6.1. Abstract and Article Servers
NASA's ADS Abstract Service (adsabs.harvard.edu/abstract_service.html) is offered at the Center for Astrophysics (CfA) of the Smithsonian Astrophysical Observatory (SAO). It goes back to several 105 abstracts prepared by NASA's `` Scientific and Technical Information'' Group (STI) since 1975. Note that the latter abstracts may not be identical with the published ones and that complete coverage of the journals is not guaranteed. Since 1995 most of the abstracts are being received directly from the journal editors, and coverage is therefore much more complete. The service now contains abstracts from four major areas which need to be searched separately: Astronomy (~ 380,000 abstracts), Instrumentation, Physics & Geophysics and LANL/SISSA astro-ph preprints (Section 6.2). The preprints expire 6 months after their entry date. The four databases combined offer over 1.1 million references. The service is also useful to browse contents of recent journals using the BIBCODE QUERY or TOC QUERY (Section 6.5) links. Its popularity is enormous: it was accessed by ~ 10,000 users per month, and about 5 million references per month were returned in response to these queries in late 1997. It has mirror sites in Japan (ads.nao.ac.jp) and France (cdsads.u-strasbg.fr/ads_abstracts.html).
The ADS provides very sophisticated search facilities, allowing one to filter by author, by title word(s) or words in the abstract, and even by object name, albeit with the silent help of NED and SIMBAD. The searches can be tuned with various weighting schemes and the resulting list of abstracts will be sorted in decreasing order of relevance (see adsdoc.harvard.edu/abs_doc/abs_help.html for an extensive manual). Each reference comes with links (if available) to items like (C) citations available (references that cite that article), (D) data tables stored at CDS or ADC, (E) electronic versions of the full paper (for users at subscribing institutions), (G) scanned version of the full paper, (R) references cited by that article, etc. Links between papers (citations and references) are gradually being completed for older papers. Citations are included for papers published since 1981 and were purchased from the ``Institute for Scientific Information'' (ISI), see below. When the recognition of the full text from the scanned images has been completed in a few years (see below), ADS plans to build its own R and C links.
The ADS also employed page scanners to convert printed pages of back issues of major astronomical journals into images (``bitmaps'') accessible from the web. Early in 1995 the ADS started offering this ``Article Service'' at adsabs.harvard.edu/article_service.html. Images of over 60,000 scanned articles are now on line, and over 250,000 pages were retrieved monthly in 1997. The intention is to prepare page scans back to volume 1 for all major journals. Note, however, that these are images of printed pages and not ASCII versions of the full text. Eventually the full article database will be about 500 Gbyte of data. The images of printed pages may eventually be converted into ASCII text via OCR, but currently this exercise is estimated to take a full year of CPU time (excluding the subsequent effort in proof-reading and correcting the OCR result). No full-text search features are available as yet from ADS even for recent articles.
ARIBIB is a bibliographic database with information given in the printed bibliography ``Astronomy and Astrophysics Abstracts'' (AAA) by the Astrononomisches Recheninstitut (ARI) in Heidelberg, Germany. Currently, at www.ari.uni-heidelberg.de/aribib references to the literature of 1983-1997 (Vols. 33-68 of AAA) are freely available, while abstracts may be retrieved only by subscribers of the printed AAA. The ARI intends to prepare abstracts of older literature in a machine-readable format, by scanning earlier volumes of AAA and ``Astronomischer Jahresbericht''.
The UnCover database of authors and titles of scientific papers (see Section 6.5 for details) may also be used for keyword searches, although it does not offer abstracts.
There are numerous well-established commercial bibliographic database services which charge for access. The use of these systems in astronomy has been reviewed by Davenhall (1993) and [Michold et al. (1995)], and [Thomas (1997)] gives a more general overview. Typically these databases cover a range of scientific and engineering subjects and none of them is specifically astronomical. This has the disadvantage that more obscure astronomical journals are not covered, but the advantage that astronomical papers in non-astronomical publications will be included. The Institution of Electrical Engineers (IEE) in the UK produces INSPEC (www.iee.org.uk/publish/inspec) which is the main English-language commercial bibliographic database covering physics (including astrophysics), electrical engineering, electronics, computing, control and information technology. It currently lists some 5 million papers and reports, with over 300,000 new entries being added per year, and it covers the main astronomical journals. An abstract is usually included for each entry. Another important bibliographic database is the Science Citation Index (SCI) produced by the Institute for Scientific Information Inc. (ISI; www.isinet.com) in USA. The SCI contains details drawn from over 7500 journals and (via the Index to Scientific and Technical Proceedings, ISTP) over 4200 conferences per year. While the SCI does not contain abstracts, it offers cross-references to all the citations in each paper that is included, a unique and extremely valuable feature. Often commercial bibliographic services are not accessed directly, but rather through a third-party vendor. Typically such a vendor will make a number of bibliographic databases available, having homogenized their appearance and customized their contents to a greater or lesser extent. There is a number of such vendors; one example is the ``Scientific and Technical Information Network'' (STN; www.cas.org/stn.html) which includes links to about 200 databases.