1 Introduction

The Astrophysics Data System (ADS) Abstract Service was originally designed as a search and retrieval system offering astronomers and research librarians sophisticated bibliographic search capabilities. Over time, the system has evolved to include full-text scans of the scholarly astronomical literature and an ever-increasing number of links to resources available from other information providers, taking full advantage of the capabilities offered by the emerging technology of the World-Wide Web (WWW).

As new data and functionality were incorporated in the ADS, the design of its system components evolved as well, driven by the desire to strike a balance between simplicity in the operation of the system and richness in its features. Over time, we favored design approaches promising long-term rewards over short-term gains, within the limits allowed by our resources. The approach we followed in software development has always been very pragmatic and data-driven, in the sense that specialized software components were designed to work efficiently with the existing datasets, rather than attempting to use general-purpose, monolithic software packages.

This paper gives an overview of the architecture of the Astrophysics Data System bibliographic services and discusses in detail the design of the underlying data structures and the implementation of its key software components. In conjunction with three other ADS papers in this volume, it is intended to give a complete description of the current state and capabilities of the ADS. An overview of the history and current use of the system is given in [Kurtz et al. (2000)] (OVERVIEW from here on); details on the datasets in the ADS, their creation and maintenance is given in [Grant et al. (2000)] (DATA); a complete description of the ADS search engine and its user interface is given in [Eichhorn et al. (2000)] (SEARCH).

Section 2 discusses the methodological approach used in the management of bibliographic records, their representation in the system, and the procedures used for data exchange with our collaborators. Section 3 describes the structure of the index files used by the ADS search engine, the implementation of the procedures that create them, and the use of discipline-specific knowledge to improve search results. Section 4 details the design and implementation of general procedures for the creation and management of properties associated with bibliographic records, and their use in the creation of links to internal and external resources. Section 5 discusses the set of procedures used to clone the ADS bibliographic services to the current mirror sites and the level of system independence necessary for their operation. In Sect. 6 we describe how the recent developments in technology and collaborations among astronomical data centers may affect the evolution of the ADS.