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A beginner’s Guide into Microsoft’s Premiere Web
Technology |
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HTML |
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Lacking Dynamic Content |
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Used to transmit information between computers,
networks, and operating systems. |
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CGI (Common Gateway Interface) |
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First web interface. |
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Could be implemented in any number of
programming languages. |
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First applications were actually programs
written in C and C++. |
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Very cumbersome and time consuming. |
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Perl (Practical Extraction and Reporting
Language) |
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Simplified version of C and C++, however still
difficult to learn. |
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For a script to work with a Web Server there
needs to be some kind of intermediate application, or add-in, to connect
the two. It has to accept a request from the user, read and interpret the
appropriate server-based script file, and then create the output page and
communicate it to the Web server where it is sent as the response to the
client. |
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Typically the task is divided into two sections. |
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One application or add-in handles the
communication to and from the Web server. (CGI) |
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Another handles interpreting and executing the
script. |
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Perl was the first such popular server-side
scripting language. |
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Internet Information Server (IIS) 1.0 |
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Fairly standard offering. |
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Introduced an interface which allowed
executables written in C and C++ to operate more efficiently. |
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ISAPI (Internet Server Application Programming
Interface) |
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Provides the basis by which ASP connects to IIS,
as well as the other Microsoft server-side dynamic techniques. |
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The two major concerns when creating
applications that interface the Web server are their effect on the
stability of the Web server itself, and the efficiency with which they can
handle multiple and concurrent page requests. |
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In-Process |
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ASP |
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Pros |
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Fast. |
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Can directly access input and output in the Web
server’s memory address. |
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Cons |
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A failure or error in the code can bring down
the Web server. |
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Out-of-Process |
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Perl and .exe files that use the ISAPI
interface. |
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Pros |
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Failure of an out-of-process application will
not affect the Web server. |
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Can be terminated by the user or operating
system. |
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Cons |
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Slow. |
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Because access to the Web server’s memory is
forbidden – any input or output must be passed to the server via a
cross-process. |
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Latency caused by the loading and unloading of
the executable. |
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In-Process |
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ASP |
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Pros |
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Fast. |
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Can directly access input and output in the Web
server’s memory address. |
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Cons |
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A failure or error in the code can bring down
the Web server. |
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When ASP receives a page from IIS that contains
server-side script code, it parses it line-by-line. Anything that is not
server-side script, is sent back to IIS, and onwards to the client. As each
section of script is reached, it is passed to the appropriate scripting
engine. The results of which are inserted at the appropriate points as it
is sent to IIS. |
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Script is identified by either the <% %>
script delimiters or by using the <SCRIPT> element. |
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Pages have an extension of .asp |
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The default scripting language is VBScript,
however Jscript is a suitable alternative. |
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VBScript is NOT Visual Basic but is, in fact, a
subset of the actual language. |
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Jscript IS based on Netscape’s JavaScript with
the added feature of being able to be run at the server. |
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<%Language=“VBScript”%> |
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<html> |
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<body> |
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<% |
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Response.Write(“Hello World”) |
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%> |
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</body> |
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</html> |
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Request |
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Response |
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Application |
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Session |
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Server |
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ASPError |
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Makes available to our script all the
information that the client provides when requesting a page or submitting a
form. This includes the HTTP variables that identify the browser and the
user, the cookies that they have stored on their browser for this domain,
and any values appended to the URL, either as a query string or in HTML
controls in a <FORM> section of the page. |
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Is used to access the response that we are
creating to send back to the client. It makes available to our script the
HTTP variables that identify our server and its capabilities, information
about the content we’re sending to the browser, and any new cookies that
will be stored on their browser for this domain. It also provides the means
by which we produce output – such as the Response.Write which we saw
earlier. |
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Provides a repository for storing variables and
object references that are available to all the pages, which any visitor
can open. |
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Is created for each visitor when they first
request and ASP page and remains until the default timeout period. Much
like the application object, it provides a repository for storing variables
and object references. Unlike the application object this repository
remains in effect for the life of the session. |
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Provides us with a series of methods and
properties that are useful in scripting with ASP. The most obvious of which
is the Server.CreatObject method, which allows us to properly instantiate
other COM objects on to the server within the context of the current page
or session. |
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Is a new object in ASP 3.0, and is available
through the GetLastError method of the Server object. It provides a range
of detailed information about the last error that occurred in ASP. |
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Notes