Speculations on the Future of FITS
Donald C. Wells · ASPC · 1997
The history and philosophy of FITS are reviewed, with emphasis on the lessons-learned and on the archival requirements. Opinions are offered on the likely outcome of current FITS negotiations, such as the year-2000 problem and the WCS proposal, and on possible subjects of future data interchange format negotiations in astronomy. BINTABLE schemas in third-normal-form are advocated. The long-term importance of the BINTABLE format as a platform for future layered-convention agreements is stressed. 1. On the Philosophy of FITS (Lessons-learned) FITS [Flexible Image Transport System] provides a common canonical language for talking about astronomical data structures and, as such, it has a profound positive influence on software design practice in astronomy. By negotiating FITS as a family of similar data formats, Basic-FITS (1979), random-groups (1980), generalized extensions (1983), TABLE (1984), BINTABLE (1991) and IMAGE (1992), we have minimized the negotiation, documentation and training costs for our community. Our most effective negotiating strategy has been to try to achieve bi-lateral agreements. We include “escape hatches” in our agreements, in places where we expect to negotiate future agreements. The history of FITS shows that it is not possible to fully transmit meanings. Instead, the purpose of FITS is agree on the syntax of a language for talking about astronomical data, and to agree on the semantics in only a limited range of cases. Agreement on syntax permits basic portability and interchange of data, and the users are able to bridge the semantic gaps. Newcomers to FITS often ask: “Why doesn’t FITS have a VERSION keyword?” Our answer is: “It does, but the value is always 1.0 by default.” The point is that the introduction of a VERSION code would be incompatible with the use of FITS as an archival format, because designers of new software would be tempted to support only recent versions. The FITS committees will never knowingly obsolete existing conforming FITS files. This policy is often summarized as “once FITS, always FITS.” Seventeen years of production experience with FITS have demonstrated that only a few actual mistakes were made in the design of Basic-FITS, and that they have not hurt us (yet). A minor mistake is that we specified keyword 1The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.