Active Server Pages
Emerging Technologies
Prepared for Cliff Layton
Michael D. Donahoe
Introduction
Active Server Pages or ASP is a specification designed by Mircosoft for a dynamically created web page with a .asp extension that utilizes Active X scripting. Most ASP pages are written using VB script a simpler version of Visual Basic code, but other languages have recently been incorporated such as Jscript – similar to Javascript, and more traditional languages such as C++, Perl, and CGI.. When a browser such as Internet Explorer or Netscape Navigator requests an ASP page the Web server generates a page with HTML code and sends it back to the user’s browser. This concept is commonly known as server-side scripting where the script is executed on the server side rather than the client or user’s side.
ASP is used in various ways to create dynamic and useful web sites and web applications. Visual effects can be added to a web page to help enhance the visitor’s experience by use of forms, changing of backgrounds, etc. These pages can be used to add a personal touch to a page by “remembering” the visitors name with the use of a cookie or by utilizing the most powerful tool of ASP to interface with a database. By connecting to a database user authentication can be performed which can tie together specific information in the database that relates to the user.
The example shown above is an ASP page that I wrote for our Quality Department at work. As you can see when the page is pulled up after I’ve logged in with a user name and password, it addresses me with a specialized greeting. This particular page is connected to a MS Access database which when I entered my user name and password, it stored that information into a cookie and then did a lookup in the database for a user name that matched the value in the cookie. It then cross referenced that information to what my actual first name was and returned that information back to the web page. Thus you’ll see “Welcome to the IQO Database” and then my first name, “Michael”. The page then goes further to access records in the database that apply to me. It searches for audit requests for me to do, then shows me the requests that I have accepted and still need to perform. This database is all web interfaced to the MS Access database. Through the use of ASP users are able to read, write, and view information in an HTML format to the database. It literally gives the complete power of a database to an HTML format. Also, it greatly enhances capabilities of the database. Whereas there are a limited number of users that can connect to a MS Access database at a single time, it isn’t the case by interfacing with ASP pages. Since the users are interfacing the MS Access database through the Web, this database can support virtually over 1,000 users at any given time. This simply because the ASP pages request the info one time, which takes milliseconds to download, then the ASP page does all the processing of the information before sending it to the users’ browser. The database itself does very little processing at all other than initially running the requested query.
History
Active
Server Pages 1.0 was released in 1996 to be used in conjunction with IIS
(Internet Information Server) on Windows NT web servers. Before the invention of ASP there was
CGI/Perl and PerlScript that processed information from and to web pages from
the server side. A CGI application could
only handle one CGI user at a time. If
20 people were to fill out and send information from a web forms on 20 separate
computers, then 20 copies of the CGI application had to be ran on the
server. This slowed down the server
quite considerably. Server APIs or
Application Programming Interfaces were then developed to allow multiple users
to a single web application.
Microsoft’s version of APIs are ISAPI, or Internet Server Application Programming Interface. ISAPI is more efficient than the traditional CGI interfaces. CGI, however, is very widespread, particularly on UNIX servers. Developments have recently been made to allow CGI to work in conjunction with ASP pages as well. Creating web sites with ISAPI was very time consuming and was very difficult to program, this made development very expensive to maintain. Active Server Pages then evolved which are easy to learn and are just as efficient as ISAPI.
Hypertext Markup Language
In order to understand ASP, some brief knowledge of how a web page is constructed must be known. Most web pages are written in HTML (hypertext markup language), which is processed by your web browser. The following is a very simple web page.
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To the right you will see a very
simple web page written in HTML that contains a picture, text, and a
link. If we were to view the source code for the web page by
right-clicking on the page and selecting 'view source' from the pop-up menu
you would see the HTML code displayed that is downloaded to the web
browser. The web browser displays the web page based upon the following
code or tags.
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This example of an HTML page is
very simple example of a common web page. When the address of the web
page is typed into the address bar, the page html code is downloaded directly
from the web server and then executed by the client-side web browser.
ASP in Action
The appearance of an Active Server Page is very similar to a standard HTML page. In fact, to the Web browser that receives the web page, there is no difference in the look; the difference is what can be obtained in the content. If the user was to view the source of an ASP page all they would see is the HTML code of the page combined with the HTML code written by the server-side scripts that exist in the page on the server. In other words, the user only can view the results of the scripts. If a user were able to see the ASP page on the server, you would be able to see embedded scripts within the HTML code of the web page that produces the information seen by the user.
Server-side scripts look a great deal like HTML tags. However, instead of tags starting and ending with lesser-than ( < ) and greater-than ( > ) brackets, they start with <% and end with %>. These are called opening and closing tags that tell the server to perform the function that’s inside of those tags before sending to the user. These tags and the scripts can be inserted anywhere within a Web page, even inside of HTML tags.
It is important to understand that when using ASP to process information to a web page that the charachteristics of what is displayed to the user are that of the server. In the example following I have created a web page that displays the day of the week, if a person were to create an ASP that displayed the current time, it would display the server’s time and not the user’s time. This could be confusing to some users depending on the use that are in different time zones than where the server is located.
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To the right is an example of the
same Web page that we used before only instead we've added a server-side
script within the HTML code to print the day of the week. The following is
the code for the ASP page: <html> <p>Today is <% =
WeekdayName(Weekday(Date)) %> </p> <p><img border="0" src="../../../Inetpub/wwwroot/iqo/bs01316_.gif" width="102"
height="186"></p> |
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This one line server-side script,
written with VBscript takes the server's date, determines the weekday as 5, and
then writes the weekday name of the fifth day of the week, which is Thursday.
If the client views the source of
the ASP from his or her web browser the result will only show the results of the
executed VBscript rather than the contents of the VBscript code.
<html
<head
<titleMy ASP Homepage</title
</head
<body
<pWelcome to my homepage. </p
<pToday is Thursday </p ß Result of
executed script.
<p<img border="0" src="bs01316_.gif" width="102"
height="186"</p
<pTo see my real homepage <a
href="http://www.mdonahoe.com"<click here></a</p
</body
</html
As seen above, rather than client being able to see
the VBscript that computes the day of the week, only the result will be
written, "Thursday" as if it were written directly into the HTML
code. Of course this is a very simplified example. Generally, more
complex code written in VBscript is utilized to interface with databases such
as online banking, compiled customer feedback from online survey forms, full
e-commerce websites that include purchasing, viewing based upon user
preferences, etc.
ASP.NET – The Latest Innovation in ASP
Technology
ASP.NET is the latest
version of ASP following ASP 3.0, sometimes currently referred to as ASP+. It is currently supported on Windows 2000 and
Windows XP with IIS installed.. However,
just as ASP 3.0 had aftermarket versions produced that ran on Linux, MAC and
other operating systems by such vendors as ChiliSoft, I would expect at a later
date to see the same evolve with ASP.NET.
Some newer development tools for ASP.NET can be downloaded at http://www.asp.net, a branch off of the
Microsoft Development website, or from http://www.asp101.com.
Just as ASP utilized a .asp extension for the server
to process it as a ASP page, pages designed with ASP.NET use a .aspx extension
for the server to process them. Where
before there were a few languages being used to process ASP pages, now new
languages have been created to run ASP.NET, most common are C# - a simpler
version of C++, Visual Basic.NET – another and similar version of Visual Basic,
and Jscript.NET – A JavaScript based language specifically designed for
ASP.NET. The ASP.NET pages can be
written with a text editor such as notepad in the same way that ASP pages could
be, but there are developer tools that are currently free such as the ones
found at the webmatrix project found at http://www.asp.net
that are windows based and offer many shortcuts in developing the pages by
point and click. The developing tools
are not unlike the Visual Basic InterDev tools from before and can be pretty
complicated for beginners but if you have some programming background ASP.NET
will be easier and offers a lot of time-savers in its development.
ASP.NET promises to provide unprecedented developer
productivity with performance, reliability, and easier deployment.
Developer
Productivity
– This obtained by an easier programming model that uses far less amounts of
code than was previously required with classic ASP. This is done by using tools, and code that
are already built-in. It allows
displaying data, user input validation, and uploading files to be much easier
than ever before. ASP.NET now has more
flexibility with its programming language options. Application features that used to be very
difficult to implement, or required purchasing third party components can now
be added by just a few lines of code using the >NET Framework. These features are completely built in and
offers over 4500 classes that use features such as XML, data access, file
uploading, commonly used expressions, image generation, performance monitoring
and logging, SMTP mail, and so on.
Improved
Performance and Scalability – ASP.NET is much faster than classic ASP offering less
tasking of the server to perform its functions.
It does so by using compiled execution it which the ASP.NET will
automatically detect any changes to the page and dynamically compile the files
as necessary rather than having to send information from a web page to be
processed and then sent to another page for display. Output caching allows a page to be executed
just once and then it saves the information from the page in memory in addition
to sending it to the user. When another
user requests the same page ASP.NET will serve the cached result from memory on
the hard drive rather than have to process the script multiple times. Output caching is also configurable and can
cache just part of a result or the entire result. A comparable test was ran using Sun’s Java
Pet Store J2EE blueprint application against the same setup using ASP.NET
implementation. The ASP.NET
implementation required 1/4th as many lines of code, was 28x faster,
and supported 7.6x as many concurrent users as J2EE, with only 1/6th
the amount of processor utilization.
Enhanced
Reliability
– ASP.NET will automatically detect and recover from errors such as deadlocks
and memory leaks. If a web application
ties up a significant percentage of the server’s virtual memory due to a memory
leak, ASP.NET will automatically create a copy of the ASP.NET worker process
and direct all the new requests to the newly created process. Once the old process has finished all pending
requests, it is automatically disposed and the leaked memory is released
freeing up the server’s resources. No
administrator intervention is required and no interruption of service will
occur.
Easy
Deployment
– When a web application is created using ASP.NET similar CLASS objects or COM object used for specific
functionality on classic ASPs, it is not necessary to input them into the
registry or adjust configuration settings in an XML file. It merely needs to be present in the web
servers root directory. When objects are
updated now, they can be copied over the existing DLL files and the server does
not need rebooted, ASP.NET will detect the change and start using the newer
copy. Migration from classic ASP to
ASP.NET is very simple. Since both of
them use separate scripting engines, they can both be ran on the same server
and pages can be migrated one at a time until they are completed.
New
Application Models – With ASP.NET developers can take advantage of XML web services that
allow applications to communicate over the Internet, regardless of the
Operating Systems. It is also very easy
to call on XML service with just a line of code, it isn’t necessary to have to
have knowledge of XML, networking, or SOAP.
ASP.NET also has built in Mobile Controls that easily target cell
phones, PDAs, and other mobile devices.
After writing an application there are converters that will
automatically generate WAP/WML, HTML, or iMode as required by the requesting devices.
Conclusion
ASP and ASP.NET offer a great deal of benefits to web
developers wanting to build tailor-made, and powerful web sites. Many banks, e-commerce sites, database
oriented websites, and colleges use ASP due to it’s flexibility, ease of programming
and common security from the user.
However, throughout my research there were cons to the pro. Because of the widespread use of IIS which is
required for ASPs to run on, it makes it a larger, not easier, target for
hackers. Microsoft continually submits
updates for IIS in order to try to counter and stay ahead of the hackers’
ploys.
ASP.NET will certainly prove to be the next generation
of web development available. Microsoft
has continually migrated towards XML platforms and making their operating
systems more web friendly. ASP.NET has
offered another step in the coercion of platforms which will separate its web
server platforms from other choices, for now.
Either way, it has provided a huge step for it’s competition to meet,
and will drive competitors to be more innovative in their designs, thus only
providing a huge benefit in web technology for the consumers.
References
Cox,
Keith (1997, December) Active Server Pages (An introduction to web-based
application development) <http://www.abiglime.com/webmaster/articles/asp/122297.htm>
Gunesh,
Arun (2002) Active Server Pages <http://www.developer.be/index.cfm/fuseaction/tutorialDetail/GroupID/50/tutorialName/IntroductiontoASPNET.htm>
Burns,
Joe, Phd. (2002) So you want ASP huh? <http://www.htmlgoodies.com/beyond/asp.html
>
ZDNet
(
Hitmill.com
(
Microsoft
Corporation (2002) Why ASP.NET <http://www.asp.net/whitepaper/whyaspnet.aspx
>
Peterson,
John (2002) Microsoft ASP.NET Web Matrix Project – Version 0.5 <http://www.asp101.com/articles/john/aspnetmatrixb1/default.asp>