Introduction to web service especially in asp .net
A Web service is a class that allows its methods to be called by methods on other machines via common data formats and protocols, such as XML and HTTP. In .NET, the over-the-network method calls are commonly implemented through the Simple Object Access Protocol (SOAP), an XML-based protocol describing how to mark up requests and responses so that they can be transferred via protocols such as HTTP. Using SOAP, applications represent and transmit data in a standardized XML-based format.
A Web service is a software component stored on one machine that can be accessed by an application (or other software component) on another machine over a network. The machine on which the Web service resides is referred to as a remote machine. The application (i.e., the client) that accesses the Web service sends a method call over a network to the remote machine, which processes the call and returns a response over the network to the application.
Methods in a Web service are invoked through a Remote Procedure Call (RPC). These methods, which are marked with the WebMethod attribute, are often referred to as Web service methods or simply Web methods. Declaring a method with attribute WebMethod makes the method accessible to other classes through RPCs and is known as exposing a Web method.
Web services have important implications for business-to-business (B2B) transactions. They enable businesses to conduct transactions via standardized, widely available Web services rather than relying on proprietary applications. Web services and SOAP are platform and language independent, so companies can collaborate via Web services without worrying about the compatibility of their hardware, software and communications technologies.
Web services are not the best solution for certain performance-intensive applications, because applications that invoke Web services experience network delays. Also, data transfers are typically larger because data is transmitted in text-based XML formats.
Introduction to WebMethods in ASP .NET
Methods of a class that implement a Web service do not automatically have the ability to receive Web service requests and send back responses, but with Web services created using ASP.NET, it is very simple to add that capability. Apply a WebMethod attribute to public methods. Methods of a Web service class that can be communicated with over the Web are called Web service methods.
Web service methods are a key part of the messaging infrastructure employed by Web services. That is, a client and a Web service communicate using messages, specifically SOAP messages, by default. Clients send a SOAP request to a Web service and a Web service method typically returns a SOAP response. Web services define the type of messages they accept using operations, as defined by Web Services Description Language (WSDL). These operations correlate to each of the Web service methods within a Web service.
Even though each of these Web service methods are defined in ASP.NET using a method of a class, it is important to realize that the data that is eventually communicated over the network must be serialized into XML. As such, it is important to remember that Web services are not a replacement for DCOM, but rather a messaging infrastructure for communicating across platforms using industry standards.
Attaching the WebMethod attribute to a Public method indicates that you want the method exposed as part of the XML Web service. The WebMethod attribute tells .NET that a particular public method should be exposed as a web-callable method. The WebMethod attribute has six associated properties to document and change the behavior of your web method. They are:
Description
MessageName
EnableSession
CacheDuration
TransactionOption
BufferResponse
The first two properties are used to document a web method, while the others affect its behavior.
SOAP in .NET Web Services
The Simple Object Access Protocol (SOAP) is a platform-independent protocol that uses XML to make remote procedure calls.
Each request and response is packaged in a SOAP message containing the information that a Web service requires to process the message.
SOAP supports an extensive set of types like the primitive types, DataSet, DateTime, XmlNode and others. SOAP can also transmit arrays of these types and objects of user-defined types.
When a program invokes a Web method, the request and all relevant information are packaged in a SOAP message and sent to the server on which the Web service resides.
A Web service receives a SOAP message and parses its contents (contained in a SOAP envelope) to determine the method that the client wishes to execute and the method's arguments.
After a Web service parses a SOAP message, the proper method is called and the response is sent back to the client in another SOAP message. The client parses the response to retrieve the result.
User Defined Types in Web Services
It is possible to process user-defined types (also known as custom types) in a Web service. These types can be passed to or returned from Web methods. Web service clients also can use these user-defined types, because the proxy class created for the client contains these type definitions
Custom types that are sent to or from a Web service are serialized, enabling them to be passed in XML format. This process is referred to as XML serialization.
Classes that are used to specify Web method return types and parameter types must provide a public default or parameterless constructor. Properties and instance variables that should be serialized in XML format must be declared public. Properties that should be serialized must provide both get and set accessors. Read-only properties are not serialized. Data that is not serialized simply receives its default value when an object of the class is deserialized.
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