  Large digital sky surveys, over a broad range of wavelengths, both from the
ground and from space observatories, are becoming a major source of
astronomical data. Some examples include the Sloan Digital Sky Survey (SDSS)
and the Digital Palomar Observatory Sky Survey (DPOSS) in the visible, the
Two-Micron All-Sky Survey (2MASS) in the near-infrared, the NRAO VLA Sky Survey
(NVSS) and the Faint Images of the Radio Sky at Twenty centimeters (FIRST) in
the radio. Many others surveys are planned or expected, in addition to the
previously named surveys. While most surveys are exclusively imaging,
large-scale spectroscopic surveys also exist. In addition, a number of
experiments with specific scientific goals, e.g., microlensing surveys for
MACHOs, searches for near-Earth asteroids, are generating comparable data
volumes. Typical sizes of resulting data sets (as of the late 1990's) are in
the range of tens of Terabytes of digital information, with detections of many
millions or even billions of sources, and several tens of parameters measured
for each detected source. This vast amount of new information presents both a
great scientific opportunity and a great technological challenge: how to
process, and calibrate the raw data; how to store, combine, and access them
using modern computing hardware and networks; and how to visualize, explore and
analyses these great data sets quickly and efficiently.
