What do we have to consider in building and distributing databases of
visual materials in a multi-user environment? This presentation examines
a variety of concerns that need to be addressed before a multimedia
database can be set up in a networked environment.
In the past it has not been feasible to implement databases of visual
materials in shared-user environments because of technological barriers.
Each of the two basic models for multi-user multimedia databases has
posed its own problem. The analog multimedia storage model (represented
by Project Athena's parallel analog and digital networks) has required an
incredibly complex (and expensive) infrastructure. The economies of
scale that make multi-user setups cheaper per user served do not operate
in an environment that requires a computer workstation, videodisc player,
and two display devices for each user.
The digital multimedia storage model has required vast amounts of storage
space (as much as one gigabyte per thirty still images). In the past the
cost of such a large amount of storage space made this model a
prohibitive choice as well. But plunging storage costs are finally
making this second alternative viable.
If storage no longer poses such an impediment, what do we need to
consider in building digitally stored multi-user databases of visual
materials? This presentation will examine the networking and
telecommunication constraints that must be overcome before such databases
can become commonplace and useful to a large number of people.
The key problem is the vast size of multimedia documents, and how this
affects not only storage but telecommunications transmission time.
Anything slower than T-1 speed is impractical for files of 1 megabyte or
larger (which is likely to be small for a multimedia document). For
instance, even on a 56 Kb line it would take three minutes to transfer a
1-megabyte file. And these figures assume ideal circumstances, and do
not take into consideration other users contending for network bandwidth,
disk access time, or the time needed for remote display. Current common
telephone transmission rates would be completely impractical; few users
would be willing to wait the hour necessary to transmit a single image at
2400 baud.
This necessitates compression, which itself raises a number of other
issues. In order to decrease file sizes significantly, we must employ
lossy compression algorithms. But how much quality can we afford to
lose? To date there has been only one significant study done of
image-quality needs for a particular user group, and this study did not
look at loss resulting from compression. Only after identifying
image-quality needs can we begin to address storage and network bandwidth
needs.
Experience with X-Windows-based applications (such as Imagequery, the
University of California at Berkeley image database) demonstrates the
utility of a client-server topology, but also points to the limitation of
current software for a distributed environment. For example,
applications like Imagequery can incorporate compression, but current X
implementations do not permit decompression at the end user's
workstation. Such decompression at the host computer alleviates storage
capacity problems while doing nothing to address problems of
telecommunications bandwidth.
We need to examine the effects on network through-put of moving
multimedia documents around on a network. We need to examine various
topologies that will help us avoid bottlenecks around servers and
gateways. Experience with applications such as these raise still broader
questions. How closely is the multimedia document tied to the software
for viewing it? Can it be accessed and viewed from other applications?
Experience with the MARC format (and more recently with the Z39.50
protocols) shows how useful it can be to store documents in a form in
which they can be accessed by a variety of application software.
Finally, from an intellectual-access standpoint, we need to address the
issue of providing access to these multimedia documents in
interdisciplinary environments. We need to examine terminology and
indexing strategies that will allow us to provide access to this material
in a cross-disciplinary way.
Ronald LARSEN Directions in High-Performance Networking for
Libraries
The pace at which computing technology has advanced over the past forty
years shows no sign of abating. Roughly speaking, each five-year period
has yielded an order-of-magnitude improvement in price and performance of
computing equipment. No fundamental hurdles are likely to prevent this
pace from continuing for at least the next decade. It is only in the
past five years, though, that computing has become ubiquitous in
libraries, affecting all staff and patrons, directly or indirectly.
During these same five years, communications rates on the Internet, the
principal academic computing network, have grown from 56 kbps to 1.5
Mbps, and the NSFNet backbone is now running 45 Mbps. Over the next five
years, communication rates on the backbone are expected to exceed 1 Gbps.
Growth in both the population of network users and the volume of network
traffic has continued to grow geometrically, at rates approaching 15
percent per month. This flood of capacity and use, likened by some to
"drinking from a firehose," creates immense opportunities and challenges
for libraries. Libraries must anticipate the future implications of this
technology, participate in its development, and deploy it to ensure
access to the world's information resources.
The infrastructure for the information age is being put in place.
Libraries face strategic decisions about their role in the development,
deployment, and use of this infrastructure. The emerging infrastructure
is much more than computers and communication lines. It is more than the
ability to compute at a remote site, send electronic mail to a peer
across the country, or move a file from one library to another. The next
five years will witness substantial development of the information
infrastructure of the network.
In order to provide appropriate leadership, library professionals must
have a fundamental understanding of and appreciation for computer
networking, from local area networks to the National Research and
Education Network (NREN). This presentation addresses these
fundamentals, and how they relate to libraries today and in the near
future.