WebService 学习笔记一

1.1 What Are Web Services?
A web service is a piece of business logic, located somewhere on the Internet, that
accessible through standard-based Internet protocols such as HTTP or SMTP. Using a w
service could be as simple as logging into a site or as complex as facilitating a mul
organization business negotiation.

A web service has special behavioral characteris

1)XML-based
2)Loosely coupled :
A consumer of a web service is not tied to that web service directly; the web service
interface can change over time without compromising the client's ability to interact
with the service
3)Coarse-grained:
Web services technology provides a natural way of defining coarse-grained services that access the right amount
of business logic.
4)Ability to be synchronous or asynchronous
In synchronous invocations, the client blocks and waits for the service to complete its
operation before continuing.
Asynchronous operations allow a client to invoke a service and then execute other functions.

Asynchronous capability is a key factor in enabling loosely coupled systems.
5) Supports Remote Procedure Calls (RPCs)
6)Supports document exchange
Web services support the transparent exchange of documents to facilitate business integration.


1.1.1 The Major Web Services Technologies

1）Simple Object Access Protocol (SOAP) :

SOAP provides a standard packaging structure for transporting XML documents over
a variety of standard Internet technologies, including SMTP, HTTP, and FTP. It also
defines encoding and binding standards for encoding non-XML RPC invocations in
XML for transport. SOAP provides a simple structure for doing RPC: document
exchange. By having a standard transport mechanism, heterogeneous clients and
servers can suddenly become interoperable. .NET clients can invoke EJBs exposed
through SOAP, and Java clients can invoke .NET Components exposed through
SOAP.

2）Web Service Description Language (WSDL)：

WSDL is an XML technology that describes the interface of a web service in a
standardized way. WSDL standardizes how a web service represents the input and
output parameters of an invocation externally, the function's structure, the nature of
the invocation (in only, in/out, etc.), and the service's protocol binding. WSDL allows
disparate clients to automatically understand how to interact with a web service.

3）Universal Description, Discovery, and Integration (UDDI)

UDDI provides a worldwide registry of web services for advertisement, discovery, and
integration purposes. Business analysts and technologists use UDDI to discover
available web services by searching for names, identifiers, categories, or the
specifications implemented by the web service. UDDI provides a structure for
representing businesses, business relationships, web services, specification metadata,
and web service access points

三种技术的交互:
an application acting in the role of a web services client needs to locate another
application or a piece of business logic located somewhere on the network. The client queries
a UDDI registry for the service either by name, category, identifier, or specification
supported. Once located, the client obtains information about the location of a WSDL
document from the UDDI registry. The WSDL document contains information about how to
contact the web service and the format of request messages in XML schema. The client
creates a SOAP message in accordance with the XML schema found in the WSDL and sends
a request to the host (where the service is).