1 Introduction

Astronomers today are more prolific than ever before. Studies in publication trends in astronomy ([Abt 1994]; [Abt 1995]; [Schulman et al. 1997]) have hypothesized that the current explosion in published papers in astronomy is due to a combination of factors: growth in professional society membership, an increase in papers by multiple authors, the launching of new spacecrafts, and increased competition for jobs and PIs in the field (since candidate evaluation is partially based on publication history). As the number of papers in the field grows, so does the need for tools which astronomers can use to locate that fraction of papers which pertain to their specific interests.

The ADS Abstract Service is one of several bibliographic services which provide this function for astronomy, but due to the broad scope of our coverage and the simplicity of access to our data, astronomers now rely extensively on the ADS. Other bibliographic services not only link to us, but some have built their bibliographic search capabilities on top of the ADS system. The International Society for Optical Engineering (SPIE) and the NASA Technical Report Service (NTRS) are two such services.

The evolution of the Astrophysics Data System (ADS) has been largely data-driven. Our search tools and indexing routines have been modified to maximize speed and efficiency based on the content of our dataset. As new types of data (such as electronic versions of articles) became available, the Abstract Service quickly incorporated that new feature. The organization and standardization of the database content is the very core upon which the Abstract Service has been built.

This paper contains a description of the ADS Abstract Service from a "data" point of view, specifically descriptions of our holdings and of the processes by which we ingest new data into the system. Details are provided on the organization of the databases (Sect. 2), the description of the data in the databases (Sect. 3), the creation of bibliographic records (Sect. 4), the procedures for updating the database (Sect. 5), and on the scanned articles in the Astronomy database (Sect. 6). We discuss the interaction between the ADS and the journal publishers (Sect. 7) and analyze some of the numbers corresponding to the datasets (Sect. 8). In conjunction with three other ADS papers in this volume, this paper is intended to offer details on the entire Abstract Service with the hopes that astronomers will have a better understanding of the reference data upon which they rely for their research. In addition, we hope that researchers in other disciplines may be able to benefit from some of the details described herein.

As is often the case with descriptions of active Internet resources, what follows is a description of the present situation with the ADS Abstract Service. New features are always being added, some of which necessitate changes in our current procedures. Furthermore, with the growth of electronic publishing, some of our core ideas about bibliographic tools and requirements must be reconsidered in order to be able to take full advantage of new publishing technologies for a new millennium.