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}}
The '''SAO/NASA Astrophysics Data System''' ('''ADS''') is a [[digital library]] portal for researchers on [[astronomy]] and [[physics]], operated for [[NASA]] by the [[Smithsonian Astrophysical Observatory]]. ADS maintains three bibliographic collections containing over 15 million records, including all [[arXiv]] e-prints.<ref>{{Cite web |title=About ADS |url=https://ui.adsabs.harvard.edu/about/ |access-date=2024-07-20 |website=ui.adsabs.harvard.edu}}</ref> Abstracts and full-text of major astronomy and physics publications are indexed and searchable through the portal.
The '''SAO/NASA Astrophysics Data System''' ('''ADS''') is an [[online database]] of over 16 million papers developed by the [[National Aeronautics and Space Administration]] (NASA) on [[Astronomy & Astrophysics|astronomy]] and [[physics]]. [[abstract (summary)|Abstracts]] are freely available for most articles, and fully scanned articles may be available in [[Portable Document Format]] (PDF). Hosted papers may be from [[peer review]]ed and/or non-peer-reviewed sources. ADS is managed by the [[Smithsonian Astrophysical Observatory]].
==Historical context==
Since its beginning in 1992, ADS is a powerful research tool that has significant impact on the efficiency of astronomical research.<ref name="announcement">{{cite journal |last=Kurtz |first=M.J. |display-authors=et al. |year=1993 |title=Intelligent Text Retrieval in the NASA Astrophysics Data System |journal=Astronomical Data Analysis Software and Systems II |volume=52 |page=132 |bibcode=1993ASPC...52..132K}}</ref> ADS also significantly reduces the time required for literature searches by being customized specifically for astronomical needs. Studies have found that the monetary benefit to astronomy that ADS contributes is equivalent to several hundred million in [[USD|US dollars]] every year (2005).<ref name="overview" /><ref name="impact">{{cite journal |last=Kurtz |first=M.J. |author2=Eichhorn G. |author3=Accomazzi A. |author4=Grant C.S. |author5=Demleitner M. |author6=Murray S.S. |year=2005 |title=Worldwide Use and Impact of the NASA Astrophysics Data System Digital Library |journal=Journal of the American Society for Information Science and Technology |volume=56 |issue=1 |pages=36–45 |arxiv=0909.4786 |bibcode=2005JASIS..56...36K |doi=10.1002/asi.20095 |s2cid=15181632}} ([http://cfa-www.harvard.edu/~kurtz/jasis-abstract.html Preprint])</ref>
[[Johann Friedrich Weidler]] published the first comprehensive history of astronomy in 1741 and the first astronomical bibliography in 1755. This was an effort to archive and classify earlier astronomical knowledge and works.
This effort was continued by [[Jérôme Lalande|Jérôme de La Lande]] who published his ''Bibliographie astronomique'' in 1803, a work that covered the period from 480 BCE to the year of publication.
The '''SAO/NASA Astrophysics Data System''' ('''ADS''') usage statistics can be used to analyze global trends in astronomical research due to it being used amongst astronomers worldwide. Those statistics revealed the direct correlation between both the number of astronomers and the amount of research an astronomer carries out and the per capita [[gross domestic product]] (GDP) of the country from where the scientist is based.
The importance of recording and classifying earlier astronomical knowledge and works was recognized in the 18th century, with [[Johann Friedrich Weidler]] publishing the first comprehensive history of astronomy in 1741 and the first astronomical bibliography in 1755. This effort was continued by [[Jérôme Lalande|Jérôme de La Lande]], who published his ''Bibliographie astronomique'' in 1803, a work that covered the time from 480 B. C. to the year of publication. The ''Bibliographie générale de l’astronomie, Volume I and Volume II'' , published by J.C. Houzeau and A. Lancaster in Brussels, followed in the 1882 tountil 1889 period.<ref>{{cite book |last1=Houzeau |first1=J. C. |title=Bibliographie générale de l'astronomie |date=1887 |publisher=F. Hayez, Imprimeur de L'Académie Royale de Belgique |url=https://books.google.com/books?id=xJhA9noqjT0C&q=Bibliographie+g%C3%A9n%C3%A9rale+de+l%27astronomie+volume+I |language=fr}}</ref><ref>{{cite book |last1=Houzeau |first1=Jean-Charles |title=Bibliographie générale de l'astronomie ou catalogue méthodique des ouvrages, des mémoires et des observations astronomiques publiés depuis l'origine de l'imprimerie jusqu'en 1880: Mémoires et notices insérés dans les Collections académiques et les Revues |date=1882 |url=https://books.google.com/books?id=GzxeAAAAcAAJ |language=fr}}</ref> ▼▲The importance of recording and classifying earlier astronomical knowledge and works was recognized in the 18th century, with [[Johann Friedrich Weidler]] publishing the first comprehensive history of astronomy in 1741 and the first astronomical bibliography in 1755. This effort was continued by [[Jérôme Lalande|Jérôme de La Lande]], who published his ''Bibliographie astronomique'' in 1803, a work that covered the time from 480 B. C. to the year of publication. The ''Bibliographie générale de l’astronomie, Volume I and Volume II'' published by J.C. Houzeau and A. Lancaster in Brussels, followed in the 1882 to 1889 period.<ref>{{cite book |last1=Houzeau |first1=J. C. |title=Bibliographie générale de l'astronomie |date=1887 |publisher=F. Hayez, Imprimeur de L'Académie Royale de Belgique |url=https://books.google.com/books?id=xJhA9noqjT0C&q=Bibliographie+g%C3%A9n%C3%A9rale+de+l%27astronomie+volume+I |language=fr}}</ref><ref>{{cite book |last1=Houzeau |first1=Jean-Charles |title=Bibliographie générale de l'astronomie ou catalogue méthodique des ouvrages, des mémoires et des observations astronomiques publiés depuis l'origine de l'imprimerie jusqu'en 1880: Mémoires et notices insérés dans les Collections académiques et les Revues |date=1882 |url=https://books.google.com/books?id=GzxeAAAAcAAJ |language=fr}}</ref>
As the number of astronomers and astronomical publications grew, bibliographical efforts became institutional tasks, first at the [[Royal Observatory of Belgium|Observatoire Royal de Belgique]], where the ''Bibliography of Astronomy'' was published from 1881 to 1898, and then at the [[Astronomical Calculation Institute (Heidelberg University)|Astronomischer Rechen-Institut]] in Heidelberg, where the yearly ''Astronomischer Jahresbericht'' was published from 1899 to 1968;. afterAfter this1968, date itthis was replaced by the yearly [[Astronomical Calculation Institute (Heidelberg University)|''Astronomy and Astrophysics Abstracts'']] yearly book series, which continued until the end of the 20th century.
During the 1980s, however, astronomers realized that the nascent technologies which formed the basis of the [[Internet]] could eventually be used to build an electronic indexing system of astronomical research papers, which could eventually allow astronomers to make extensive searches of the existing literature on any given research topic, as well as to keep abreast of a much greater range of research.<ref name="overview2">{{cite conference |last=Good |first=J.C. |year=1992 |chapter=Overview of the Astrophysics Data System (ADS) |title=Astronomical Data Analysis Software and Systems I |series=ASP Conference Series |volume=25 |editor1=Diana M. Worrall |editor2=Chris Biemesderfer |editor3=Jeannette Barnes |pages=35 |bibcode=1992ASPC...25...35G}}</ref>
The first suggestion of a digital database of journal paper abstracts was made at a conference on ''Astronomy from Large Data-Bases'' held in [[Garching bei München]] in 1987.<ref>{{cite journal |last1=Squibb |first1=G.F. |last2=Cheung |first2=C.Y. |year=1988 |title=NASA astrophysics data system (ADS) study |journal=European Southern Observatory Conference and Workshop Proceedings |volume=28 |page=489 |bibcode=1988ESOC...28..489S}}</ref><ref>{{cite conference |last1=Adorf |first1=H.-M. |last2=Busch |first2=E.K. |year=1988 |title=Intelligent access to a bibliographical full text data base |volume=28 |page=143 |bibcode=1988ESOC...28..143A |journal=European Southern Observatory Conference and Workshop Proceedings}}</ref><ref>{{cite conference |last=Rey-Watson |first=J.M. |year=1988 |title=Access to astronomical literature through commercial databases |volume=28 |page=453 |bibcode=1988ESOC...28..453R |journal=European Southern Observatory Conference and Workshop Proceedings}}</ref><ref>{{cite conference |last1=Rhodes |first1=C. |last2=Kurtz |first2=M.J. |last3=Rey-Watson |first3=J.M. |year=1988 |title=A library collection of software documentation specific to astronomical data reduction |volume=28 |page=459 |bibcode=1988ESOC...28..459R |journal=European Southern Observatory Conference and Workshop Proceedings}}</ref>
TheAn firstinitial suggestionversion of ADS, with a database consisting of journal40 paper abstractspapers, was madecreated atas a conference on ''Astronomy from Large Data-Bases'' held in [[Garchingproof beiof Münchenconcept]] in 19871988.<ref>{{cite journalThe |last1=Squibb |first1=G.F. |last2=Cheung |first2=C.Y. |title=NASA astrophysics data system (ADS) studyAbstract |journal=EuropeanService Southernbecame Observatoryavailable Conferencefor andgeneral Workshopuse Proceedingsvia |year=1988proprietary |volume=28 |page=489 |bibcode=1988ESOC...28..489S}}</ref><ref>{{cite conference |last1=Adorf |first1=H.-M. |last2=Busch |first2=E.K. |title=Intelligent access to a bibliographical full text data base |journal=European Southern Observatory Conference and Workshop Proceedings |year=1988 |volume=28 |page=143 |bibcode=1988ESOC...28..143A}}</ref><ref>{{cite conference |last=Rey-Watson |first=J.M. |title=Access to astronomical literature through commercial databases |journal=European Southern Observatory Conference and Workshop Proceedings |year=1988 |volume=28 |page=453 |bibcode=1988ESOC...28..453R}}</ref><ref>{{cite conference |last1=Rhodes |first1=C. |last2=Kurtz |first2=M.J. |last3=Rey-Watson |first3=J.M. |title=A library collection ofnetwork software documentationin specificApril to astronomical data reduction |journal=European Southern Observatory Conference1993, and Workshopit Proceedingswas |year=1988 |volume=28 |page=459 |bibcode=1988ESOC...28..459R}}</ref> Initial development of an electronic system for accessing astrophysical abstracts took place during the following five years. In 1991 discussions took place on howconnected to integrate ADS with the [[SIMBAD]] database,a containingfew allmonths availablelater. catalogIn designationsearly for1994 objectsthe outsideADS theweb-based [[Solarservice System]]was launched, towhich createeffectively aquadrupled systemthe wherenumber astronomersof couldactive searchusers for allin the papersfive writtenweeks about afollowing givenits objectintroduction.<ref name="overview">{{cite journal |last=Kurtz |first=M.J. |author2=Eichhorn G. |author3=Accomazzi A. |author4=Grant C.S. |author5=Murray S.S. |author6=Watson J.M. |year=2000 |title=The NASA Astrophysics Data System: Overview |journal=Astronomy and Astrophysics Supplement Series |volume=143 |issue=1 |pages=41–59 |doiarxiv=10.1051astro-ph/aas:20001700002104 |bibcode=2000A&AS..143...41K |arxivdoi=astro-ph10.1051/0002104aas:2000170 |s2cid=17583122}}</ref>
In 2011 the ADS launched ADS Labs Streamlined Search which introduced [https://www.researchgate.net/publication/228582891_Retrieval_from_facet_spaces facets] for query refinement and selection. In 2013 , ADS Labs 2.0 started featuring a new search engine, full-text search functionality, scalable facets , and an API was introduced. In 2015 , the new ADS, codenamedcode-named Bumblebee, was released as ADS-beta. The ADS-beta system features a microservicesmicro-services API and client-side dynamic page loading served on a cloud platform. In May 2018 the beta label was dropped and Bumblebee became the default ADS interface—with some legacy features (ADS Classic) remaining available.<ref>{{Cite conference |last1=Accomazzi |first1=Alberto |last2=Kurtz |first2=Michael J. |last3=Henneken |first3=Edwin |last4=Grant |first4=Carolyn S. |last5=Thompson |first5=Donna M. |last6=Chyla |first6=Roman |last7=McDonald |first7=Steven |last8=Shaulis |first8=Taylor J. |last9=Blanco-Cuaresma |first9=Sergi |last10=Shapurian |first10=Golnaz |last11=Hostetler |first11=Timothy W. |last12=Templeton |first12=Matthew R. |last13=Lockhart |first13=Kelly E. |date=January 2018 |title=ADS Bumblebee comes of age |conference=231st Meeting of the American Astronomical Society |at=362.17 |bibcode=2018AAS...23136217A}}</ref> Development continues to the present day, with an extensible [[API]] available: enabling users to build their own utilities on top of the ADS bibliographic record. ▼An initial version of ADS, with a database consisting of 40 papers, was created as a [[proof of concept]] in 1988. The ADS Abstract Service was announced in November 1992 <ref name='announcement' /> and was released for general use in April 1993. The ADS database was successfully connected with the SIMBAD database in the summer of 1993. The creators believed this was the first use of the Internet to allow simultaneous querying of transatlantic scientific databases. Until 1994 the service was available via proprietary network software, but it was transferred to the nascent [[World Wide Web]] early that year. The number of users of the service quadrupled in the five weeks following the introduction of the ADS web-based service.<ref name="overview" />
The ADS service is distributed worldwide , with twelve [[Web mirror|mirror sites]] in twelve countries on five continents,and with the database synchronized by means of weekly updates using [[rsync]], a mirroring utility which allows updates to only the portions of the database which have changed. All updates are triggered centrally, but they initiate scripts at the mirror sites which "pull" updated data from the main ADS servers.<ref name="architecture">{{cite journal |last1=Accomazzi |first1=A. |last2=Eichhorn |first2=G. |last3=Kurtz |first3=M.J. |last4=Grant |first4=C.S. |last5=Murray |first5=S.S. |year=2000 |title=The NASA Astrophysics Data System: Architecture |journal=Astronomy and Astrophysics Supplement Series |volume=143 |issue=1 |pages=85–109 |doi=10.1051/aas:2000172 |bibcode=2000A&AS..143...85A |arxiv=astro-ph/0002105 |s2cid=7182316}}</ref> ▼At first, the journal articles available via ADS were [[Image scanner|scan]]ned [[bitmap]]s created from the paper journals, but from 1995 onwards, the ''[[Astrophysical Journal]]'' began to publish an on-line edition, soon followed by the other main journals such as ''[[Astronomy and Astrophysics]]'' and the ''[[Monthly Notices of the Royal Astronomical Society]]''. ADS provided links to these electronic editions from their first appearance. Since the year 1995, the number of ADS users has doubled roughly every two years. ADS now has agreements with almost all astronomical journals, who supply abstracts. Scanned articles from as far back as the early 19th century are available via the service, which now contains over eight million documents.
▲In 2011 the ADS launched ADS Labs Streamlined Search which introduced [https://www.researchgate.net/publication/228582891_Retrieval_from_facet_spaces facets] for query refinement and selection. In 2013 ADS Labs 2.0 featuring a new search engine, full-text search functionality, scalable facets and an API was introduced. In 2015 the new ADS, codenamed Bumblebee, was released as ADS-beta. The ADS-beta system features a microservices API and client-side dynamic page loading served on a cloud platform. In May 2018 the beta label was dropped and Bumblebee became the default ADS interface—with some legacy features (ADS Classic) remaining available.<ref>{{Cite conference |last1=Accomazzi |first1=Alberto |last2=Kurtz |first2=Michael J. |last3=Henneken |first3=Edwin |last4=Grant |first4=Carolyn S. |last5=Thompson |first5=Donna M. |last6=Chyla |first6=Roman |last7=McDonald |first7=Steven |last8=Shaulis |first8=Taylor J. |last9=Blanco-Cuaresma |first9=Sergi |last10=Shapurian |first10=Golnaz |last11=Hostetler |first11=Timothy W. |last12=Templeton |first12=Matthew R. |last13=Lockhart |first13=Kelly E. |date=January 2018 |title=ADS Bumblebee comes of age |conference=231st Meeting of the American Astronomical Society |at=362.17 |bibcode=2018AAS...23136217A}}</ref> Development continues to the present day, with an extensible [[API]] available: enabling users to build their own utilities on top of the ADS bibliographic record.
▲The ADS service is distributed worldwide, with twelve [[Web mirror|mirror sites]] in twelve countries on five continents, with the database synchronized by means of weekly updates using [[rsync]], a mirroring utility which allows updates to only the portions of the database which have changed. All updates are triggered centrally, but they initiate scripts at the mirror sites which "pull" updated data from the main ADS servers.<ref name="architecture">{{cite journal |last1=Accomazzi |first1=A. |last2=Eichhorn |first2=G. |last3=Kurtz |first3=M.J. |last4=Grant |first4=C.S. |last5=Murray |first5=S.S. |year=2000 |title=The NASA Astrophysics Data System: Architecture |journal=Astronomy and Astrophysics Supplement Series |volume=143 |issue=1 |pages=85–109 |doi=10.1051/aas:2000172 |bibcode=2000A&AS..143...85A |arxiv=astro-ph/0002105 |s2cid=7182316}}</ref>
==Data in the system==
At first, the journal articles available via ADS were exclusively [[Image scanner|scan]]ned [[bitmap]]s created from the paper journals and the abstracts created using [[optical character recognition]] software. Some of these scanned articles up to around 1995 are available for free by agreement with the journal publishers,<ref name="data">{{cite web |date=23 June 2005 |title=NASA ADS Abstract Service Mirroring Information |url=http://ads.harvard.edu/mirror/ |access-date=2 November 2008 |publisher=Harvard-Smithsonian Center for Astrophysics}}</ref> with some dating from as far back as the early 19th century. Eventually, because of a wider spread of online editions of journal publications, abstracts would start to instead be loaded into ADS directly.
[[Image:M101 hires STScI-PRC2006-10a.jpg|thumb|left|1,284 papers about [[Pinwheel Galaxy|M101]] are available through ADS, from as long ago as 1850.]]
Papers are indexed within the database by their bibliographic record which contains the details of the journal they were published in, and various associated [[metadata]], such as author lists, [[Image resolution|reference]]s and [[citation]]s. Originally this data was stored in [[ASCII]] format, but, eventually, the limitations of this encouraged the database maintainers to migrate all records to an [[XML]] (Extensible Markup Language) format in 2000. Bibliographic records are now stored as an XML element, with sub-elements for the various metadata.<ref name="architecture" /> ▼
▲Papers are indexed within the database by their bibliographic record which contains the details of the journal they were published in, and various associated [[metadata]], such as author lists, [[Image resolution|reference]]s and [[citation]]s. Originally this data was stored in [[ASCII]] format , but , eventually , the limitations of this encouraged the database maintainers to migrate all records to an [[XML]] (Extensible Markup Language) format in 2000. Bibliographic records are now stored as an XML element , with sub-elements for the various metadata.<ref name="architecture" />
Since the advent of online editions of journals, abstracts are loaded into the ADS on or before the publication date of articles, with the full journal text available to subscribers. Older articles have been scanned, and an abstract is created using [[optical character recognition]] software. Scanned articles from before about 1995 are usually available free, by agreement with the journal publishers.<ref name="data">{{cite web |url=http://ads.harvard.edu/mirror/ |date=23 June 2005 |title=NASA ADS Abstract Service Mirroring Information |publisher=Harvard-Smithsonian Center for Astrophysics |access-date=2 November 2008}}</ref>
Scanned articles are stored in [[TIFF]] format, at both medium and high [[Image resolution|resolution]]. The TIFF files are converted on demand into GIF files, for on-screen viewing, and [[PDF]], or [[PostScript]] files for printing. The generated files are then [[cache (computing)|cached]] to eliminate needlessly frequent regenerations for popular articles. As of 2000, ADS contained 250 [[gigabyte|GB]] of scans, which consisted of 1,128,955 article pages comprising 138,789 articles. By 2005 this had grown to 650 GB, and iswas expected to grow further, to about 900 GB by 2007.<ref name="data" /> No further information has been published (2005).
The database initially contained only astronomical references, but has now grown to incorporate three databases, covering [[astronomy]]
references (including planetary sciences and solar physics), [[physics]] references (including instrumentation and geosciences), as well as preprints of scientific papers from [[arXiv]]. The astronomy database is by far the most advanced and its use accounts for about 85% of the total ADS usage. Articles are assigned to the different databases according to the subject rather than the journal they are published in, so that articles from any one journal might appear in all three subject databases. The separation of the databases allows searching in each discipline to be tailored, so that words can automatically be given different [[weight function]]s in different database searches, depending on how common they are in the relevant field.<ref name="architecture"/>
Data in the preprint archive is updated daily from the [[arXiv]], which is the maindominant repository of physics and astronomy preprints. The advent of preprint servers has, like ADS, had a significant impact on the rate of astronomical research, as papers are often made available from preprint servers weeks or months before they are published in the journals. The incorporation of preprints from the arXiv into ADS means that the search engine can return the most current research available, with the caveat that preprints may not have been peer-reviewed or [[proofread]] to the required standard for publication in the main journals. ADS'sThe database of ADS links preprints with subsequently published articles wherever possible, so that citation and reference searches will return links to the journal article where the preprint was cited.<ref>{{cite conference |url=http://meetings.aps.org/Meeting/MAR07/Event/61837 |title=myADS-arXiv: A fully customized, open access virtual journal |conference=March Meeting 2007, American Physical Society |volume=52 |issue=1 |at=U20.9 |access-date=30 October 2008}}</ref>
==Software and hardware==
The software runs on a system that was written specifically for itthe ADS, allowing for extensive customization for astronomical needs that would not have been possible with general purpose [[database]] software. The scripts are designed to be as [[platform independent]] as possible, given the need to facilitate mirroring on different systems around the world, although the growing use of [[Linux]] as the [[operating system]] of choice within astronomy has led to increasing optimization of the scripts for installation on that platform.<ref name="architecture"/>
The main ADS server is located at the [[Harvard-Smithsonian Center for Astrophysics|Center for Astrophysics {{!}} Harvard & Smithsonian]] in [[Cambridge, Massachusetts]], and is a dual 64-bit X86 [[Intel]] server with two quad-core 3.0 [[GHz]] [[Central processing unit|CPU]]s and 32 GB of [[random access memory|RAM]], running the [[CentOS]] 5.4 [[Linux]] distribution.<ref name="data" /> MirrorsAs of 2022, there are mirrors located in Brazil, China, Chile, France, Germany, India, Indonesia, Japan, Russia, South Korea,the United Kingdom, and Ukraine.<ref>{{cite web |url=http://doc.adsabs.harvard.edu/mirrors.html |title=SAO/NASA ADS at SAO: Mirror Sites |publisherurl=Harvard-Smithsonian Center for Astrophysics |access-date=30 October 2008http://doc.adsabs.harvard.edu/mirrors.html |archiveurl=https://web.archive.org/web/2008022708381920220128092136/httphttps://doc.adsabs.harvard.edu/mirrors.html |archive-date=2728 FebruaryJanuary 20082022 |access-date=26 July 2024 |publisher=Harvard-Smithsonian Center for Astrophysics}}</ref>
==Indexing==
==Coverage==
The database now contains over eightfifteen million articles. In the cases of the major journals of astronomy (''[[Astrophysical Journal]]'', ''[[Astronomical Journal]]'', ''[[Astronomy and Astrophysics]]'', ''[[Publications of the Astronomical Society of the Pacific]]'' and the ''[[Monthly Notices of the Royal Astronomical Society]]''), coverage is complete, with all issues indexed from number 1 to the present. These journals account for about two-thirds of the papers in the database, with the rest consisting of papers published in over 100 other journals from around the world, as well as in conference proceedings.<ref name="data" />
While the database contains the complete contents of all the major journals and many minor ones as well, its coverage of references and citations is much less complete. References in and citations of articles in the major journals are fairly complete, but references such as "private communication", "in press" or "in preparation" cannot be matched, and author errors in reference listings also introduce potential errors. Astronomical papers may cite and be cited by articles in journals which fall outside the scope of ADS, such as [[chemistry]], [[mathematics]] or [[biology]] journals.<ref>{{cite web |url=http://adsabs.harvard.edu/abs_doc/journals1.html |title=ADS Bibliographic Codes: Journal Abbreviations |publisher=Harvard-Smithsonian Center for Astrophysics |access-date=30 October 2008 |archiveurl=https://web.archive.org/web/20080430032916/http://adsabs.harvard.edu/abs_doc/journals1.html |archive-date=30 April 2008}}</ref>
===Synonym replacement===
Once search terms have been pre-processedpreprocessed, the database is queried with the revised search term, as well as synonyms for it. As well as simple [[synonym]] replacement such as searching for both [[plural]] and [[Grammatical number|singular]] forms, ADS also searches for a large number of specifically astronomical synonyms. For example, [[spectrograph]] and [[spectroscope]] have basically the same meaning, and in an astronomical context [[metallicity]] and [[Abundance of the chemical elements|abundance]] are also synonymous. ADS's synonym list was created manually, by grouping the list of words in the database according to similar meanings.<ref name="architecture"/>
As well as [[English language]] synonyms, ADS also searches for English translations of foreign search terms and vice versa, so that a search for the [[French language|French]] word ''soleil'' retrieves references to [[Sun]], and papers in languages other than English can be returned by English search terms.
===Result filtering===
Search results can be filtered according to a number of criteria, including specifying a range of years such as '"1945 to 1975'", '"2000 to the present day'" or '"before 1900'", and what type of journal the article appears in [–] non-peer-reviewed articles such as [[academic conference|conference]] proceedings. These can be excluded or specifically searched for, or specific journals can be included in or excluded from the search.
==Search results==
[[Image:ADS search results.png|thumb|right|Search results page from ADS – A, F, G, C, R etc. are links to associated data for each abstract such as full-text article, citations, also-read papers and so on.]]
Although it was conceived as a means of accessing abstracts and papers, ADS provides a substantial amount of ancillary information along with search results. For each abstract returned, links are provided to other papers in the database which are referenced, and which cite the paper, and a link is provided to a preprint, where one exists. The system also generates a link to '"also-read'" articles – that is, those which have been most commonly accessed by those reading the article. In this way, an ADS user can determine which papers are of most interest to astronomers who are interested in the subject of a given paper.<ref name="search" />
Also returned are links to the [[SIMBAD]] and/or [[NASA Extragalactic Database]] object name databases, via which a user can quickly find out basic observational data about the objects analyzed in a paper, and find further papers on those objects.
==Impact on astronomy==
ADS is almost universally used as a research tool among astronomers, and there are several studies that have estimated quantitatively how much more efficient ADS has made astronomy; one estimated that ADS increased the efficiency of astronomical research by 333 full-time equivalent research years per year,<ref name="overview" /> and another found that in 2002 its effect was equivalent to 736 full-time researchers, or all the astronomical research done in France.<ref name="impact">{{cite journal |last=Kurtz |first=M.J. |author2=Eichhorn G. |author3=Accomazzi A. |author4=Grant C.S. |author5=Demleitner M. |author6=Murray S.S. |year=2005 |title=Worldwide Use and Impact of the NASA Astrophysics Data System Digital Library |journal=Journal of the American Society for Information Science and Technology |volume=56 |issue=1 |pages=36–45 |arxiv=0909.4786 |bibcode=2005JASIS..56...36K |doi=10.1002/asi.20095 |s2cid=15181632}} ([http://cfa-www.harvard.edu/~kurtz/jasis-abstract.html Preprint])</ref> ADS has allowed literature searches that would previously have taken days or weeks to carry out to be completed in seconds, and it is estimated that ADS has increased the readership and use of the astronomical literature by a factor of about three since its inception.<ref name="impact" />
In monetary terms, this increase in efficiency represents a considerable amount. There are about 12,000 active astronomical researchers worldwide, so ADS is the equivalent of about 5% of the working population of astronomers. The global astronomical research budget is estimated at between 4,000 and US$5,000 million,<ref name="woltjer">{{cite conference |last=Woltjer |first=L. |year=1998 |title=Economic Consequences of the Deterioration of the Astronomical Environment |conference=23rd General Assembly of the International Astronomical Union |book-title=Preserving The Astronomical Windows. Proceedings of Joint Discussion number 5 of the 23rd General Assembly of the International Astronomical Union held in Kyoto, Japan 22–23 August 1997 |volume=139 |pages=243 |bibcode=1998ASPC..139..243W}}</ref> so the value of ADS to astronomy would be about 200–250 million USD annually. Its operating budget is a small fraction of this amount.<ref name="impact" />
The great importance of ADS to astronomers has been recognized by the [[United Nations]], the [[United Nations General Assembly|General Assembly]] of which has commended ADS on its work and success, particularly noting its importance to astronomers in the developing world, in reports of the [[United Nations Committee on the Peaceful Uses of Outer Space]]. A 2002 report by a visiting committee to the Center for Astrophysics, meanwhile, said that the service had "revolutionized the use of the astronomical literature", and was "probably the most valuable single contribution to astronomy research that the CfA has made in its lifetime".<ref name="awards">{{cite web |url=https://ui.adsabs.harvard.edu/about/awards.html |title=ADS Awards and Recognition |publisher=Harvard-Smithsonian Center for Astrophysics |access-date=25 March 2022}}</ref>
* [[Bibcode]]
* [[INSPIRE-HEP]]
* [[NASA]]'s [[Planetary Data System]] (PDS)
* [[PubMed]]
* [[Michael J. Kurtz]]
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