Windows Workflow Foundation (WF) is a technology that was first introduced in .NET Framework 3.0. WF consists of a programming model, a workflow runtime engine, workflow designer, a rules engine, and tools to quickly build workflow-based applications on Windows. WF facilitates the separation between the business process code and the actual implementation code.

State is quite an innovative concept in Web development because it eliminates the drawback of losing state data due to reloading of a Web page. By using states in a Web application, you can preserve the state of the application either at the server or client end. The state of a Web application helps you to store the runtime changes that have been made to the Web application. For example, as already described earlier, a change in the data source of the Web application might be initiated by a user when he/she selects and saves some products in the shopping cart.

If you are not using states, these changes are discarded and are not saved. You may think that the whole concept of storing states is optional. However, under certain circumstances, using states with applications is imperative. For example, it is necessary to store states for Web applications, such as an e-commerce shopping site or an Intranet site of a company, to keep track of the requests of the users for the items they have selected on the shopping site or the days requested for vacation on the Intranet site.

Validation controls are responsible to validate the data of an input control. Whenever you provide any input to an application, it performs the validation and displays an error message to user, in case the validation fails.

ASP.NET 4.0 contains the following six types of validation controls:

   => CompareValidator - Performs a comparison between the values contained in two controls.
   => CustomValidator - Writes your own method to perform extra validation.
   => RangeValidator- Checks value according to the range of value.
   => RegularExpressionValidator - Ensures that input is according to the specified pattern or not.
   =>  RequiredFieldValidator - Checks either a control is empty or not.
   => ValidationSummary - Displays a summary of all validation error in a central location.

You can use the System.Net.Mail.MailMessage and the System.Net.Mail.SmtpMail classes to send an email in your Web pages. In order to send an email through your mail server, you need to create an object of the SmtpClient class and set the server name, port, and credentials.

The App_Code folder is automatically present in the project. It stores the files, such as classes, typed data set, text files, and reports. If this folder is not available in the application, you can add this folder. One of the important features of the App_Code folder is that only one dll is created for the complete folder, irrespective of how many files it contains.

DLR is a runtime environment that allows you to integrate dynamic languages with the Common Language Runtime (CLR) by adding a set of services, such as expression trees, call site caching, and dynamic object interoperability to the CLR.

The System.Dynamic and System.Runtime.CompilerServices namespaces are used to hold the classes for DLR. It also provides dynamic features to statically-typed languages, such as C# and Visual Basic to enable their interoperation with dynamic languages.

One of the major component of ADO.NET is the DataSet object, which always remains disconnected from the database and reduces the load on the database.

ADO.NET is a very important feature of .NET Framework, which is used to work with data that is stored in structured data sources, such as databases and XML files. The following are some of the important features of ADO.NET:

 =>   Contains a number of classes that provide you with various methods and attributes to manage the communication between your application and data source.

 =>   Enables you to access different data sources, such as Microsoft SQL Server, and XML, as per your requirements.

 =>   Provides a rich set of features, such as connection and commands that can be used to develop robust and highly efficient data services in .NET applications.

 =>   Provides various data providers that are specific to databases produced by various vendors. For example, ADO.NET has a separate provider to access data from Oracle databases; whereas, another provider is used to access data from SQL databases.