The design of previous prototype systems
that provide electronic library services for
image and text retrieval
has been dictated by relatively slow communication technology
(see, for example, the September 1993 issue of the Journal of the American Society
for Information Science).
In particular, the methodology typically makes use of
scanning to obtain digital images to fit current monitors.
The scanning process, however, is inefficient and prone to noise.
To overcome these difficulties the resolution of images are reduced
to fit current monitor screens; and filtering is used
to smooth the reduced images and to remove high-frequency noise.
Furthermore user access to the electronic library is from workstations (and terminals)
using 9600 baud to 56 kp/s transmission lines.
An 
by 
inch page at 
dpi requires in excess of
200 kb. If monitor screens had sufficient resolution,
a page would require 8 seconds to transmit.
Data compression for transmission is
used to bring the transmission time to an acceptable level.
In contrast, the Alexandria Project proposes to make use of the emerging broadband integrated services digital network (B-ISDN) technology [28] to offer a wider range of services to a greater user population with faster access. Broadband transmission is over one of the SONET family of fiber optic channels which are organized into several synchronous hierarchies. STS-3 transmits data at around 155 Mb/s; STS-12 at around 620 Mb/s. Data transport in B-ISDN is according to the asynchronous transfer mode (ATM). Information is segmented into 48 byte cells which are transmitted asynchronously over the broadband channel. The asynchronous nature of access increases the efficiency of channel usage. The bandwidth of B-ISDN systems will lessen the need for data compression for transmission. For example, STS-12 transmits a full 300 dpi page in 0.33 ms and could provide virtually simultaneous service to 100 users with little noticeable delay.
Local users would be connected on a Distributed Queue Dual Bus (DQDB) 802.6 [48] metropolitan area network. Figure 3 depicts the relationship between the users, the network, and the library functions. The term server in this figure is used to signify a generic service function in the digital library system. Examples include catalogue services, remote database access, user query processing.
Figure 3: Network Architecture
The Open Systems Interconnection Model (OSI) of the International Standards Organization [65] divides the functions required for networking into layers. The particular way a system implements a service is not relevant; services need only present a standard interface in order to communicate. To permit communication between electronic libraries, using different query systems, for example, a unified approach to the architecture will be developed.
Scanning has been required in previous prototype systems since there were few direct electronic links from publishers to the libraries. On the other hand, many journals will now accept articles submitted electronically. We will define a system's environment to make it attractive for publishers to directly transmit images/text to the electronic library.
The Alexandria Project makes the data accessible to many users. Thus there is also a need for network security encompassing the issues of privacy, copyright protection and authentication.