Control Choices and Network Effects in Hypertext Systems

E. James Whitehead, Jr.
Dept. of Information and Computer Science
University of California, Irvine


A key element of open hypermedia systems is the provision of hypermedia services to the multiple applications populating a typical user's computing environment.  A reaction against monolithic hypermedia systems which control the user interface, data, and hypermedia structure, open hypermedia systems control the hypermedia structure, and sometimes the data, but relinquish control over the user interface.  Gaining strength from less control, open hypermedia systems increase hypermedia network effects by including more applications, hence more content, in the hypermedia web.

The World Wide Web was designed to be a single point of entry into a distributed, multi-platform information space, and as a direct consequence chose different control tradeoffs.  With the Web, the user interface is controlled via the browser, but the data and hypermedia structure are uncontrolled.  Through these control choices, and the URL, HTML, and HTTP standards, the Web created a feedback cycle of positive network effects. This paper examines how the core differences in control assumptions between monolithic hypermedia systems, open hypermedia system, and the Web, lead to different levels of network effects.

1. Introduction

Hypertext systems exhibit network effects [Rohlfs, 1974], where the utility of the hypertext system depends on the number of users and amount of data in the system.  This differs markedly from traditional goods where the utility of the good does not depend on the number of other people who own the good.  Breakfast cereal has the same usefulness whether 1 or a million people own it.  In contrast, 1 telephone has no utility, and two have not much more.  But when a million, or a billion people have telephones, the utility of a single telephone is immense.

Network effects in hypertext systems have many causes. Hypertext system utility can be viewed from the perspective of readers, and of data, or content providers. From the perspective of a reader, a hypertext link between two documents increases the usefulness of both documents by making a relationship between the documents explicit, and reducing the burden of retrieving the associated information. As the number of links increases, the utility of documents in the system is greater than those outside the system. For the content provider, the utility of each document in the system is related to the number of people who read it. As more people use the system, it is likely more people will access the content generated by a provider.

Simple feedback loops lead to increases in readers and content providers.  Readers are lured to the system to take advantage of the greater utility of content in the hypertext system.  As more readers use the system, content providers have incentive to add more content.  Content entices readers, readers incentivize content, and so on. Past a critical threshold, this feedback cycle causes users to be locked-in to the hypertext system as competing systems are unable to generate sufficient network effects to supplant the dominant system. Such is the case with the World Wide Web today.

For monolithic hypertext systems, the goal was to create a system that provided hypertext functionality. Open hypermedia systems and the Web went further, wanting to provide hypermedia functionality in more open contexts than could be addressed by the monolithic systems. Due to these differing goals, each class of hypermedia system made different control decisions in its architecture. Monolithic hypertext systems control the user interface, hypermedia structure, and data, while open hypermedia systems control the hypermedia structure, and sometimes the data, but relinquish control over the user interface. With the Web, the user interface is controlled via the browser, but the data and hypermedia structure are uncontrolled.  This paper examines how these core differences in control assumptions between monolithic hypertext systems, open hypermedia systems, and the Web, lead to different incentive structures for readers and content providers and hence varying levels of network effects.

2. Monolithic Hypertext Systems, Control Choices and Network Effects

Ted Nelson intuitively understood the network effects of hypertext, using utopian rhetoric to describe a global docuverse of hyperlinked information in Literary Machines [Nelson, 1981]. Some engineers heeded Nelson's call to arms and labored to bridge the gap between the Nelson's ideals, and the compromises and limitations of existing computing technology. Some worked directly on Xanadu, while others performed their own interpretations and implementations, leading directly and indirectly to the development of monolithic hypertext systems such as Intermedia [Yankelovich et al., 1988], KMS [Akscyn et al., 1987], HyperCard [Apple, 1987], and StorySpace [Bolter, 1987][Eastgate, 1991].

Monolithic hypertext systems, motivated by a desire to keep their information base internally consistent, and to provide a consistent user interface, have an architecture which tightly controls the data, hypertext structure, and user interface of the system.  Hypertext readers using these systems have a nice user experience with fast link traversals, and no broken links.  Content providers using the monolithic hypertext systems are required to import data into the system, or use system specific editors. Data storage is typically limited to a single file or database (e.g. HyperCard), network file system, or to data storage on a local area network (e.g., KMS), limiting the amount of data which can be accommodated by the system, and preventing distribution of the data across a wide area network.

The choice to control all aspects of the system leads to limited network effects. While readers are attracted to these systems by the rich, highly useful content type provide, the amount and variety of this content is limited.  Due to the need to learn new editors, and because there are relatively few initial readers, content providers do not have a lot of incentive to provide content.  Since there are no provisions for remote access to the hypermedia content, the population of readers is limited to those who have access to the local file system.  Thus, though there was sufficient initial interest from readers of these hypertexts, there was insufficient motivation for content providers to add new information, eventually leading to a lack of interest from readers.  No network effects were generated.

The need to provide incentive for content providers was noted in [Fountain et al., 1990], which states:

The use of hypertext and hypermedia systems is still largely confined to the research community.  This is partly because of the limitations of commercially available systems and partly because of the tremendous effort required to create and maintain a hypertext system.  These issues are compounded by the fact that currently available hypertext packages are basically closed systems, so that if material is created in one system it is very difficult to integrate it with material created in another system. We believe that this is a major barrier to the growth and development of hypertext and hypermedia applications outside the research community. [p. 299]
Hypercard and StorySpace provide some limited exceptions to the lack of network effects for monolithic hypertext systems.  Since HyperCard was freely distributed with Macintosh computers for several years, and HyperCard players are still part of the MacOS, a sufficient base of potential readers existed to provide incentive for development of commercial HyperCard stacks.  The ability to neatly package a hypertext into an easily transportable unit, the stack, also facilitated the development of commercial HyperCard stacks. By adding commercial incentive to produce content, more content was developed for HyperCard than if all content utility depended solely on the number of people reading free content.  However, today the majority of HyperCard content is educational, produced by educators whose job is to produce content for a small collection of readers (their students), and hence do not require the incentive of a large set of readers to derive utility from the content.
StorySpace is another interesting exception.  With StorySpace, content providers use the system as a form of self-expression, and are not motivated primarily by a large readership for their hypertexts, although a commercial market for literary hypertext does exist. The self-expression provides sufficient motivation to produce content, and the value provided by large numbers of readers is not necessary to "prime the pump" to provide incentive for generation of content. Also, given the artistic requirements for total visual control over the hypertext, a monolithic hypertext system best meets the needs of literary hypertext.

3. Open Hypermedia Systems, Control Choices and Network Effects

Open hypermedia systems began as an explicit reaction against the closed nature of monolithic hypertext systems. [Pearl, 89], which describes the first open hypermedia system, begins with a paragraph describing the closed nature of monolithic hypertext systems, and and follows with a paragraph extolling the openness of Sun's Link Service. For most open hypermedia systems (a non-exhaustive list includes DHM [Gronbaek et al., 1993], Hyperform [Wiil, Leggett, 1992], Microcosm [Davis et al., 1992],  Multicard [Rizk, Sauter, 1992], and Chimera [Anderson et al., 1994]), a key quality of openness is the support of the heterogeneous tools which populate a user's computing environment. The rationale for this requirement is generally pragmatic: content is produced by these tools, and they are the locus of work on the computer. To provide hypertext support to the user's environment, hypertext must be brought to the tools, rather than bringing the output of the tools to the hypertext system.

By focusing on adding hypertext functionality to desktop applications, open hypermedia systems consciously relinquish control over the user interface for data in the hypermedia system, and accept the need for an application launcher component to invoke applications as needed to view data after a link traversal. Other control choices vary (for an in-depth description of the various control tradeoffs  in open hypermedia systems, see [Osterbye, Wiil, 1996]). Link server systems maintain control over the hypertext structure, but also relinquish control over the data being linked, allowing it to reside in multiple repositories. Open hyperbase systems control both the hypertext structure and the data being linked, thus providing greater consistency, but requiring applications to use its data repository.

Unlike monolithic hypertext systems, some designers of open hypermedia systems directly considered network effects. [Pearl, 1989], in the conclusion notes:

With an open protocol, the power of each element of a system expands as it interoperates with others.  Open linking can make the power of hypertext available to the world of software.  We hope to see linking, and attendant hypertext capabilities, as much a standard part of the computer desktop as the cutting and pasting of text are today. [p.145]
[Davis et al, 1992], provides a call to arms in its introduction:
The next generation of hypermedia must appear to the user as a facility of the operating system that is permanently available to add information linking and navigation facilities with the minimum amount of user intervention and without subtracting any of the functionality that was previously available. [p. 182]
The analysis of network effects for open hypermedia systems can still be viewed in terms of readers and content providers, but is shifted towards considerations of tool integration because the user interface to the data in the hypermedia system is via pre-existing tools which are generally hypertext unaware. Complicating the analysis is the common lack of a clear distinction between readers and content providers.  Since many open hypermedia systems have little or no separation between reading and authoring, readers and content providers are often the same.

Readers are motivated to use an open hypermedia system because of the hypertext linking between related documents. As noted above in [Pearl, 1989], hypertext linking increases the utility of each application, due to the interoperation provided by hypertext link traversals. Content providers have incentive to add links because they are immediately useful (i.e., they are in data used by the content producer), or can be traversed by other users of the system. The ability to link together data is limited only by the number of hypertext-aware applications. This realization motivates the desire to provide open hypermedia services in the operating system, since pervasive availability of hypermedia services would lead to more hypertext-aware applications.

Open hypermedia systems have many problems that stem directly from not controlling the user interface and not controlling the hyperlinked data, and these problems limit the ability to generate network effects. The editing problem, the data versioning problem, and difficulties with user interface consistency are noted in [Davis et al., 1992]. Add to these the difficulty of configuration management of different versions and types of applications across user environments, and the problem of limited screen real estate after several applications have been launched. Finally, the lack of highly scalable remote data access support in open hypermedia systems is also a noted problem which has spawned much current research.  Altogether, these issues reduce the incentives for readers, and increase the maintenance burden for content providers. The lack of distribution support further caps the total possible number of readers, putting an upper limit on the potential utility of the information. However, even if global distribution was available, the problems inherent in providing hypertext services across widely divergent user machine and application configurations would also limit the utility of these hypertexts for readers.

4. World Wide Web, Control Choices and Network Effects

The Web began as a reaction against an information space very similar to that being touted as ideal by the open hypermedia community. Rather than having to use multiple programs on several computers to access information, the Web aimed at being a unified access point for the information provided by these programs. Slides from a 1993 presentation [Berners-Lee, 1993] describe the concept of universal readership:
Before W3, typically to find some information at CERN one had to have one of a number of different terminals connected to a number of different computers, and one had to learn a number of different programs to access that data. The W3 principle of universal readership is that once information is available, it should be accessible from any type of computer, in any country, and an (authorized) person should only have to use one simple program to access it.
To achieve this goal, the Web made different control tradeoffs from either monolithic or open hypermedia systems, choosing to control the user interface (via the browser) but not controlling either the hypertext structure, or the hypertext data.  The lack of control over the hypertext structure and data allowed these aspects of the system to be massively decentralized. The triad of standards, URL [Berners-Lee et al., 1994], HTTP [Fielding et al., 1997], and HTML [Raggett et al., 1998] provided the foundation for interoperation in a widely distributed, large-scale information space.

With the clarity of hindsight, the Web appears optimally suited for generating network effects.  As the 1993 talk notes:

To allow the web to scale, it was designed without any centralized facility. Anyone can publish information, and anyone (authorized) can read it. There is no central control. To publish data you run a server, and to read data you run a client. All the clients and all the servers are connected to each other by the Internet. The W3 protocols and other standard protocols allow all clients to communicate with all servers.
Since the Web provided a single user interface to existing repositories of information (a valuable interface on the early Web was to the phone book at CERN), as well as hypertext linking from documents which supported HTML, readers had incentive to use the system. For content providers, the Web offers a significant barrier to entry, requiring the installation and configuration of a Web server and, for many providers, initial or improved connection to the Internet. Not surprisingly, the early Web was limited by the small amount of information available, and the fact this information was related almost entirely to high energy particle physics. Two events in 1993 reduced the barriers to entry for both readers and content providers.  First, the NCSA HTTP server was released, and was rapidly ported to most current computing platforms.  Unlike the other existing server, the CERN server, this server could be installed by any user, and did not require super user (root) access, and this allowed installation of Web servers without the need for securing buy-in from typically conservative computing support organizations. Second, the release of the Mosaic browser on Unix, Mac and PC platforms increased the base of potential users, and provided a visually pleasing interface which increased reader's incentives for using the system. While these two events would eventually have touched off the frenzy of growth which categorized the Web in 1994-6, an article in the Business section of the New York Times in December, 1993 [Markoff, 1993] added sufficient new users to jump-start the cycle of increasing network effects, as new readers increased the incentives for content providers, who provided more information, leading to more readers, etc.

By controlling the user interface, the Web is able to provide a single, attractive, easy-to-use entry point into the system. Recognizing that a single application cannot provide viewers for all media types, the typical browser provides launch-only hypertext services to invoke an application which displays the unknown media type, and plug-ins, which allow viewers for unknown types to use the same screen real estate as the browser. If the Web controlled the hypermedia structure, it would have led to a single scalability choke point as increasing numbers of systems accessed the same system for link information. By not placing control requirements on the data displayed by the system, the Web could accommodate a wide range of information repositories, enabling more information providers.

Though the web has its noted drawbacks, with broken links, slow data access, and lack of versioning support being more frequently mentioned problems, it is notable that these problems have not disincentivized readers or content providers sufficiently to cause them to abandon the system, nor did they noticeably dampen the rate of adoption of the Web.

5. Conclusion

This paper described a simple model of how the interaction between information producers (content providers) and consumers (readers) leads to the generation of network effects in hypertext systems.  Three classes of hypertext systems, monolithic, open, and Web are analyzed from the perspective of the control decisions embedded in their architectures, and how these control decisions led to differing levels of network effects.

Although preliminary, the discussion in this paper are suggestive of several points. First, lack of control over the data in a hypermedia system, combined with a large-scale distribution infrastructure is a key aspect of achieving network effects, since this control choice affords large numbers of readers. Examination of network effects from the Web and monolithic hypermedia systems suggests that control over the user interface is a key contributor to network effects, since it incentivizes readers, and allows for more control over the presentation by content providers. Control over the hypermedia structure provides a negative contribution to network effects, since the control point limits scalability, thus capping the total number of readers.


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