1. Control Choices and Network Effects in Hypertext Systems
Jim Whitehead
Univ. of California, Irvine
Hypertext’99
February 21-25, 1999

2. Control Choices and Network Effects in Hypertext Systems
Network effects are an important (perhaps the primary) adoption factor for hypertext systems
Control choices in the architecture of a hypertext system directly affect its ability to generate network effects.
control of data
control of hypertext structure
control of user interface
Motivation for this investigation was the result of reflecting on the success of the Web.
Why was the Web so widely adopted?
Did the Web’s architecture contribute to its success?
If so, what are the key architectural choices?
What lessons can be learned by examining the Web?
The diversity of hypertext system architectures provides the opportunity to explore the interaction of architecture and adoption.
Perhaps the Web can offer some insight into how a next-generation global hypermedia system should be constructed so it can have a similar adoption dynamic. Does the Web provide lessons on how to replace it?

3. Network Effects
An item possesses network effects when the utility of an item increases with the number of other users of that item.
Has network effects: telephone system system
No network effects: breakfast cereal
Different from scale effects where cost decreases as volume increases
Breakfast cereal does have scale effects

4. Direct and Indirect Network Effects
When the utility of the item depends directly on the number of other people using it
Telephone system
Indirect network effects
An artifact intermediates between an item and the effect of the number of people using the item
Computer hardware and compatible software
Known as “hardware/software” systems
Hypertext systems are hardware/software systems (viewer is “hardware”, content is “software”)

5. Direct Network Effects
Utility
Personal utility is the weighted sum of the utility of each communications path with existing users.
Demand
A person has demand for a system if the personal utility of using the system is greater than or equal to its price.
Source: Rohlfs, J. “A theory of interdependent demand for a communications service” Bell J. of Economics 5(1), 1974.
But, it’s important to note that for most current computer users, the price of the Web is the cost of getting connected to the Internet. For people who already have Internet connections, the “price” is very low, the cost of learning the tool.

6. Direct Network Effects (2)
Any system starts with no users.
When all people who have demand for a system at a given price are using that system, it has reached equilibrium.
… But there are many paths to equilibrium.

7. A Model of Network Effects in Hypertext Systems
In hypertext systems, network effects are generated via the interaction of:
Information producers (content providers)
Information consumers (readers)
Producers and consumers have different utility functions, but both act to maximize their utility from using the system.

8. Hypertext User Utility
Reader utility:
Derived from the amount of information and services available on that system.
Content provider utility:
Derived from the number of people who read documents or use services offered by the content provider.

9. Feedback Loops
Simple feedback loops lead to increases in readers and content providers.
Readers are lured to the system to take advantage of the content and services offered by the hypertext system (readers create a demand-pull for content)
Content providers are attracted to the system to have readers view their content (content providers create a supply-push for readers)
Content entices readers, readers attract content, and so on… a virtuous cycle.

10. Control Choices
Each class of hypertext system made different control choices in its architecture:
Monolithic: control user interface, hypertext structure, and data
Open Hypermedia: control hypertext structure and data, but do not control user interface (each cooperating application has its own UI)
Web: control user interface, but do not control hypertext structure or data

11. Network Effects for Monolithic Systems (1)
The choice to control all aspects of the system leads to limited network effects.
Readers: Attracted to these systems by the rich, highly useful content, but the amount and variety of this content is limited.
Content providers: Due to the need to learn new editors, and because there are relatively few initial readers, little incentive to provide content.

12. Network Effects for Monolithic Systems (2)
Bounded reader population:
Lack of remote access to content limits readers to those who have access to the local file system.
Bounded content provider utility:
Bounded population of readers limits content provider utility, while need to learn new tools increases cost, leading to low motivation for content providers to add new information.
Eventually leads to a lack of interest from readers.
Low generation of network effects.

13. Network Effects for Open Hypermedia Systems (1)
Readers:
Drawn to individual applications in order to access documents within the system.
Motivated to use open hypermedia capabilities to gain advantage of key OHS feature: inter-application hypertext linking
Content providers:
Have incentive to add links because they are immediately useful to provider and other users
The ability to link together data is limited only by the number of hypertext-aware applications.

14. Network Effects for Open Hypermedia Systems (2)
Several known problems with open hypermedia systems:
Editing problem, versioning, lack of user interface consistency, limited screen real estate, etc.
Problems limit network effects:
Reduce incentives for readers
Increase the maintenance burden for content providers.
Limited distribution support caps the total possible number of readers.

15. Network Effects and the Web (1)
Reader utility:
Provided by large amount of documents and services available via the Web
HTML provides visually pleasing displays
Content provider utility:
Early-on, Web provided gateways to existing information sources (gopher, FTP, etc.)
HTML provides control over appearance of information

16. Network Effects and the Web (2)
Control user interface:
Provides a single, attractive, easy-to-use entry point into the system.
No control of hypermedia structure:
Allows hypertext to grow without scalability limits.
No control on hypermedia data:
Accommodates a wide range of information stores (e.g., databases, document management systems), enabling more information providers.

17. Conclusions (1) Scalability problems limit network effects generation
caps on readers  caps on provider utility  arrests path to equilibrium
Scalability-limiting control choices:
Data control: tight control over data creates a data access chokepoint
Hypermedia structure control: tight control over hypermedia structure creates a link traversal & creation chokepoint
Global hypermedia equilibrium will have hundreds of millions of users.
An important implementation note related to data control is that the Web (NCSA server, Apache server) easily allowed all users on a Unix system to contribute content, while a Gopher server only allowed the super user to contribute content.

18. Conclusions (2)
Control over the user interface increases reader and content provider utility.
It incentivizes readers due to visually pleasing displays
Allows for more control over the presentation by content providers
Designers need a lot of control over presentation
Increased utility creates greater demand, more adoption, more network effects
However, don’t control too much: Gopher pitfall
The Web browser controls some aspects of the user interface, but leaves other aspects free.
Navigational elements are controlled, such as link traversal semantics, displaying the URL of the destination of a link, and the very important back button. Hot list of links.
But, the Web doesn't control the layout of each individual page. Gopher was a lot more controlling in this area.