INTRODUCTION TO ASP.NET

Posted Date: 21 May 2008 Resource Type: Articles/Knowledge Sharing Category: Computer & Technology

Posted By: mohit Member Level: Gold
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Introduction to ASP.NET:
ASP.NET is a technology that allows us to build and control dynamic Web pages easily. It also provides many enhancements to take advantage of new technology as we can interact with databases, personalize Web pages for visitors, display page on mobile devices (such as cell phones), and even build an entire e-commerce site from scratch.
Previously internet works on request/response model that is an integral part of client/server model. Although this is a marvelous way of communicate and distribute information, it's rather simple and static. When the process is over, once client receives the requesting page from the server the server has no idea what the client is doing unless it makes another request.
There is another model for communicating between server and clients, known as event-driven model.ASP.NET work on this model, it detects action and responds to them i.e. the server waits around for something to happen on the client. Once it does, the server takes action and performs some piece of functionality. Of course, a Web, server can not know what you are thinking, but it can respond to your actions. If you type some text on Web page, the server responds to it. If you click an image, the server responds.

Responses

Author: mohit 21 May 2008

Member Level: Gold Points : 2

COMPARISON OF ASP AND ASP.NET:

? Classic ASP was built on the top of the Windows operating system and IIS (Internet Information Server). It was always a separate entity, and therefore its functionality was limited. ASP.NET, on the other hand, is an integral part of the system under the .NET Framework. It shares many 9f the same objects that traditional applications would use and all .NET objects available for ASP. NET consumption.
? Instead of being limited to six inherent objects in ASP, ASP.NET has a plethora of useful components it can build form.
? ASP also made it abundantly clear that client and server were two separate entities, Whereas ASP. NET ties together the client and the server through clever use of server-side and client-side code, all invisible to the developer.
? ASP.NET code is compiled, whereas classic ASP used interpreted scripting languages. Using compiled code means an automatic boost in performance over ASP applications.
? In classic ASP, nearly all of the code was executed in code render blocks (that is, inside <%...%> tags). In ASP.NET, this type of code isn’t compiled and isn’t recommended for frequent use. Instead, you use the code declaration blocks, which are compiled and provide better performance.

Author: mohit 21 May 2008

Member Level: Gold Points : 2

Following are some of the significant new features of ASP.NET:
? ASP.NET uses compiled code written in Common Language Runtime languages such as Visual Basic and C#. Unlike previous versions of Active Server Pages, this version does not use interpreted scripting languages such as VBScript.
? ASP.NET pages are built out of server-side controls. Web server controls enable you to represent and program against Hypertext Markup Language (HTML) elements using an intuitive object model.
? ASP.NET includes a new technology called Web Services. You can use Web Services to access methods and properties and transfer database data across the Internet.
? ASP.NET is part of Microsoft's .NET Framework. You can access thousands of .NET classes in your code that enable you to perform such wondrously diverse tasks as generating images on-the-fly and saving an array to a file.
? ASP.NET includes page and data caching mechanisms that enable you to easily and dramatically improve the performance of your Web site.

Author: mohit 21 May 2008

Member Level: Gold Points : 2

What is ASP.NET?
This may seem like a relatively simple question, but I assure you that it's not.
Because ASP.NET is part of the .NET framework, it is available on any server with the framework
installed. In other words, it's not an add-on anymore; ASP has become legitimate. ASP.NET is
implemented in an assembly that exposes classes and objects that perform predetermined specific
tasks. If you are familiar with "classic" ASP (the versions of ASP that preceded .NET), you'll find that
your approach to programming in ASP.NET is somewhat different, but the concepts behind building a
Web application are much the same. If you're not familiar with classic ASP, so much the better— you
won't have as much information to forget!
ASP.NET programs are centralized applications hosted on one or more Web servers that respond
dynamically to client requests. The responses are dynamic because ASP.NET intercepts requests for
pages with specific extensions, for example .aspx or .ascx, and hands off the responsibility for
answering those requests to just-in-time (JIT) compiled code files that can build a response on-the-fly.
(web.config and machine.config) files, Web Services (ASMX) files, and Web Forms (ASPX) files.
The server doesn't "serve" any of these file types— it returns the appropriate content type to the client.
The configuration file types contain initialization and settings for a specific application or portion of an
application. Another configuration file, called machine.web, contains machine-level initialization and
settings. The server ignores requests for Web files, because serving them might constitute a security
breach.
This book concentrates on Web Forms and Web Services. Client requests for those file types cause the
server to load, parse, and execute code to return a dynamic response. For Web Forms, the response
usually consists of HTML or WML. For Web Services, the server typically creates a Simple Object
Access Protocol (SOAP) response. While SOAP requests are inherently stateless and can thus execute
immediately, Web Forms are stateful by default. Web Forms maintain state by round-tripping user
interface and other persistent values between the client and the server automatically for each request. It is
possible (but not the default) to take advantage of ASP.NET's state maintenance architecture from a
Web Service, but for performance reasons, you should generally avoid doing so.
Both Web Forms and Web Services requests can take advantage of ASP.NET's integrated security and
data access through ADO.NET and can run code that uses system services to construct the response.
The major difference between a static request and a dynamic request is that a typical Web request
references a static file. The server reads the file and responds with the contents of the requested file.
With ASP.NET there's no such limitation. You don't have to respond with an existing file— you can
respond to a request with anything you like, including dynamically created HTML, Extensible Markup
Language (XML), graphics, raw text, or binary data— anything. Capability, by itself, is nothing new—
you've been able to create CGI programs, JavaServer Pages, classic ASP pages, ColdFusion, and Net-
Objects Fusion pages for quite some time. All these technologies give you the capability to respond to
an HTTP request dynamically. So what are the differences?
n Unlike classic ASP, ASP.NET uses .NET languages. Therefore, you have access to the full power
of any .NET assembly or class in exactly the same way as you do from any other Windows
application written in C#. In this sense, ASP.NET is similar to early compiled CGI programs, but with
CGI, a separate copy of the program had to be loaded and executed for each request. ASP.NET
code exists in multithreaded JIT-compiled DLL assemblies, which can be loaded on demand. Once
loaded, the ASP.NET DLLs can service multiple requests from a single in-memory copy.
n ASP.NET supports all the .NET languages (currently C#, C++, VB.NET, and JScript, but there are
well over 20 different languages in various stages of development or deployment for .NET), so you
will eventually be able to write Web applications in your choice of almost any modern programming
language. In addition, there are open source groups working with Intel and Hewlett-Packard to
support .NET on various flavors of Unix and Linux. JavaServer Pages support only Java, but
because Java now has a wide support base, that's not much of a limitation. Java Servlets are more
like ASP.NET but offer little support for state maintenance, Web Services, or XML. In addition, no
Java design environment competes in features and quality to Visual Studio.
n Classic ASP supported several scripting languages, although in practice, VBScript and JScript were
by far the most prevalent. Although the scripting languages you could use with classic ASP were
untyped, interpreted, and not particularly powerful, you could extend ASP's basic functionality by
writing DLLs in any COM-compliant language. Another ASP.NET competitor, ColdFusion, uses
ColdFusion Markup Language (CFML) tags, which have a powerful but limited set of capabilities;
however, you can extend CFML with custom programming in C++ or Java.
n Microsoft was able to draw on millions of hours of developer experience with classic ASP, so in
addition to huge increases in speed and power, ASP.NET provides substantial development
improvements, such as seamless server-to-client debugging, automatic validation of form data, and
a programming model very similar to that of a Windows application.

Author: mohit 21 May 2008

Member Level: Gold Points : 2

Framework for Processing HTTP Requests

Microsoft's Web server, Internet Information Server (IIS), handles HTTP requests by handing off the
request to the appropriate module based on the type of file requested. Note that IIS responds with one
of only a few possible actions when it receives a request.
Respond with the File's Contents The server locates and reads the requested file's
contents and then streams the contents back to the requester. The server responds in this
manner to .htm and .html file requests, as well as to all requests that have no
associated application type— for example, EXE files.
Respond by Handing Off the Request The server hands off requests for files that end
in .asp to the classic ASP processor and files that end in .aspx, .ascx, or .asmx to the
ASP.NET processor.
Respond with an Error IIS responds with a customizable error message when a
requested file does not exist, when the requesting client has insufficient permissions to
authenticate or access the resource, or when an error occurs during processing.
Using the Internet Services Manager, you can change IIS's response to any particular file extension. For
example, you could have the ASP.NET engine handle all requests for files with .htm or .html
extensions, or you can create your own extensions and assign an action to them.

Author: mohit 21 May 2008

Member Level: Gold Points : 2

Author: mohit 21 May 2008

Member Level: Gold Points : 2

Why Do You Need ASP.NET?
The first computer languages were little more than mnemonics substituting for raw machine code
instructions, but as computers became more complex, each new language generation has supported an
increasing level of abstraction. Visual Basic, for example, abstracted user interface design and
construction into simple drag-and-drop operations (a model that VS.NET extends to all .NET-compliant
languages). For the first time, you could create a working Windows application with very little effort.
Similarly, when Web programming first became widespread, there were few tools to help programmers
write Web applications. To create a Web application, you initially had to write low-level socket
communications code. Over the years, the abstraction level has increased for Web programming as
well. First Common Gateway Interface (CGI) let you create executables that handled requests. Next, the
Internet Server API (ISAPI) and its counterpart NSAPI (Netscape Server API) let you intercept requests
and serve them from in-memory code components (DLLs), which was much faster. An ISAPI module, in
turn, could host a scripting engine, a combination that became the basis for classic ASP and proved to
be extremely popular with programmers. Microsoft extended the power of scripting language Web
programming in classic ASP by providing several "intrinsic" objects. These represented the request, the
server's response, the server itself, the user's session, and the "application." All together, they simplified
and automated the process of parsing and encrypting the request and response data and made it easier
to maintain global values and data for individual clients.
ASP.NET is the latest (and arguably the best) of these abstractions because it lets you work almost
exclusively with rich high-level classes and objects rather than directly with raw data. Without ASP.NET,
building a Web application is a chore. With ASP.NET, building a Web application is similar to building a
Win32 application.

Author: mohit 21 May 2008

Member Level: Gold Points : 2

WHATS NEW IN ASP.NET

Client Changes
ASP.NET lets you build Web-based applications that interact with pages displayed remotely. Originally,
classic ASP was designed to work with browsers, which at that time were capable of little more than
displaying data and images wrapped in HTML markup. While the integration hasn't changed, the clients
have changed dramatically. For example, modern browsers are much more capable than the version 3
browsers available when classic ASP was first developed. Not only can they display HTML and images,
they also support Cascading Style Sheets (CSS), Dynamic HTML (DHTML), XML (to varying degrees),
animations, complex image effects, vector graphics, sound, and video— and can run code, letting you
offload appropriate portions of your application's processing requirements from your server to the client.

Centralized Web-Based Applications
It's not only browsers that have changed. Centralized Web-based applications have garnered a huge
investment from companies that increasingly need to support mobile and remote clients. The cost of
supplying private network connectivity to such clients is prohibitive, yet the business advantages of
supporting such clients continue to rise. The only cost-effective way to supply and maintain corporate
applications to these mobile and remote workers is to uncouple them from the network and build the
applications to work over the public Internet via HTTP, WAP, and other advanced protocols. Therefore,
Web-based applications are no longer the exclusive purview of Webmasters and specialist developers;
they've become an integral part of the corporate IT operations.

Distributed Web-Based Applications
For all the advantages of centralized Web applications, they mostly ignore a huge reservoir of
processing power that exists on the client machines. Recently, a new breed of application has begun to
attract attention— the point-to-point program (often abbreviated as "P-to-P" or "P2P"). These programs
typically use XML to pass messages and content directly from one machine to another. Most current
implementations, such as Groove and Napster, use a centralized server as a directory service that helps
individuals or machines contact one another. Peer-to-peer applications are often called distributed
because the application runs at many points on the network simultaneously. In addition, the data used
by distributed applications is usually (but not necessarily) stored in multiple locations. Finally,
applications have begun to appear that run on multiple clients simultaneously, taking advantage of the
enormous amount of unused processing power that exists on the "edge" of the Web. Unlike standard
applications, no one machine has to have the entire application; instead, each client processes data as
requested and coordinated from a central server— in other words, the application uses the edge
machines as nothing more than an extra CPU.

Functional Interoperability
As the client transition from stand-alone applications to browser-based interfaces occurred, another
factor came into play: interoperability. IT departments have struggled with interoperability ever since
programming escaped the confines of the mainframe. As the number of computers and computing
devices within the business and entertainment worlds expanded, the problem grew. Today, computing is
no longer limited to full-size desktop machines or even laptops. Handheld and notepad computers,
telephones, and even pagers communicate with the Web servers and need to display data— sometimes
even display the same data or run the same application as a desktop box. Similarly, IT departments now
run critical applications on mainframes, minicomputers, and several different types of servers, from small
departmental servers to server farms that supply computing power to the entire enterprise and beyond.
These servers are made by different vendors and often run differing and incompatible operating
systems, yet companies often need to transport and consume data between the various machines,
databases, application tiers, and clients.
Companies have attacked the interoperability problem in several ways. They've tried limiting the
hardware and software— creating tight corporate standards for desktop, laptop, and handheld
computers. That approach hasn't worked very well— the industry changes too fast. They've tried and
discarded the thin-client network computer approach. Too little benefit, too late. They've tried implementing
Java as both the platform and the language— but performance issues, a lack of cooperation between
the major software suppliers, and the lack of commercial-quality software have— at least temporarily—
quelled that approach as well. Fortunately, a new interoperability standard has recently presented itself:

Extensible Markup Language (XML).
Standardization, Verifiability, and HTTP Affinity
XML provides a possible solution to some of these interoperability problems. XML is not a panacea, but
it does provide a standardized and verifiable text-based file format that can help ease the problems
involved in moving data from one server to another, as well as accommodate displaying identical data
on disparate clients. XML's standardization helps because the file format is universally recognized. XML
simplifies programming because it can verify, by using a document type definition (DTD) or schema, that
a file does indeed contain a specific type of content. Finally, XML's text-based format transfers very well
over a plain HTTP connection, which helps avoid problems with firewalls and malicious code.

Web Services
These attributes— standardization, verifiability, and HTTP affinity— led to a new use for ASP: creating
server-based code that delivers data without necessarily delivering HTML. In .NET, such pages are
called Web Services. You can think of a Web Service as a function call or as an object instantiation and
method call across the Web. Just as Web browsers and Web servers use a common protocol— HTTP—
to communicate across the network, a Web Service uses a common XML structure called Simple Object
Access Protocol (SOAP) to communicate with the calling application.

Author: mohit 21 May 2008

Member Level: Gold Points : 2

What Does ASP.NET Do?
What does ASP.NET do? Again, this is not a simple question. Classic ASP was limited to simple script
languages that could respond to requests but provided no intrinsic direct access to system services
other than those few required to read and respond to a request, such as writing output text. Although
you could extend classic ASP through commercial or custom-built COM components, the relatively high
overhead required to create COM objects and classic ASP's reliance on untyped interpreted scripting
languages limited system performance. In contrast, creating .NET framework objects requires very little
overhead, and ASP.NET lets you use fully object-oriented languages with seamless access to system
services. Therefore, I'll describe just the primary tasks that ASP.NET accomplishes now, and I'll fill in the
practical details in the remainder of this book.
Accepts Requests
All ASP.NET pages work essentially the same way. A client application makes an HTTP request to a
Web server using a URL. The Web server hands off the request to the ASP.NET processor, which
parses the URL and all data sent by the client into collections of named values. ASP.NET exposes these
values as properties of an object called the HttpRequest object, which is a member of the
System.Net assembly. An assembly is a collection of classes. Although an assembly can be a DLL, it
may consist of more than one DLL. Conversely, a single DLL may contain more than one assembly. For
now, think of an assembly as a group of related classes.
When a browser, or more properly a user agent, makes a request, it sends a string containing type and
version information along with the request. You can retrieve the HTTP_USER_AGENT string via the
HttpRequest object. For example, the following code fragment retrieves several items from the user
agent and writes them back to the client. An ASP.NET Web Form Page object exposes the Http-
Request with the shorter name Request that's familiar to classic ASP programmers.
Response.Write("UserAgent=" & Request.UserAgent & "
")
Response.Write("UserHostAddress=" & Request.UserHostAddress & "
")
Response.Write("UserHostName=" & Request.UserHostName & "
")
Builds Responses
Just as ASP.NET abstracts incoming data in the HttpRequest object, it provides a way to respond to
the request via the HttpResponse object. Abstracting responses in this manner has been so
successful that you'll find you need to know almost nothing about HTTP itself to use the HttpRequest
and HttpResponse objects.
Assists with State Maintenance
Unlike a stand-alone or standard client-server application, Web applications are "stateless," which
means that neither the client nor the server remembers each other after a complete request/response
cycle for a single page finishes. Each page requested is a complete and isolated transaction, which
works fine for browsing static HTML pages but is the single largest problem in constructing Web
applications.
Classic ASP introduced the idea of a session, which begins the first time a client requests any page in
your application. At that point, the ASP engine creates a unique cookie, which the browser then accepts
and returns to the server for each subsequent page request. ASP used the cookie value as a pointer
into data saved for that particular client in an object called the Session object. Unfortunately, because
the client data was stored in memory on a single server, this scheme did not scale well, nor was it faulttolerant.
If the Web server went down, the users lost the in-memory data.
ASP.NET uses much the same cookie scheme to identify specific clients, but the equivalent of the
Session object is now called the HttpSessionState object. ASP.NET addresses the sessionscalability
and data-vulnerability problems in classic ASP by separating state maintenance from the
ASP.NET engine. ASP.NET has a second server application, called the session server, to manage
session data. You can run the session server in or out of the IIS process on the same machine as your
Web server or out of process on a separate computer. Running it on a separate computer lets you
maintain a single session store across multiple Web servers. ASP.NET also adds the option to maintain
state in SQL Server, which increases fault tolerance in case the session server fails.

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