1. Sabri Kızanlık Ural Emekçi
WEB SERVICES
Sabri Kızanlık
Ural Emekçi

2. Agenda
Web Service definition
Extensible Markup Language
Simple Object Access Protocol
WSDL
UDDI
Service Oriented Architecture

3. Web Service definition
An open standard for accessing component-based applications
Core Web services standards include XML, WSDL, SOAP and UDDI
Advanced Web services provide support for security, transactions, reliability, business processes, and management
Web services evolved from previous technologies that served the same purpose such as RPC, ORPC (DCOM, CORBA and JAVA RMI).
Web Services were intended to solve three main problems:
Interoperability
Firewall traversal
Complexity

4. Service Standards
XML – eXtensible Markup Language – A uniform data representation and exchange mechanism.
SOAP – Simple Object Access Protocol – A standard way for communication.
UDDI – Universal Description, Discovery and Integration specification – A mechanism to register and locate WS based application.
WSDL – Web Services Description Language – A standard meta language to described the services offered.
XML – eXtensible Markup Language – A uniform data representation and exchange mechanism.
SOAP – Simple Object Access Protocol – A standard way for communication.
UDDI – Universal Description, Discovery and Integration specification – A mechanism to register and locate WS based application.
WSDL – Web Services Description Language – A standard meta language to described the services offered.

5. Web Services Specifications
Communicates via open protocols (HTTP, SMTP, etc.)
Processes XML messages framed using SOAP
Describes its messages using XML Schema
Provides an endpoint description using WSDL
Can be discovered using UDDI

6. An Example Two endpoints: Client & Seller
The Client finds the Seller by searching UDDI directory.
The Service of Seller is designed using WSDL.
The Client gets the service by using SOAP.
The Client takes a SOAP reply defined in WSDL.
A buyer (which might be a simple client) is ordering goods from a seller service.
The buyer finds the seller service by searching the UDDI directory.
The seller service is a Web Service whose interface is defined using Web Services Description Language (WSDL).
The buyer is invoking the order method on the seller service using Simple Object Access Protocol (SOAP) and the WSDL definition for the seller service.
The buyer knows what to expect in the SOAP reply message because this is defined in the WSDL definition for the seller service.

7. Model
The service registry role owns a directory of all of the services available. The service
registry represents a new, potentially very lucrative business model. The Registry
owner could charge a fee for the use of their directory. Service Providers lists (or
advertise) the Service offering in the registry. Service Requesters on the other hand
query the service registry about the services available. Once service registry provides
the binding information to the requester, it is no longer involved in the communications
between the provider and requester. The service registry has been grayed-out as this
presentation will focus on the Service Requester - Service Provider interaction.
--- The Service Provider has developed services that they make available as Web Service.
These services will be hosted on their application server. A service is invoked by a requester through an XML message. These XML messages are generally carried
across the Internet through a network-neutral standard protocol called SOAP. The
Service Provider describes the service they are making available with a standard
encoding called Web Services Description Language (WSDL).
---The Service Requester is the business that requires a certain business function to be
fulfilled. From an architectural perspective, this is the application that is looking for
(queries the service registry) and then binds to and invokes the service. The requester
has to find the service before invoking it - this process of discovery involves accessing a
directory where the services are published. The access occurs through a set of
standard APIs defined in the UDDI standard. UDDI stands for Universal Description,
Discovery and Integration specification.

8. Extensible Markup Language -1
XML stands for EXtensible Markup Language.
XML is a markup language much like HTML.
The prefect choice for enabling cross-platform data communication in Web Services.

9. Extensible Markup Language -2
XML was designed to describe data.
XML tags are not predefined. You must define your own tags.
Processes XML messages framed using SOAP
Describes its messages using XML Schema
You can describe your message with XML in a machine readable way that is also human
readable. The data is structured and the meaning is embedded in the data itself. This is
core to building flexible architectures that deal with a wide range of different systems.

10. Simple Object Access Protocol
Based on XML
A simple markup language for describing messages between applications.
Mainly transferred via HTTP.

11. SOAP - Characteristics
Extensibility – security and WS-routing, ...
Neutrality - SOAP can be used over any transport protocol such as HTTP, SMTP or even TCP.
Independency - SOAP allows for any programming model.

12. SOAP - Building Blocks
A required Envelope element that identifies the XML document as a SOAP message.
An optional Header element that contains header information.
A required Body element that contains call and response information.
An optional Fault element that provides information about errors that occurred while processing the message.

13. SOAP – Request <?xml version="1.0"?> <soap:Envelope
xmlns:soap=" soap:encodingStyle=
<soap:Body xmlns:m="  
  <m:GetBazaarPrice>
<m:Type>Shirt</m:Type>    
 </m:GetBazaarPrice>
</soap:Body>
</soap:Envelope>

14. Soap - Response <?xml version="1.0"?>
<soap:Envelope xmlns:soap=" soap:encodingStyle="
<soap:Body xmlns:m="
<m:GetBazaarPriceResponse>
<m:Price>34.5</m:Price>
</m:GetBazaarPriceResponse>
</soap:Body>
</soap:Envelope>

15. WSDL Stands for Web Services Description Language. Based on XML.
WSDL specifies what a request message and a response message must contain. A contract between the XML Web service and the client ...
In addition to describing message contents, it defines where the service is available and what communications protocol can be used to invoke it.

16. WSDL - Primary Elements
PortType - Defines the abstract interface to the Service. Associated with one or more operations.
Message - Defines the information exchanged at the time an operation is executed (input and output). Made of one or more parts.
Part – Elemental piece of information in a message (an individual parameter or return value)
Types - The data types used by the web service.
Binding - The communication protocols used by the web service
Port – Identifies the actual location of the service (a URL, a Java class, etc..)

17. WSDL - Example <message name="GetBazaarPriceRequest">
<part name=“" type="xs:string"/>
</message>
<message name="GetBazaarPriceResponse">
<part name="value" type="xs:string"/>
<portType name=“BazaarsRates"> <operation name=“GetBazaarPrice"> <input message=“GetBazaarPriceRequest"/> <output message=“GetBazaarPriceResponse"/> </operation> </portType>

18. WSDL & OO
Example: a service implemented by a Java class could define one or more operations.
Operations would map to individual Java methods, implemented by the class.
Messages would map to the return types of the methods, or to their parameter list.
Parts would map to the elemental data in the parameter list or the return values.

19. UDDI

20. Service Oriented Architecture

21. Service Oriented Architecture -2
An approach for building distributed systems that deliver application functionality as services to either end-user applications or other services
The minimum requirements of an SOA are:
– Services
– Enterprise service bus (ESB)
– Service directory: An organization-level WSDL repository
– Internet gateway: Enables internal services to be exposed to the Internet

22. Value of SOA Build once, use often Interface by contract
One place to make one change
Lower development, operations and maintenance costs
Interface by contract
Loosely couples requestor and provider so each can vary independently
Integration is explicitly defined and so better understood, at the application and Enterprise level
Simplified, agreed, defined data and process flows