Web Technologies and Publishing On the Web Applications • Writing HTML with a text editor allows to generate web pages. These pages are said static Winter 2001 in the sense that they do not change. CMPUT 499: Dynamic Pages • What if we want to personalize pages for particular visitors or events? Dr. Osmar R. Zaïane • What if we want to have actions on the page? • What if the content of the page is from a database? University of Alberta • Etc. Dr. Osmar R. Zaïane, 2001 1 Dr. Osmar R. Zaïane, 2001 2 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta Course Content Objectives of Lecture 7 • Introduction • Databases & WWW Dynamic Pages Dynamic Pages • Internet and WWW • SGML / XML • Protocols • Managing servers • Introduce some technologies for dynamic • HTML and beyond • Search Engines insertion and modification of page content • Animation & WWW • Web Mining • Java Script • CORBA • Discuss the automatic generation of page • Dynamic Pages • Security Issues content • Perl • Selected Topics • See a concrete example of DHTML. • Java Applets • Projects Dr. Osmar R. Zaïane, 2001 Dr. Osmar R. Zaïane, 2001 3 3 4 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta
Outline of Lecture 7 Dynamic pages • What are Dynamic Pages? • Dynamic pages are pages that change • Server-Side Includes (SSI) • Dynamic pages are not static by definition • Conditional SSI (XSSI) • The change can be the fact that the page is never the same when downloaded again • Generating Pages on the fly • The change can be that the content of the • Dynamic HTML page is different for different visitors • DHTML Example (sliding menu) • The change can be generated by interaction Dr. Osmar R. Zaïane, 2001 5 Dr. Osmar R. Zaïane, 2001 6 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta Static versus Dynamic Problems with cache Request URL URL Request • Browsers cache web pages to avoid fetching them again. • If a page is meant to be different each time it is HTML page Response Response HTML page visited we should not cache it. Request URL • Force the browser to flush the cache by Dynamic Dynamic expiring the page or requesting that the on the on the browser does not cache the page client server • Some type of pages are by default not cached Response HTML page Dr. Osmar R. Zaïane, 2001 Dr. Osmar R. Zaïane, 2001 7 8 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta
Outline of Lecture 7 Server Side Includes • What are Dynamic Pages? • Server side Includes (SSI) are commands that are “included” in HTML documents • Server-Side Includes (SSI) and are executed on the “server side” • Conditional SSI (XSSI) • The server parses the HTML document • Generating Pages on the fly containing SSI and replaces the commands • Dynamic HTML by the result of their execution • DHTML Example (sliding menu) • A web server has to be configured to parse HTML documents and process SSI Dr. Osmar R. Zaïane, 2001 9 Dr. Osmar R. Zaïane, 2001 10 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta Enabling Server-Side Includes Syntax for SSI • Web server has to be instructed to parse • Server-Side Includes are embedded inside the HTML documents addType text/html .shtml addHandler sever-parsed .shtml HTML document as HTML comments • Parsing HTML documents adds an overhead <!-- server-side include --> • Only files that contain SSI need to be parsed • There are different recognized commands • Usually HTML files with SSI have .shtml as called SSI elements suffix <!--#element attribute=value attribute=value … --> • What if a HTML document with SSI is not • Values are usually enclosed between double parsed? quotes and there is often only one attribute Dr. Osmar R. Zaïane, 2001 Dr. Osmar R. Zaïane, 2001 11 12 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta
Other SSI Elements Allowed SSI Elements • exec executes a given shell command or • config controls aspects of parsing cgi. The valid attributes are: – Valid attributes are: • cgi the server executes the cgi which is • errmsg a message that is sent back to the client given the QUERY_STRING variable if an error occurs during parsing • cmd the server executes the given string • sizefmt sets the format to be used when using /bin/sh displaying the size of files ( bytes/abbrev ) • fsize prints the size of specified file • timefmt sets the format to print dates subject to sizefmt in config • echo prints an include variable or environment variables • file file relative to the current directory • virtual file relative to the current document – There are many available variables Dr. Osmar R. Zaïane, 2001 13 Dr. Osmar R. Zaïane, 2001 14 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta Other SSI Elements (con’t) Other SSI Elements (con’t) • flastmod prints the last modification date of • printenv prints all existing environment specified file. Same attributes as fsize variables • include inserts the text of a specified • set sets values of variables document. (no absolute path and no ../) – For example: • file file relative to the current directory • <!--#set var=“foo” value=“bar” --> • virtual file relative to the current document • <!--#set var=“who” value=“${ REMOTE_HOST }_${ REQUEST_METHOD }” --> Dr. Osmar R. Zaïane, 2001 Dr. Osmar R. Zaïane, 2001 15 16 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta
Include Variables Example for SSI • DATE_GMT • The current date in Greenwich Mean Time • DATE_LOCAL <!--#include file=“.. -->” <!--#include file=“..” -->” Home Products Services Contact-us • The current date in local time zone • DOCUMENT_NAME <!--#exec cmd=“..” -->” Welcome Mr. John Smith • The file name of the document requested • DOCUMENT_URI • The URL path of the document requested • LAST_MODIFICATION Today is Thursday February 8 th 2001 <!--#echo var=“..” -->” • The last modification date of the document requested Dr. Osmar R. Zaïane, 2001 17 Dr. Osmar R. Zaïane, 2001 18 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta Adding Code Logic to SSI Outline of Lecture 7 • Conditional SSI (XSSI) is a feature • What are Dynamic Pages? supported by Apache servers. IIS and Netscape servers may also support it. • Server-Side Includes (SSI) • Allows to execute different commands • Conditional SSI (XSSI) depending upon environment variables • Generating Pages on the fly • There are 4 flow-control statements • Dynamic HTML <!--#if expr=“expression” --> • DHTML Example (sliding menu) <!--#elif expr=“expression” --> <!--#else --> <!--#endif --> Dr. Osmar R. Zaïane, 2001 Dr. Osmar R. Zaïane, 2001 19 20 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta
Examples of XSSI Test Conditions • Loading a different file depending on browser • The test condition could be only one of the following: � String (true if String not empty) <!--#if expr= “${HTTP_USER_AGENT} = /Mozilla/” --> � String1 = String2 <!--#include file=“netscapebar.html” --> String could be a regular � String1 != String2 <!--#elif expr=“${HTTP_USER_AGENT} = /MSIE/” --> expression with unix egrep � String1 < String2 <!--#include file=“iebar.html” --> syntax /string/ � String1 > String2 <!--#else --> � String1 <= String2 <!--#include file=“defaultbar.html” --> Conjunction and � String1 >= String2 disjunction are && and || <!--#endif --> Dr. Osmar R. Zaïane, 2001 21 Dr. Osmar R. Zaïane, 2001 22 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta Dynamically Generated Pages Outline of Lecture 7 Request URL • What are Dynamic Pages? • Server-Side Includes (SSI) • Conditional SSI (XSSI) • Generating Pages on the fly Response HTML page • Dynamic HTML • DHTML Example (sliding menu) • Initially, the pages don’t exist on the server • Pages are created on the fly when requested Dr. Osmar R. Zaïane, 2001 Dr. Osmar R. Zaïane, 2001 23 24 Web Technologies and Applications University of Alberta Web Technologies and Applications University of Alberta
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