Advantages of .Net Web Services

Web Services are supported on a wide range of platforms.

Web services may extend its interface and add new methods without affecting the clients as long as they still provide the old methods and parameters.

• A client makes a request to a web service, the web service returns the result, and the connection is closed. There is no permanent connection. This makes it easy to scale up and support many clients at a time.
• Firewalls can pose a challenge for distributed object technologies. The only thing that almost always gets through firewalls is HTTP traffic on ports 80 and 443. Because web services use HTTP, they can pass through firewalls without explicit configuration.

Explain in brief Web Service Standards.

Following are the standards used by web services:

WSDL
WSDL is used to create interface definition for a web services. It describes all about methods to the client, i.e. methods available in a web service, their parameters and return values.

SOAP

SOAP, Simple Object Access Protocol is a communication protocol, a way to structure data, based on XML. The web services use SOAP message format to encode information before sending.

HTTP
The SOAP message format in web services uses HTTP as communication protocol, i.e. SOAP messages are sent over HTTP channels.

DISCO
It is used to create discovery documents that provide links to multiple web service endpoints. The DISCO standard creates a single file that groups a list of related web services. A company can publish a DISCO file on its server that contains links to all the web services it provides.

UDDI
A standard for creating business registries that catalog companies, the web services they provide, and the corresponding URLs for their WSDL contracts.

Define the specifications that help in the discovery of a web service.

DISCO

DISCO, an abbreviation of discovery, is a file that groups together a list of related web services. A company that offers web services publishes a DISCO file on its server that has links of all the web services it provides. The client requests this file to see all the available web services. This standard is useful when client already know about a company that offers web services. You can also use DISCO standard while working in local network. It is not helpful to find all web services over the internet.

UDDI

UDDI (Universal Description, Discovery, and Integration) offers centralized directory for web services over the internet. It hosts web services from different companies and can be used by the clients to find web services of their specific need. To make web services shared publicly, they have to be published in UDDI.

What are the data types supported by Web Services?

.Net web services are built on XML-based standards for exchanging data. This means .NET web services can support only those data types that can be recognized by the XML schema standard. There are many proprietary .Net objects such as FileSteam, Eventlog etc. are not supported in the web services. These data types are .Net specific types that are not universally recognized, i.e. .Net specific only.

You can even exchange custom objects using .Net web services. The only limitation is that only public data members are transmitted, and all public members and properties must use one of the other supported data types.

You can use DataSet and DataTable to return information from database but can't use other ADO.NET objects such as DataColumns and DataRows.

.Net offers a distributed technology called .Net remoting that can plays around wide range of .Net specific data type. But unfortunately, .Net remoting doesn't support client other than .Net.

Testing and consuming a .Net web service.

Testing a Web Service

.NET has a test web page that ASP.NET uses automatically when you request the URL of an .asmx file in a browser. This page uses reflection to read and show information about the web services, such as the names of the methods it provides.

Consuming a Web Service

Web services are built on XML standard. So, a client needs to equip itself to understand XML-based message in order to exchange messages. The .Net framework provides proxy component that enable clients to interact with web services. The proxy has all necessary information that can be utilized by the client application to share data with web services.

The proxy class wraps the calls to the web service's methods. It generates SOAP message format and manages the transmission of the messages over the network (using HTTP). When it receives the response message, it converts the results back to the corresponding .NET data types.

You can create a proxy class in .NET in two ways:

By using wsdl.exe command-line tool
By using Visual Studio web reference feature