The High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center is a multi-mission archive facility supporting the high-energy astrophysics community around the world. HEASARC services include providing, via a variety of user interfaces, access to many different types of data and information including proposals and grants tracking information, astronomical catalogs, observation logs, images, etc.
Previously, most HEASARC information was housed in a home-grown database system, based on that used for EXOSAT. As the HEASARC holdings continued to grow, certain disadvantages of this system began to manifest themselves.
As in any home-grown system, continuity of maintenance became a problem. Adding functionality in terms of enriched metadata to allow more complex or multi-mission data searching was difficult. Further, the older database software had file names and locations directly linked to the metadata, which can cause changes at the lowest levels of the system to have impact throughout.
In addition, other information at the HEASARC and affiliated organizations were kept in separate databases, on different platforms running commercial relational database management system software. There was no well-defined way to communicate between these information repositories. This caused inconvenience both to users who were required to deal with several disparate systems, and to developers who had to create similar functions redundantly for the separate systems. It also caused problems when data and information is transferred between, for example, the HEASARC and the processing facility or the deep archive.
Therefore, the database development efforts at the HEASARC had two main goals: to migrate to a standard commercial database management system, and to facilitate the exchange of information between database systems.
Maintaining and Enhancing Services
As an operational facility, the HEASARC had the obligation to avoid disrupting the level of service it provided to its users. This implied that current user interfaces, or enhanced versions thereof, must continue to be available. The HEASARC currently provides both a command-line interface and a variety of services accessible via the World-Wide Web.
In addition, many HEASARC users have become accustomed to accessing the data files and tables directly via File Transfer Protocol (FTP) and Structured Query Language (SQL) respectively. This type of access must continue to be supported as well.
For maximum flexibility in the support of underlying heterogeneity, both in the types of information within the HEASARC database and in communicating between components of the HEASARC systems and with other organizations, it became clear that what was required was a facility not only for describing data files via entries in tables (catalog level), but also to describe the catalog-level tables themselves in such a way that information could be exchanged about what tables and attributes are available for search. This level in the information hierarchy is what we are calling "meta-information," or the "metabase."
The meta-information design is intended to be as generic as possible. Since the astronomical content in HEASARC's database resides in the catalog-level tables, the meta-information serves the function of describing these tables and the parameters available therein. Therefore, it could theoretically be used to describe information used in any discipline. On a practical level, this at least serves to facilitate the use of data across astrophysics missions which might arrange their information differently.
The requirements analysis was undertaken as the first step in the development of a multi-mission database management system for the High Energy Astrophysics Science Archive Research Center (HEASARC). It was used as a vehicle for discussion and as a springboard for the design effort. It was not intended as a formal specifications document. Neither is it continually updated to reflect the evolution of our thinking during the prototyping and implementation phases of the project. It is included here as a useful summary of our original goals.
The migration of the HEASARC database to a commercial RDBMS (first INGRES, and then later Sybase) was initially completed in 1995, when the HEASARC's World-Wide Web database interface, Browse, was released. The overall architecture and implementation has continuously evolved since then, however.
Documentation prepared by the HEASARC Database Group
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