What Is an ASP File? Files created with Active Server Pages have the extension .ASP. This story is an example; take a look at the address above. With ASP files, you can activate your Web site using any combination of HTML, scripting such as JavaScript or Visual Basic?

Is It Hard to Use? I don't know about you, but whenever people start talking about doing things on the server, I start to get nervous. I think a lot about threading issues, synchronization, and generally stuff without a user interface. I assume it's going to be hard to do. Well, using ASP is about as easy as anything I've come across in years.

Aw, Mom. Not Another Object Model! I really hate doing this to you, but I'm going to have to use that overused and overcomplex term "object model" again. Here's how it works. When a browser requests an ASP file from your Web server, your Web server calls Active Server Pages to read through the ASP file, executing any of the commands contained within and sending the resulting HTML page to the browser.

I really hate doing this to you, but I'm going to have to use that overused and overcomplex term "object model" again. Here's how it works. When a browser requests an ASP file from your Web server, your Web server calls Active Server Pages to read through the ASP file, executing any of the commands contained within and sending the resulting HTML page to the browser. An ASP file can contain any combination of HTML, script, or commands. The script can assign values to variables, request information from the server, or combine any set of commands into procedures.

ASP uses the delimiters (better known to you and me as "thing-a-ma-bobs that specify the beginning and end") "<%" and "%>" to enclose script commands. For example, the code below sets the value of the variable "MyFavTVShow" in the user cookie to "I Dream of Jeannie."

The scripting languages supported by ASP in turn support use of the If-Then-Else construct (something that will undoubtedly warm the hearts of all coders out there). Finally, you can embed some real logic into your HTML. For example, the following code from the IIS documentation shows how you can set the greeting shown based upon the time of day.

I'm sure that you can think of something more interesting for your Web site¡ªI'd hate to have to come up with all of the clever ideas.

ASP includes five standard objects for global use:

• Request ¡ªto get information from the user
• Response ¡ªto send information to the user
• Server ¡ªto control the Internet Information Server
• Session ¡ªto store information about and change settings for the user's current Web-server session
• Application ¡ªto share application-level information and control settings for the lifetime of the application

The Request and Response objects contain collections (bits of information that are accessed in the same way). Objects use methods to do some type of procedure (if you know any object-oriented programming language, you know already what a method is) and properties to store any of the object's attributes (such as color, font, or size).

The Request object is used to get information from the user that is passed along in an HTTP request. As I mentioned earlier, the Request and Response objects support collections:

• ClientCertificate ¡ªto get the certification fields from the request issued by the Web browser. The fields that you can request are specified in the X.509 standard
• QueryString ¡ªto get text such as a name, such as my favorite TV sitcom above
• Form ¡ªto get data from an HTML form
• Cookies ¡ªto get the value of application-defined cookie
• ServerVariables ¡ªto get HTTP information such as the server name

The Response object is used to send information to the user. The Response object supports only Cookies as a collection (to set cookie values). The Response object also supports a number of properties and methods. Properties currently supported are:

• Buffer ¡ªset to buffer page output at the server. When this is set to true, the server will not send a response until all of the server scripts on the current page have been processed, or until the Flush or End method has been called.
• ContentType ¡ªto set the type of content (i.e: text/HTML, Excel, etc.)
• Expires ¡ªsets the expiration (when the data in the user's cache for this Web page is considered invalid) based on minutes (i.e.: expires in 10 minutes).
• ExpiresAbsolute ¡ªallows you to set the expiration date to an absolute date and time.
• Status ¡ªreturns the status line (defined in the HTTP specification for the server).

The following methods are supported by the Response object:

• AddHeader ¡ªAdds an HTML header with a specified value
• AppendToLog ¡ªAppends a string to the end of the Web server log file
• BinaryWrite ¡ªwrites binary data (i.e, Excel spreadsheet data)
• Clear ¡ªclears any buffered HTML output.
• End ¡ªstops processing of the script.
• Flush --sends all of the information in the buffer.
• Redirect ¡ªto redirect the user to a different URL
• Write ¡ªto write into the HTML stream. This can be done by using the construct

or the shortcut command

<%="hello"%>

The Server object

The Server object supports one property, ScriptTimeout, which allows you to set the value for when the script processing will time out, and the following methods:

• CreateObject ¡ªto create an instance of a server component. This component can be any component that you have installed on your server (such as an ActiveX ).
• HTMLEncode ¡ªto encode the specified string in HTML.
• MapPath ¡ªto map the current virtual path to a physical directory structure. You can then pass that path to a component that creates the specified directory or file on the server.
• URLEncode ¡ªapplies URL encoding to a specified string.

The Session object is used to store information about the current user's Web-server session. Variables stored with this object exist as long as the user's session is active, even if more than one application is used. This object supports one method, Abandon , which (believe it or not!) abandons the current Web-server session, destroying any objects, and supports two properties, SessionID , containing the identifier for the current session, and Timeout , specifying a time-out value for the session. One thing to bear in mind about the session identifier: It's not a GUID. It's only good as long as the current Web-server session is running. If you shut down the Web-server service, the identifiers will start all over again. So don't use it to create logon IDs, or you'll have a bunch of duplicates and one heck of a headache.

The Application object can store information that persists for the entire lifetime of an application (a group of pages with a common root). Generally, this is the whole time that the IIS server is running. This makes it a great place to store information that has to exist for more than one user (such as a page counter). The downside of this is that since this object isn't created anew for each user, errors that may not show up when the code is called once may show up when it is called 10,000 times in a row. In addition, because the Application object is shared by all the users, threading can be a nightmare to implement.