son, he and his team developed NLS,
the first working hypertext system with
graphical user interface, mouse, and
collaboration tools.
In the late 1980s, Tim Berners-Lee
created the World Wide Web infrastructure to facilitate information access and as a potential means to implement many of Bush’s, Nelson’s, and
Engelbart’s ideas in the established
worldwide Internet.
While these systems were major
advances in the quest for universal information access, they left unsolved
many of the difficult issues of information management noted earlier.
Our objective here is to show that the
Digital Object Architecture, which has
been under development since the late
1980s at the Corporation for National
Research Initiatives (CNRI) and is now
reaching a tipping point, can provide
the missing pieces of infrastructure
and help us to attain universal information access.
Toward a universal address Space
A universal address space is the most
fundamental element of a system of
universal information access. A collection of ARPA-sponsored projects in the
1960s developed the first methods for
doing this efficiently.
In a famous 1960 article “
Man-computer symbiosis,” J.C.R. Licklider
expounded on the virtues of “
intergalactic networks” and man-machine
communications. Partly at his instigation, MIT’s Project MAC undertook the
construction of an operating system,
Multics, which would be a “computer
utility” that could dispense computing power and information access
widely and cheaply. Other research organizations, such as IBM, UC Berkeley
(Genie), and BBN (Tenex), were early
developers of time-shared operating
systems that could be networked.
Within the Multics system, information sharing was achieved by making virtual memory a common space accessible
by every user on the system. The directory structure was an overlay that let users assign their own symbolic names to
files; files themselves were addressed internally by their virtual addresses. Users
never had to open or close files, or copy
them from secondary storage to their
workspaces; they simply referenced
them as segments of address space.
a universal address
space is the most
fundamental element
of a system of
universal information
access.
Jack Dennis, who helped design the
Multics virtual memory, saw how to
generalize it to allow dynamic sharing
of a more general class of objects, not
just files, and how to protect these objects from access not permitted by their
owners. His “capability architecture”
became the blueprint for object-oriented runtime systems. 2 That architecture
inspired two commercial computing
systems—Plessey 250 and IBM System
38—and two research projects—
Cambridge CAP and CMU Hydra—that contributed much implementation knowledge. These projects all demonstrated
that a large widely accessible address
space would not only facilitate sharing,
but it could be implemented efficiently
on a single machine with a large shared
file system. The capability architecture
also provided a clean way of managing
access and controlling rights by channeling all object references through a
reference monitor protocol. 3
The capability architecture easily
generalized to homogeneous networks
all running the same operating system. Unfortunately, it did not generalize well to the heterogeneous systems
making up the Internet.
In 1970, the ARPANET expanded
the universe of connected systems beyond a single machine to hundreds of
time-shared computers. In the U. S. and
around the world, other packet networks were developed in parallel with
the ARPANET, including, in particular,
a packet satellite network, a ground radio packet network, and various local
area networks, such as token rings and
Ethernet.
The Internet, introduced in 1973 by
Bob Kahn and Vint Cerf, is a global in-
formation system composed of many
networks and computational resourc-
es all embedded within a single large
address space based on the Internet
Protocol (IP) addresses. The domain
name system, introduced in 1983,
maps domain names to IP addresses,
making it much easier for users to ad-
dress computers.
The Digital object architecture
Universal information access was not
achieved in the Internet because none
of the protocols was designed relative
to information-sharing architecture
principles. In the 1980s, prior to the
development of the Web, as part of its
work on digital libraries, CNRI started
designing a system for enabling mobile programs (called “Knowbots”) to
carry out information-access tasks in
a network environment. This led to
the later formulation by CNRI of the
Digital Object Architecture (DOA), 1, 4, 5
which culled out and unified four key