The NASA/IPAC Extragalactic Database (NED) is widely acknowledged as the most comprehensive and easy-to-use resource for information about sources populating the Universe beyond our Milky Way galaxy (1) NED is an online research facility designed to support scientists, educators, space missions and observatories in the planning, execution and publication of research on extragalactic objects. The foundation of NED is a growing database of galaxies, quasars and all types of extragalactic objects that can be searched by positions, redshifts, object types, references, authors, and multi-wavelength cross-identifications produced from thousands of catalogs and journal articles. The primary goal of NED is to maintain an up-to-date panchromatic synthesis of basic data for all known (cataloged and published) extragalactic objects, including pointers to the astrophysical literature and to relevant distributed archive resources. Scientists working in observational extragalactic astronomy use NED in their research at nearly every step, from proposal planning, through data collection, data interpretation, publication, and archiving of calibrated images and spectra. Many professors also incorporate NED into their lesson plans. As of the time of writing, over 2,100 articles in the refereed astrophysics literature (Astrophysical Journal, Astronomical Journal, Monthly Notices of the Royal Astronomical Society, Astronomy & Astrophysics, etc.) have acknowledged NED directly as an important tool for the authors' research.
NED consists of these main components: (1) a growing database serving cross-correlated panchromatic data and pointers for millions of extragalactic objects; (2) a Web-based user interface accessible from any Web browser with an Internet connection (as well as legacy VT-100 and X-window versions); (3) support for direct connectivity from remote computer programs and Web sites that function as clients to the NED servers; and (4) an automated batch mode for processing large requests. In this paper we review highlights of each of these areas, outline a case study currently under way that shows how NED is being used in conjunction with linked survey archives to characterize the properties of galaxy classes using machine learning algorithms, and conclude with a discussion of how the capabilities will evolve in support of large-scale data mining applications that can utilize NED in concert with geographically distributed archives. There is insufficient space here for a comprehensive history and complete technical review of NED. A discussion of the motivation, initial design, and early history of NED was given by Helou et al.  Casual users, or those who have not used it in a long time, may think of NED mainly as a `literature' service or `digital library' in which users can only look up information on objects one at a time by catalog entry name, or through article author name searches and the like. In this paper we review the recent and ongoing evolution of NED beyond these classic queries, including support for data exploration and discovery using classes of objects.
1 E.g., Nature, Netguide, October 2000, also available online at http://www.nature.com/netguide Back.