The World Wide Web has quickly become an important pedagogical tool for a large number of Earth science instructors. These instructors use Web sites to supplement on-campus courses or deliver educational material at a distance. In most cases, the Web sites used in these situations are static in nature. That is, each Web page exists as a separate and complete file on a Web server. Unfortunately as the scale and complexity of a Web site grows, a static web site is subject to many shortcomings and limitations. These focus on around maintaining and upgrading large sites, providing personalized information and imposing security. As a Web site grows in quantity and content scope, site maintenance becomes an increasingly time-consuming task. Simple changes in content or navigational scheme may require altering hundreds of pages individually. At the same time, the addition of content requires, at the least, a rudimentary knowledge of HTML. Static Web sites also deliver the same content to every visitor; therefore, they are unable to customize the requested Web page to the needs of an individual visitor. Similarly, devising methods to permit selected users access to different parts of the Web site is difficult.

Database-driven dynamic Web sites offer a means of overcoming many of the shortcomings and limitations of static Web sites. Dynamic sites contain Web pages whose content is not fixed. Unlike static sites, dynamic Web pages do not exist as separate and complete individual files on the server. Instead, Web pages consist of HTML templates with additional scripting tags inserted. When such a page is requested by a Web browser, information is automatically extracted from the database and inserted into the template before it is sent to the browser. Thus, Web pages can be customized based upon the identity of the visitor, the content requested, the time of the request, the date of the request or the Internet location of the requesting client. Indeed, there is a limitless number of ways in which content can be tailored to meet identified needs.

Dynamic Web sites function in one of two different modes. In the read-only format, content is retrieved from a database and displayed to the user in a typical Web page. The user can read the Web page, but can not change its content. A read-only format is common for the public portions of a Web site. Conversely, a user may be able to enter new data into the database or update existing information thereby changing the Web content. In this situation, the user is presented with a series of Web forms through which he/she interacts with the database. Typically, this ability is provided to only a subset of a site¼s visitors. The extent to which the content or structure of a Web site is generated from a database can vary greatly. At one end of the spectrum, the site may contain only a few dynamic pages, i.e. pages built from the database. Conversely, all the pages of a site as well as its structure can be generated from a database.

In the Earth sciences, dynamic web sites have many potential applications, for both an individual instructor and an entire department. Utilizing dynamic Web sites, we have created a Class Management System (CMS) for several geology classes at the University of Wyoming. CMS determines what functions are available to the Web site visitor depending upon their status, e.g. student, teaching assistant or faculty member, and maintains database security. Although our application supports a variety of courses simultaneously, student access is limited to those portions applicable to the course he/she is taking. Homework assignments, extra credit problems, reading questionnaires and lab exercises are delivered, submitted and graded via the Web and CMS. For each student, a Web-based class grade book catalogs completed work, the grades for this work and activities not yet handed in. Grades are summed and tracked by the Web site. Via the Web, students view their individual "pages" in the grade book and compare how they are doing with respect to the entire class. Complementary Web applications maintained by a database and customized to individual courses allow students access to a practice test bank, glossary and image bank. Web pages available to teaching assistants through CMS permit them to grade Web-submitted exercises, extend activity due dates for individual students, enter grades for activities not completed on the Web and communicate electronically with individual students or the course instructor. An instructor can create and modify exercises, set and extend due dates for the entire class or individual students, enter exam grades and add or modify the Web site¼s content. At the department level, dynamic Web sites permit an Earth science department to maintain easily up-to-date Web sites, customize content to different external and internal audiences and use a number of individuals to maintain the site content. In light of these benefits, the Department of Geology and Geophysics at the University of Wyoming is currently replacing its static Web site with a dynamic version. When completed, the new Web site will be easier to maintain, offer a greater range of services and spread responsibility for Web site maintenance across a broader spectrum of the department. Because the content of the Web site will be hosted in the database, different individuals will be assigned different parts of the Web site to maintain. Using Web forms, they will be able to update and revise the content of their areas without the assistance of a "Webmaster". For example, the individual in charge of the speaker¼s series will update the speaker¼s list through a Web form. This individual will not need to know HTML and cannot inadvertently modify the HTML code of the speaker¼s page. By controlling access to the Web site with a database, Web authors will not be able to inadvertently overwrite someone else¼s changes. Using a similar approach, faculty, research scientists and graduate students will make changes directly to their departmental pages and not need to contact a åWebmaster¼.

Dynamic Web sites are created using three different but complementary computer technologies. These are: a Web server, a Web application server and a database. When the visitor accesses a Web page, the Web server determines if the file on the server is a complete HTML page or if it contains special code requesting information from a database. A complete HTML page is simply sent to the requesting browser without additional processing. If special codes are detected in the requested file, the Web server calls the Web application server. This program requests the required information from the database. It formats this information into accepted HTML syntax and passes the resultant text string back to the Web server. The Web server combines this information with the HTML in the template and sends the completed Web page to the browser for display on the client computer. Because processing occurs on the Web server/database server(s), the browser or computer platform used by the visitor is immaterial. Using this type of configuration, a Web site can be maintained by individuals who lack HTML skills through a series of Web-based forms. By filling in these forms and submitting them, the content of the Web site can be updated, changed or modified. At the same time, the security provided by the database and/or the Web server ensures that only those individuals with appropriate access can change the Web site.

Although there are many hardware and software solutions that can produce such sites, one of the easiest to create utilitizes a variety of Microsoft technologies and software. In this arrangement, the Web server is Internet Information Server (IIS). It comes standard with Microsoft Windows NT Server and can run on a variety of hardware configurations. Also included with Windows NT Server is the Active Server Pages scripting engine. This scripting environment communicates between IIS and a database. In this type of arrangement, there are two possibilities for the back-end database. One is Microsoft Access. This database comes with Microsoft Office Professional and is very easy to use. It uses a graphical interface to step the novice through the steps necessary to create a database. Although extremely helpful, one need not know SQL, the language of relational databases, to use Access. The major drawback with Access is that it can handle only a small user load. Web sites for classes with large enrollments that will generate many simultaneous hits on the Web site will encounter performance problems using Access. Microsoft¼s SQL Server is capable of handling multiple users but is expensive and requires a thorough knowledge of SQL to design, create, build and maintain the database. Dynamic Web sites offer numerous advantages over static Web sites, but they also have several serious drawbacks. They require a more complicated hardware and software solution than static Web sites. Their creation involves three very different technologies, e.g. HTML and Web servers, Web application servers (e.g. CGI or ASP) and database design, creation and maintenance. For this reason, a team that brings many different technical capabilities is generally necessary to develop dynamic Web sites. Although maintenance and upgrading of a dynamic Web site can be simpler and carried out by individuals with little Web experience, implementation of these capabilities requires considerable up front planning and development time. This initial investment is subsequently recovered by simplified Web site maintenance; however, few departments can currently justify such long-term returns. Using a database to store Web content, course exercises and student work requires regular and systematic back-up of the database. A hardware or software failure that leaves the database inaccessible or not recoverable will have dire consequences for both students and faculty. The Web server-database communication uses custom scripts and programs that interface the two software applications. When a department or class Web site is hosted on a university server, the information technology unit responsible for operating the server may be reluctant to allow individual departments or instructors the ability to place such custom applications on the server.

Despite their additional requirements, dynamic Web sites have many advantages for the delivery of Earth science educational material. They allow a Web development team to design Web sites that accommodate a variety of users, impose different security levels on various parts of a Web site, simplify changes to site content or structure, provide a means of maintaining the site by individuals with little or no HTML experience, and provide for future scalability and content scope expansion. Given these benefits, it is little wonder that dynamic Web sites have become the norm for large commercial Web sites. By committing the resources and time necessary to develop dynamic Web sites, Earth science departments can significantly improve the quality and breadth of their educational Web sites, achieve a wider variety of pedagogical goals and attract a larger Web audience.