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While CD-ROM freezers its digital content in a polycarbonate snapshot at replication time, a connected CD-ROM--one which builds in an online or Web link--can evolve into a product that may little resemble the original title. The CD-ROM/online hybrid provides greater relevance to disc users for months after publication, and can provide a higher level of interaction, including transactions, database updates, integrated search and retrieval, and much more.

When it comes to connecting a CD-ROM to the Web, the simplest approach is to use a browser as the interface for the disc's HTML-formatted data, and to link the user to absolute URLs embedded on disc. Many CD-ROM/Web hybrid titles to a step further, and access Common Gateway Interface (CGI) programs on a Web server that can update database records, format reports in HTML for presentation in the user's browser, post messages to a threaded chat forum, count the number of visitors to the Web site, read the environment headers from the client's requests, and generally allows the Web to operate dynamically in real time.

The problem with a disc that makes a call to its Web server is that an active Web connection is required--a condition that is not always available or desirable. An emerging trend is to embed a proxy Web server on the disc itself, to be installed on the user's PC for rich CGI interactions without an online connection. A proxy Web server is like a middleman, functioning as an intermediary server which forwards requests from the client on to another server. In the context of a CD-ROM/online hybrid title, the local proxy server can appear to the client as the server until the actual Web server is needed, and a connection must be made. Embedded proxy servers will typically use the default local host IP address of 127.0.0.1 to handle such functions as local searches, using engines that were designed for the Web, or any dynamically-written HTML that might be created on-the-fly in response to a database query.

Emerging "portable" Web products--titles made with MarketScape's WebCD engine are probably the best known today--can now embed more than GIFs and JPEGs into the thinnest of thin servers: a CD-ROM. Whether installed on hard drive during a title's installation or operating as an ActiveX control or Java bean from the disc itself, live interaction between CD-ROM-based browser and proxy server and a Web server is now a general publishing option that is becoming realistic and relevant, as more potential users are becoming Internet-connected. And the ability of these disc-based component servers to create autonomous portable custom client/server environments may be an essential ingredient in the mass popularization of the Internet among the general public, especially if the convergence between TV and the Web is to become widespread.

CGI: AN INTERACTION INTRODUCTION

So what types of disc-based interaction might be possible using Common Gateway Interface Web communication? Though client-side-only processing is possible and rich, interaction with a Web-based server is still the final goal for most connected-CD transactions.

The HTTP 1.0 protocol supports three methods of CGI communication: GET, HEAD, and POST. GET is used to request information from the server in an encoded Uniform Resource Identifier (URI), which combines the server's URL with escape characters, directory paths, and parameters. This is the method most often used in search engine requests, where the search parameters are placed in the URI itself when sent to the server. The HEAD method requests only a response header from the server, which is useful for checking the validity of links and obtaining environment information. The POST method sends data to the server in the form of a header, plus a body of information which is usually in text or HTML format. This is the common method used to submit HTML Form input that often appears as a textbox on a Web page to allow data input to a database.

In the following HTML excerpts, the Cisco Connection CD-ROM accesses first the local search engine, and then the Web-based one--both using the HTTP GET method.

Perl, C, and UNIX shell scripts are traditionally used on the server to interpret the sent data and output either a data table for updating a database or HTML text for return to the client. Although still new, increasingly Visual Basic and Java are being used in server-side CGI processing. And things are due to change even more: the new proposed HTTP 1.1 protocol has also added the Trace, Put, Delete, and Upgrade methods to these three original requests.

Some early examples of CGI-ROM occur on searchable CD-ROM titles using a Web browser as the client. These include San Jose, California-based Cisco Systems, Inc.'s Cisco Connection CD-ROM, which employs Verity, Inc.'s topicSearch engine to search across either the CD-ROM or the Cisco Web site for the latest tech support and service relating to Cisco products. topicCD-Web Publisher installs a local host server, which runs on the user's machine to field these search queries. Encyclopedia Britannica's Britannica CD is another early CGI-ROM title that employs Verity's topicSearch engine to serve up encyclopedia pages on-the-fly from either the disc or the Web.

FROM WEB TO DISC: FINDING THE CD

While not limited to browsable HTML-formatted discs, CGI-ROM activity might be achieved with many of the same tools and programs that Web CGI actions use. Because there is such an explosion of development in the area of Web server/browser interaction, some of this technology is sure to assist CD-ROM title publishing. These developments run the gamut from getting a simple browsable HTML-formatted disc to allow online orders via a standard HTML input box, to sophisticated Distributed Component Object Model (DCOM) or Common Object Request Broker Architecture (CORBA) distributed applications.

One toolset for creating a server extension that can integrate a local CD-ROM with the server's file system is WWWebDisk/SE 2.0, from Netherlands-based WWWebDisk. WWWebDisk is an HTTP 1.1-compatible Web server extension that can be installed on UNIX or Windows NT Web servers to direct the client to the latest or preferred version of any file in either the local or Web-based file set. After logging on to the WWWebDisk server, an HTTP Cookie, or a text file that is sent from server to user's hard drive, is received by the browser, which stores the logical drive location of the CD-ROM drive, as well as any login information that might be needed. WWWebDisk's Content Mixing then allows any Web page to mix CD-ROM-based media with the latest Web-hosted HTML files. Any individual file content can be replaced by another file on either the local disc or the Web, based on the files' timestamps. CGI functionality with a WWWebDisk-extended server is typically standard real-time CGI between client and Web server, taking advantage of WWWebDisk's redirections. Because the 2.0 version of WWWebDisk is compiled C code, these applications are fast and powerful.

Another key technology for translating CGI programs to the Windows environment is the Windows CGI Interface (Win-CGI). Written by Robert B. Denny, creator of HTTPD, the original Windows Web server that has evolved into O'Reilly & Associates' WebSite Pro 2.0, Win-CGI is a platform-specific outline for enacting Web applications on Windows clients and servers. Bob Denny states that "the rationale behind Win-CGI was to provide an interface to allow Visual Basic and Dbase to be used as Web programming tools." While Win-CGI allows CGI programs to run natively on a Windows server, it also provides a framework for allowing a Windows client to run a Windows CGI program locally, without any server. For the small publisher, Win-CGI enables basic HTML Form input to text files that can be emailed, faxed, or printed out later; these files are usually written to the TEMP environment, unless otherwise directed by the Win-CGI program.

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