Special Edition Using SGML:Understanding the Information Revolution: The New Paradigm

Modular Document Sharing Is Only the Beginning

You have learned how to make documents available to anyone with a computer and a modem, including sound files, movies, and pictures. Most Web browsers can handle all these types of files. The excitement about sharing documents has led to new developments. Object-oriented programming applications can also interact with Web pages.

• See “How HTML and SGML Relate” p. 295

Java. The object-oriented programming language talked about the most today is Java. Java is an interpreted language that is multi-threaded and platform independent, developed from a team lead by Sun Microsystems. Check it out at http://java.sun.com or a mirrored site. You need a java-compatible browser, such as Netscape 2.0 or HotJava, that will support the special DTD fragment that enables HTML pages to contain Java programs. The programs themselves, like graphics in Web pages, are ignored by the HTML parser but are recognized by the Java-compatible browser and are executed. These browsers support a non-standard HTML extension expressed by the following DTD fragment:

      <!ELEMENT APPLET - - (PARAM*, (%text;)*)>
      <!ATTLIST APPLET
              CODEBASE CDATA #IMPLIED  -- code base --
              CODE CDATA #REQUIRED     -- code file --
              NAME CDATA #IMPLIED      -- applet name --
              WIDTH NUMBER #REQUIRED
              HEIGHT NUMBER #REQUIRED
              ALIGN (left|right|top|texttop|middle|
                      absmiddle|baseline|bottom|absbottom) baseline
              VSPACE NUMBER #IMPLIED
              HSPACE NUMBER #IMPLIED
      >
      <!ELEMENT PARAM - O EMPTY>
      <!ATTLIST PARAM
              NAME NAME #REQUIRED     -- The name of the parameter --
              VALUE CDATA #IMPLIED    -- The value of the parameter --
      >

The fact that HTML revisions come as slowly as they do is a disappointment for some because extensions like this <APPLET> tag seem to take forever to become implemented in the standard. This long lead time is perhaps another strong reason why the Web should adopt the full SGML standard, and so as not to encourage developers to violate the standard with extensions like these. Under full SGML, multiple DTDs and DTD fragments can be supported well within the accepted international standard.

The Web will change even more dramatically as more browsers support the <APPLET> element and Java. The implications for launching shared interactive applications over the Web are enormous. For example:

• People can watch a movie in real time, even if they’re physically separated by many miles.

• People can carry on a video conference with sound and video support from a Web browser.

• People can access the same spreadsheet in real time without overwriting the work of others.

• People can play interactive virtual reality games over the Web and launch programs that interact with one another. This is somewhat possible today over TCP/IP with the Kali IPX emulator (see fig. 30.1), as well as other possibilities over the Internet Relay Chat channels.

• Programmers can work on the same project in real time over a network and add value as the application develops.

You can learn many things from programming applications that run from Web browsers. Figure 30.2 shows a Java page that executes a little multimedia program where the developer’s smiling face bounces and revolves around in a little box. Other applications are more serious, of course, and the potential is enormous.

Fig. 30.2 Java is the first object-oriented program language designed to use the APP element.

Virtual Reality Modeling Language. Virtual Reality Modeling Language (VRML) incorporates even more graphic capability into Web pages through access to three-dimensional graphic files that can constantly reorient themselves to give you the illusion that you are moving through a virtual world. Links to these *.wrl pages can be launched from an HTML page, but to interactively view the file, you need a VRML browser.

• See “Adding Multimedia Content,” p. 161

VRML actually goes outside the boundaries of SGML. It depends on SGML inasmuch as the World Wide Web depends on SGML, to provide an overall connected resource in which to store three-dimensional files.

When SGML was devised, it was primarily concerned with two-dimensional graphics. It can handle three-dimensional graphics, but they must be delegated to another application to be viewed. In other words, SGML turns the tasks over to another application and concentrates on what it does best, which is structural document handling. VRML is one of the many additional types of resources that SGML can accommodate in its open design philosophy. SGML was designed to allow many different types of resources to interact without obstruction from the requirements of the international standard. The fact that VRML has become so popular on the Web demonstrates that it can work right alongside SGML documents without interfering with them.

The possibilities for VRML are magnificent. With VRML browsers, you can chase your friends through three-dimensional, interactive worlds. Recall figure 1.10, which shows a scene from the virtual reality game Descent. That could be you. Likewise, imagine walking down a virtual street in Hong Kong and opening a door that leads onto a street in Copenhagen. In a virtual world, you can do that.

Many developers are creating VRML browsers. Figure 30.3 shows one that works on PCs called WebSpace.

Fig. 30.3 VRML resources like this have mushroomed on the Web.

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