The World Wide Web has dramatically changed the online world and continues to grow in popularity. As a communication system, the Web can give information providers the ability to distribute and collect information globally and instantly. For users, the Web is a dynamic view into the works and ideas of millions of people and organizations worldwide. With origins in ideas about nonlinear thinking, the Web is an information integrator on the Internet and plays a major role in online cyberspace.
What Java brings to the Web is a new way of communicating. Instead of relying on the Web servers to provide information and functionality, Java’s executable content makes Java-enabled Web browsers “smart.”
This chapter briefly explores how Java transforms the World Wide Web. The Web supports a range of communication, information, and interaction using hypertext for organizing information. Multimedia used with hypertext, called hypermedia, can enrich the Web’s information. Special programming techniques used with the Web’s hypertext, such as gateway programming or languages such as Java or Virtual Reality Modeling Language, can expand the Web’s possibilities for interactivity, information delivery, and communication.
To learn Java’s power as it can be used for the global distribution of information, you should first understand what the Web is and the significance of Java’s changes to it. If you are a seasoned Web user, you probably have already realized from the previous two chapters how Java extends the Web’s potential; you might want to skip to Chapter 4 to begin looking at specifics. This chapter takes a close look at the Web and Java’s part in it.
The World Wide Web was originally developed to meet the information needs of researchers in the high-energy physics community. Today, the World Wide Web offers a system for distributing hypermedia information locally or globally. Technically, the World Wide Web enables a seamless, global system of multimedia communication. This information is organized associatively and delivered according to user requests. This section briefly surveys the historical origins of the Web and how the confluence of ideas in network technology has reached fruition in the global Web of today. Java is just the latest installment of a series of innovations in hypertext and Web communication.
Vannevar Bush described a system for associatively linking information in his July 1945 article in The Atlantic Monthly, “As We May Think.” (This article is available on the Web at http://www.isg.sfu.ca/~duchier/misc/vbush/.)
Bush called his system a memex (memory extension), and proposed it as a tool to help the human mind cope with information. Having observed that previous inventions had expanded human abilities for dealing with the physical world, Bush wanted his memex to expand human knowledge in a way that took advantage of the associative nature of human thought.
In 1965, Ted Nelson coined the term hypertext to describe text that closely followed Bush’s model, in that Nelson’s text was not constrained to be sequential. Hypertext, as Nelson described, links documents to form a web of relationships that draw on the possibilities for extending and augmenting the meaning of a “flat” piece of text with links to other texts. Hypertext is more than just footnotes that serve as commentary or further information about a text; rather, hypertext extends the structure of ideas by making “chunks of” ideas or information available for inclusion in many parts of multiple texts. Nelson also coined the term hypermedia, which is hypertext not constrained to be text. Hypermedia can include expressions of multimedia—pictures, graphics, sound, and movies.
Vannevar Bush’s and Ted Nelson’s ideas about information systems showed up in another project in the late 1980s. In March 1989, Tim Berners-Lee, a researcher at the Conseil European pour la Recherche Nucleaire (CERN) European Laboratory for Particle Physics in Geneva, Switzerland, proposed a hypertext system to enable efficient information-sharing for members of the high-energy physics community. Berners-Lee had a background in text processing, real-time software, and communications, and had previously developed a hypertext system he called “Enquire” in 1980. Berners-Lee’s 1989 proposal, called “HyperText and CERN,” circulated for comment. The following were important components of the proposal:
By late 1990, an operating prototype of the World Wide Web ran on a NeXT computer, and a line-mode user interface (called “WWW”) was completed. The essential pieces of the Web were in place, although not widely available for network use.
Throughout the early 1990s, interest in the Web grew and spread worldwide. In March 1991, the WWW interface was used on a local network, and by May of that year, it was made available on central CERN machines. On January 15, 1992, the WWW interface became publicly available from CERN, and the CERN team demonstrated the Web to researchers internationally throughout the rest of the year.
In 1993, interest in the Web grew very rapidly. A young undergraduate who was then at the University of Illinois at Urbana-Champaign named Marc Andreessen worked on a project for the National Center for Supercomputing Applications (NCSA), and lead a team that developed a browser for the Web called Mosaic. The group released an alpha version of Mosaic for the X Window System in February 1993 that was among the first crop of graphical interfaces to the Web. Mosaic, with its fresh look and graphical interface presenting the Web using a point-and-click design, fueled great interest in the Web and online information. By the end of 1993, attendees at the Internet World conference and exposition in New York City were eager to learn about graphical interfaces to the Web. The New York Times hailed Mosaic as the Internet’s “killer application.”
In 1994, more commercial players got into the Web game. Companies announced commercial versions of Web browser software, including Spry, Inc. Marc Andreessen and colleagues left NCSA in March to form, with Jim Clark (former chairman of Silicon Graphics), a company that later became known as Netscape Communications Corporation ( http://home.netscape.com/). By May 1994, interest in the Web was so intense that the first international conference on the World Wide Web, held in Geneva, overflowed with attendees. By June 1994, there were 1,500 known public Web servers.
By mid-1994, it was clear to the original developers of the Web at CERN that the stable development of the Web should fall under the guidance of an international organization. In July, the Massachusetts Institute of Technology (MIT) and CERN announced the formation of the World Wide Web Consortium, or W3C.
Today, the W3C ( http://www.w3.org/hypertext/WWW/Consortium/) guides the technicaldevelopment and standards for the evolution of the Web. The W3C is a consortium of universities and private industries, run by the Laboratory for Computer Science (LCS) at MIT collaborating with CERN ( http://www.cern.ch/), and Institut National de Recherche en Informatique et en Automatique (INRIA), a French research institute in computer science (http://www.inria.fr/).
In 1995, the development of the Web was marked by rapid commercialization and technical change. Netscape Communication’s Mozilla browser continued to include more extensions of the HyperText Markup Language (HTML), and issues of security for commercial cash transactions garnered much attention. By May 1995, there were more than 15,000 known public Web servers, a tenfold increase over the number from a year before. Many companies had joined the W3C by 1995, including among others, AT&T, Digital Equipment Corporation, Enterprise Integration Technologies, FTP Software, Hummingbird Communication, IBM, MCI, NCSA, Netscape Communications, Novell, Open Market, O’Reilly & Associates, Spyglass, and Sun Microsystems.
By mid-1995, the emergence of the Java and Virtual Reality Modeling Language (VRML) technologies placed the Web at the start of another cycle of rapid change and alteration. Java, in development for several years at Sun Microsystems, promises to make the Web far more interactive than ever before possible. (See Chapter 1, “Java Makes Executable Content Possible.”) Virtual Reality Modeling Language, which can allow developers to model three-dimensional scenes for delivery through special Web browsers, may also dramatically change what the Web has to offer. For more information on VRML, see Chapter 34, “VRML and Java.”
Despite its rapid growth and technical developments, the Web in 1996 retains the essential functional components it had in its 1990 form. Its popularity as a view of the Internet, however, has muddied popular understanding of it, because the Web is sometimes viewed as equivalent to the Internet and browsers are sometimes thought of as equivalent to the Web rather than a view into it. However, the Web is a very distinct system from the Internet and its browsers. First, the Web is not a network, but an application system (a set of software programs). Second, the World Wide Web can be deployed and used on many different kinds of networks (not necessarily just Internet networks) and it can even be used on no network at all or on a local network unconnected to any other.
| A METAPHOR FOR THE WEB |
|---|
| Imagine a library in which all the spines of the books have been removed and the gravity in the building has been turned off, allowing the pages to float freely. If people could connect one page to another using very light threads taped to the pages, this would be similar to the way the Web’s hypertext is arranged. Pages free-float, so that users might encounter a work from any page within it, and reach other works by following the threads leading off a page. |
Here is a more technical definition of the Web:
The World Wide Web is a hypertext information and communication system popularly used on the Internet computer network with data communications operating according to a client/server model. Web clients (browsers) can access multiprotocol and hypermedia information.
Figure 3.1 summarizes the technical organization of the Web based on this definition.
FIGURE 3.1.
The technical organization of the Web.
Java changes the Web by bringing more “intelligence” to Web browsers. Although Java-enabled browsers have user interfaces that are much the same as many other Web browsers, their technical operation marks a significant shift in focus. Java’s executable content requires Java-enabled browsers to be smart; that is, they must be able to interpret executable content.
A client-server model for networked computer systems involves three components: the client, the server, and the network. A client is a software application that most often runs on the end-user’s computer host. A server is a software application that most often runs on the information provider’s computer host. Client software can be customized to the user’s hardware system and it acts as an interface from that system to information provided on the server. The user can initiate a request for information or action through the client software. This request travels over the network to the server. The server interprets the request and takes some desired action. This action might include a database lookup or a change in recorded database information. The results of the requested transaction (if any) are sent back to the client for display to the user. All client/server communication follows a set of rules, or protocols, which are defined for the client/server system. Figure 3.2 summarizes these relationships, showing the flow of a request from a client to a server and the passing back of information from a server to a client. A client might access many servers employing the protocols both the server and client understand.
The distributed form of “request” and “serve” activities of the client/server model allows for many efficiencies. Because the client software interacts with the server according to a predefined protocol, the client software can be customized for the user’s particular computer host. (The server doesn’t have to worry about the hardware particularities of the client software.) Forexample, a Web client (a browser) can be developed for Macintosh computers that can access any Web server. This same Web server might be accessed by a Web browser written for a UNIX workstation running the X Window system. This makes it easier to develop information, because there is a clear demarcation of duties between the client and the server. Separate versions of the information need not be developed for any particular hardware platform, because the customizations necessary are written into client software for each platform. An analogy to the client/server model is the television broadcast system. A customer can buy any kind of television set (client) to view broadcasts from any over-the-air broadcast tower (server). Whether the user has a wristband TV or a projection screen TV, the set receives information from the broadcast station in a standard format and displays it appropriate to the user’s TV set. Separate TV programming need not be created for each kind of set, such as for color or black-and-white sets or different size sets. New television stations that are created will be able to send signals to all the currently in-use television sets.
FIGURE 3.2.
A client/server model for data communication.
Java brings another dimension to the client/server model. Of course, Java does follow the basic model: A Java-enabled browser is a client that sends requests to Web servers for information. The Java-enabled browser interprets and displays the information sent from the server. This information includes both the hypertext as well as any bytecodes. These bytecodes are Java’s new twist on this model. The Java clients execute the content distributed from the servers. These bytecodes, as described in Chapter 2, are also architecture-neutral, just like the other information sent from the Web server.
Helper applications include software that a (non-Java-enabled) Web browser invokes to display multimedia information to the user. For example, in order for the user to view movies, the Web browser must have movie display software installed and available. To display inline graphical images in an HTML document, the Web browser must be graphical—that is, employ a system such as X Window system, Macintosh Operating System, or Microsoft Windows as a graphical user interface.
Instead of relying on helper applications, programmers developing applets for Java-enabled browsers can create content handlers to handle media formats.
The Java language and its browsers are part of the larger context for communication on the Web. Whether you write and distribute applets or just observe them, you take part in communication activities and traditions that have been developing on the Web for many years. Because Java is still so new, it has not yet appeared in all Web communication contexts. You’ll see more specific examples of Java used on the Web in later chapters of this book. This subsection briefly reviews the Web’s context and potential and how Java can be a part of it.
Communication on the Web can take many forms and take place in many contexts. Genres, or traditional ways for communicating, have evolved on the Web. These genres correspond, in many ways, to offline human communication contexts:
The key concept to understand is that the Web as a communication system can be flexibly used to communicate in a variety of ways. The classification of the communication (in the categories listed) depends on who is taking part in the communication. The exact classification of any expression on the Web can be blurred by the potentially global reach of any Web page. Thus, a personal home page may be used interpersonally, but it may be accessed far more times on the Web than a publication created and intended for mass consumption. Java’s capability for delivering interactive content adds new possibilities to each of these categories.
The Web is a flexible system for communication that can be used in many contexts, ranging from individual communication on home pages through group communication and mass communication. In addition to these contexts, the Web also serves the following functions:
Figure 3.3 shows the important distinction between selectivity and gateway programming interactivity. When the user accesses the Web server on the left, content is presented using hypertext. The links in the hypertext pages give the user a great deal of choice, or selectivity, for encountering information in the database. However, no information is customized to user inputs or computed based on user requests. Although this server offers the user great flexibility in information retrieval because of the hypertext design of its pages, this server is not interactive.
The key to the level of interactivity, as shown in the server on the right, is that the executable program accepts input from the user through a Web page. Based on these user inputs, this executable can compute a result and (possibly, also using information from the database) return this customized information result to the user. Moreover, the executable program also enables the user to (possibly) change the contents of the database, or make some other change in the database or files on the server. These changes might include altering the structure or contents of hypertext or the contents of other files. The construction of this executable program requires skills in gateway programming.
Java adds still another level of interactivity. Instead of the server computing a result, the Java-enabled browser is the mechanism for computation.
FIGURE 3.3.
Web selectivity and gateway interactivity.