What are VSDISCO files ?

VSDISCO files are DISCO files that enable dynamic discovery of Web Services. ASP.NET links the VSDISCO to a HTTP handler that scans the host directory and sub-directories for ASMX and DISCO files and returns a dynamically generated DISCO document.

What is Webservices

Web services are programmable business logic components that provide access to functionality through the Internet. Standard protocols like HTTP can be used to access them. Web services are based on the Simple Object Access Protocol (SOAP). Web services are given the .asmx extension .We have to use the standard to wrap up a call to a Web service is HTTP with SOAP.

What is Sealed class ?

A class can be made sealed in c# using the sealed keyword. Sealed means that the class cant be inhereted. You can extend this functionality to the individual methods as well. In case you want a class to be inhereted, excluding one of its methods, just make that particular method sealed.

What namespaces are imported by default in ASPX files

The following namespaces are imported by default. Other namespaces must be imported manually using @ Import directives.
· System
· System.Collections
· System.Collections.Specialized
· System.Configuration
· System.Text
· System.Text.RegularExpressions
· System.Web
· System.Web.Caching
· System.Web.Security
· System.Web.SessionState
· System.Web.UI
· System.Web.UI.HtmlControls System.Web.UI.WebControls

ViewState

Each control on a Web Forms page, including the page itself, has a ViewState property that it inherits from the base Control class. View state is used by the ASP.NET page framework to automatically save the values of the page and of each control just prior to rendering to the page. When the page is posted, one of the first tasks performed by page processing is to restore view state.
You can use the ViewState property to save your values independent of control state between round trips to the server. The ViewState property is stored in the page in a hidden form field

Difference Between ViewState and SessionState

ViewState persist the values of controls of particular page in the client (browser) when post back operation done. When user requests another page previous page data no longer available.

SessionState persist the data of particular user in the server. This data available till user close the browser or session time completes.

Metadata and Manifest

Manifest describes the assembly itself. Assembly name, version, culture, strong name, list of files, type reference and reference assembly. While Metadata describes contents within the assembly like classes, namespaces, interfaces, scope, properties, methods and their parameters etc.