Rs.15

It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.

Proactive Update:
The updates that are applied to database before it becomes effective in real world .
Retroactive Update:
The updates that are applied to database after it becomes effective in real world .
Simulatneous Update:
the updates that are applied to database at the same time when it becomes effective in real world .

Rs.15

Web forms are very similar to traditional HTML forms. The difference is that Web forms are server-based, meaning you create the user elements on the server. The server has complete knowledge of what the interface looks like, what it can do what data it expects, and so on. Web forms pages are divided into two parts: the visual elements and the accompanying UI logic. These two components are completely separate from each other conceptually, and they can be physically located anywhere you want. Typically, both parts are contained within one .aspx file. The System.Web.UI namescape defines classes and interfaces used in constructing nd rendering elements on a Web form. The most important class in the System.Web.UI is the Control class which defines the properties, methods and events that are common in all server controls in the WebForm framework. Another important class in this namespace is Page which is a derivative of the Control Class. All ASP.NET web pages are instances of derivatives of the Page Class. To have an extensible framework, the System.Web.UI namespace also includes the UserControl class which is similar to Page class except that it is mainly used as the base class for user controls.