub/a/2001/04/04/webservices/ http://www-3.ibm.com/software/solutions/webservices/ http://www.w3c.org/TR/wsdl http://www.w3c.org/TR/soap http://chief.cs.uga.edu/~jam/webwork/geneflow/papers/wspapers.html