The Astrophysics Data System (ADS) provides access to astronomical bibliographic information, including references, abstracts, and full journal articles, as well as links to other online information sources like online electronic journals and online data. The ADS has two major parts, the abstract service and the online journal articles.
The abstract service provides access to abstracts and references of most of the astronomical literature since 1975. The references are accessible in three databases: Astronomy, Space Instrumentation/Optics, and Physics/Geophysics. As of January 1997, the astronomy database contains almost 300,000 references, the instrumentation database has almost 500,000 references, and the physics database about 250,000 references. The astronomy database includes the bibliography from the Lunar and Planetary Institute from 1978 till 1993. It also includes abstracts and references from journals like Meteoritics and Icarus.
The databases can be searched with a sophisticated search engine, allowing fielded searches http://adsabs.harvard.edu/abstract_service.html. The retrieved references are ranked according to their relevance to the query, taking into account word frequencies for weighting. The search fields are the authors, title, abstract and object names where available. The search engine can search not only for individual words but also for sequences of words. This allows, for instance, a search for "black hole" as a phrase, rather than searching for "black" and "hole" separately.
The database is indexed so that retrieval of abstracts that contain synonyms for the search words (e.g., M31 and Andromeda) is possible. The list of synonyms was compiled manually taking into consideration expert knowledge of the technical language used in astronomy. This synonym list has proven to be one of the most valuable assets of the ADS because it greatly improves the quality of the searches.
For example, type "Jupiter Io torus" in the title search field when you have connected to the ADS Abstract Service. The result of a search is a list of references. The list contains the bibliographic code, authors, title, publication date, score, and a list of links. These links allow access to the abstracts of the articles, the full articles where available, as well as other information. One of the links provides access for selected journal articles to the list of references in these articles and the list of articles that cite this article. (Click the first selection on the Query Results list)
The following links, anchored to the specified letters, are currently available:
A: Abstract provided by NASA/STI.
O: Original author abstract provided by the journal or author.
F: Full article available through the ADS article service as scanned images.
E: Online electronic version of the journal article, usually at the site of the publisher. Access to the electronic version may be restricted to subscribers of the journal.
P: PDF version of the article. This too may be restricted to subscribers of the journal.
D: Online data from the reference in electronic format.
S: List of astronomical objects referred to in the article (provided by the SIMBAD database).
M: The article can be mail-ordered from a document delivery service. This service is fee based and is handled directly through the document delivery service.
I: Additional information about the article provided by the author.
R: List of references for this article. It generally includes only the references to other journal articles.
C: List of references that cite this article.
T: Table of contents for this reference (for books and proceedings volumes).
The ADS abstract service has seen rapid growth since the introduction of the WWW interface. In February 1997 the ADS was accessed from more than 10,000 hosts. This translates into many more users since many hosts (especially hosts of Internet access providers) are used by more than one individual. These users made over 200,000 queries and retrieved 3.9 million references.
The ADS article service provides access to scanned images of full journal articles. We have agreements with the following publications to scan their journals and make them available online a certain time after publication:
Astronomical Journal (USA)
Astrophysical Journal (USA)
Astronomy & Astrophysics (Germany)
Baltic Astronomy (Lithuania)
Bulletin of the Astronomical Society of India (India)
Contributions of the Astronomical Observatory Skalnate Pleso
Monthly Notices of the Royal Astronomical Society (Great Britain)
Publications of the Astronomical Society of Australia (Australia)
Publications of the Astronomical Society of Japan (Japan)
Publications of the Astronomical Society of the Pacific (USA)
Revista Mexicana de Astronomia y Astrofisica (Mexico)
Our scanning is not yet complete as of February 1997. We have scanned 700,000 pages so far and have about 400,000 pages on line. About 200,000 pages are waiting to be scanned. We are also discussing similar arrangements with other journals, including Meteoritics, Icarus, and JGR Planets.
The journals were scanned with a resolution of 600 dots per inch (dpi). This provides very-high-quality images. Printed with a 600 dpi printer, they are almost indistinguishable from the original. The images are stored on our server in two resolutions (200 dpi and 600 dpi). This allows the fast retrieval of a smaller, lower-resolution version. A screen-view version (100 dpi, anti-aliased grayscale) is produced on demand.
In order to provide better service to non-U.S. users, we are trying to duplicate our database in different places. We currently have mirrors at the CDS in France and the Astronomical Data Analysis Center (NAO) in Tokyo, Japan. This greatly improves access times from Europe and East Asia.
In the near future we plan to complete the scanning of the astronomical literature from 1975 to the present. There are still several important journals in the planetary and solar system sciences that have not given us permission to scan their journal. We hope to receive permission from them to complete the digital library in Astronomy. In the longer term we hope to scan the historical literature as well. This is a much larger and more complicated effort and needs to be done in cooperation with the traditional astronomy libraries.
We are currently working with the publisher of the IAU Circulars and the Minor Planet Center to include their publications in the ADS. These would be included as soon as they are published (within less than an hour).
The ADS Homepage is at http://adswww.harvard.edu. The abstract service can be accessed from http://adsabs.harvard.edu/ads_abstracts.html. This form has links to both the primary site at SAO and to the mirrors in France and Japan. The ADS can be contacted by sending e-mail to email@example.com.
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