Understanding Web Service

Web Service

- a software system designed to support interoperable machine-to-machine interaction over a network.
- makes software functionality available over the Internet so that programs like PHP, ASP, JSP, JavaBeans, the COM object, and all our other favorite widgets can make a request to a program running on another server (a web service) and use that program’s response in a website, WAP service, or other application.
- describes a standardized way of integrating Web-based applications using the XML, SOAP, WSDL and UDDI open standards over an Internet protocol backbone.

2 Types of Web Service

1. SOAP (Simple Object Access Protocol)
   - a lightweight XML-based messaging protocol used to encode the information in Web service request and response messages before sending them over a network.
   - SOAP messages are formatted in XML and are typically sent using HTTP but can be also transported using a variety of Internet protocols, including SMTP and MIME.
   - older type, successor of XML-RPC
   - uses JAX-WS specification
2. REST
   - is simpler and more light weighted than SOAP
   - can send and receive data as JSON, XML or even plain text
   - uses JAX-RS specification

Related Terms

XML (Extensible Markup Language)
- a general-purpose specification for creating custom markup languages developed by the W3C.
- is a markup language much like HTML. A markup language is a mechanism to identify structures in a document.
- allows designers to create their own customized tags, enabling the definition, transmission, validation, and interpretation of data between applications and between organizations.

WSDL (Web Services Description Language)
- an XML-formatted language used to describe a Web service's capabilities as collections of communication endpoints capable of exchanging messages. WSDL is the language that UDDI uses, developed jointly by Microsoft and IBM.
- describes the interface of Web services

UDDI (Universal Description, Discovery and Integration)
- it is a Web-based distributed directory that enables businesses to list themselves on the Internet and discover each other, similar to a traditional phone book's yellow and white pages.

SEI (Service Endpoint Interface)
- is a Java interface class that defines the methods to be exposed as a Web service
- coverts the web service call including the (Java, C++, etc.) objects to a SOAP message

Protocol
- is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, semantics, and synchronization of communication. Protocols may be implemented by hardware, software, or a combination of the two.

References:
http://www.alistapart.com/articles/webservices
http://en.wikipedia.org
http://www.webopedia.com/TERM/W/Web_services.html
http://www.webopedia.com/DidYouKnow/Computer_Science/2005/web_services.asp
http://www.ibm.com/developerworks/library/ws-intwsdl
http://www.ibm.com/developerworks/library/ws-intwsdl2