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324 Although there will probably be considerable dupli- cation of software development over the next few years, an active committee with the cooperation of the National Centers could result in the availability of a standard baseline of software by the mid-1980's. If the program- mers have done a good job, the software will be accepted and used by the community, leading to gradual development and (more importantly) acceptance of community-wide software and data-format standards. VI. DATA ARCHIVING Data archives (usually in the form of plate collections) have traditionally been exceedingly valuable in advancing astronomical research. A recent example is the determi- nation of historical light curves of optical objects identified with newly discovered x-ray sources. Such data have not only assisted with the identifications but have also provided valuable clues to the nature of the x-ray sources. As another example, where would we be today without ready access to the Palomar Sky Survey? The large volume of digital images that will be produced in the coming years provides a valuable resource for future generations of astronomers and should be archived. There is more to archiving than simply storing the data. There must be a means for users of the archives to locate data stored in the archives quickly and easily. Not only must the user be able to search indices to deter- mine the availability of images containing the objects of interest to him or her, but in addition, the user must have a means of viewing the images identified by the index search to determine if they are appropriate for the intended research program. Finally, archives should provide protection against data degradation or loss. At present, the only available archival medium suit- able for storing the volume of data described in the previous section is the high-density magnetic tape. However, tapes have several disadvantages. Tape archives must be a manually operated system and are subject to error. The access functions are cumbersome to perform with tape archives. ing the shelf life of tapes. And there is some question concern- In the near future (1982-1983), video disks are expected to become available and promise to revolutionize mass storage systems. Estimates are that initially a read-write unit will cost about $150,000; a read unit,
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325 approximately $50,000; and the disk, about $1,000. eral years after their introduction, the costs are expected to drop to around $50,000, $6,000, and $100, respectively. Video disks are about the size of an ordinary phonograph album and will initially have capacities of 101 bits per disk increasing to 1012 bits per disk after they have been on the market for a few years. Video disks will also facilitate wide dis- tribution of selected data bases. From an original disk it will be possible to make a die that is then used to press multiple copies of the original disk in much the same way that phonograph records are reproduced. For the immediate future, we expect that digital image data will continue to be archived as part of individual astronomers' private tape collections. This is unfor- tunate, because such data are often not preserved for future generations of astronomers. However, when video disks (or other suitable media) become available, funds should be provided to establish formal archives. This process should start slowly so that we gain some experi- ence before making too many mistakes. In particular, one of the National Astronomy Centers should take the lead in developing and implementing an archive. Once the problems are understood, archives can be implemented at other National Centers and then at other major observatories. These implementations should be coordinated by a perma- nent committee, perhaps the same committee suggested in the previous section. Some of the major problems that must be solved are questions of policy rather than tech- nical problems. In particular, it must be recognized that data obtained with public funds are public property and, after a reasonable period following the original observations, must be made available to all qualified users. An important role of the committee will be to promote discussions of these kinds of policy questions throughout the astronomical community. In addition to hardware acquisition, implementation of archives will require some software development (although commercially available data-base-management systems may provide most of the necessary capabilities). Thus the cost of establishing the first archives may be expected to be on the order of $300,000 with the cost of later archives approximately $200,000. In addition, operation of the archives will orobablv require the services of one _ , ~ or two full-time employees to oversee deposition of data into the archives and to fulfill requests for data from the archives. Thus we estimate that for expenditures of