3 Description of the data

The original set of data from STI contained several basic fields of data (author, title, keywords, and abstracts) to be indexed and made available for searching. All records were keyed on STI's accession number, a nine-digit code consisting of a letter prefix (A or N) followed by a two-digit publication year, followed by a five-letter identifier (e.g. A95-12345). Data were stored in files named by accession number.

With the inclusion of data from other sources, primarily the journal publishers and SIMBAD, we extended STI's concept of the accession number to handle other abstracts as well. Since the ADS may receive the same abstract from multiple sources, we originally adopted a system of using a different prefix letter with the remainder of the accession number being the same to describe abstracts received from different sources. Thus, the same abstract for the above accession number from STI would be listed as J95-12345 from the journal publisher and S95-12345 from SIMBAD. This allowed the indexing routines to consider only one instance of the record when indexing. Recently, limitations in the format of accession numbers and the desire to index data from multiple sources (rather than just STI's version) have prompted us to move to a data storage system based entirely on the bibliographic code.

3.1 Bibliographic codes

The concept of a unique bibliographic code used to identify an article was originally conceived of by SIMBAD and NED (NASA's Extragalactic Database, [Helou & Madore 1988]). The original specification is detailed in [Schmitz et al. (1995)]. In the years since, the ADS has adopted and expanded their definition to be able to describe references outside of the scope of those projects.

The bibliographic code is a 19-character string comprised of several fields which usually enables a user to identify the full reference from that string. It is defined as follows:

The journal field is left-justified and the volume and page fields are right-justified. Blank spaces and leading zeroes are replaced by periods. For articles with page numbers greater than 9999, the M field contains the first digit of the page number.

Creating bibliographic codes for the astronomical journals is uncontroversial. Each journal typically has a commonly-used abbreviation, and the volume and page are easily assigned (e.g. 1999PASP..111..438F). Each volume tends to have individual page numbering, and in those cases where more than one article appears on a page (such as errata), a "Q","R","S", etc. is used as the qualifier for publication to make bibliographic codes unique. When page numbering is not continuous across issue numbers (such as Sky & Telescope), the issue number is represented by a lower case letter as the qualifier for publication (e.g. "a" for issue 1). This is because there may be multiple articles in a volume starting on the same page number.

Creating bibliographic codes for the "grey" literature such as conference proceedings and technical reports is a more difficult task. The expansion into these additional types of data included in the ADS required us to modify the original prototype bibliographic code definition in order to present identifiers which are easily recognizable to the user. The prototype definition of the bibliographic code suggested using a single letter in the second place of the volume field to identify non-standard references (catalogs, PhD theses, reports, preprints, etc.) and using the third and fourth place of that field to unduplicate and report volume numbers (e.g. 1981CRJS..R.3...14W). Since we felt that this created codes unidentifiable to the typical user and since NED and SIMBAD did not feel that users needed to be able to identify books directly from their bibliographic codes, the ADS adopted different rules for creating codes to identify the grey literature.

**Table 1:** Bibliographic code definition (e.g. 1996A&AS..115....1S)
Field	Definition	Example
YYYY	Publication Year	1997
JJJJJ	Journal Abbreviation	ApJ, A&A, MNRAS, etc.
VVVV	Volume Number	480
M	Qualifier for Publication	L (for Letter), P (for Pink Page)
		Q, R, S, etc. for unduplicating
		a, b, c, etc. for issue number
PPPP	Page Number	129
A	First Letter of the First Author's Surname	N

It is straightforward to create bibliographic codes for conference proceedings which are part of a series. For example, the IAU Symposia Series (IAUS) contains volume numbers and therefore fits the journal model for bibliographic codes. Other conference proceedings, books, colloquia, and reports in the ADS typically contain a four letter word in the volume field such as "conf", "proc", "book", "coll", or "rept". When this is the case with a bibliographic code, the journal field typically consists of the first letter from important words in the title. This can give the user the ability to identify a conference proceeding at a glance (e.g. "ioda.book" for "Information and On-Line Data in Astronomy"). We will often leave the fifth place of the journal field as a dot for "readability" (e.g. 1995ioda.book..175M). For most proceedings which are also published as part of a series (e.g. ASP Conference Series, IAU Colloquia, AIP Conference Series), we include in the system two bibliographic codes, one as described above and one which contains the series name and the volume (see Sect. 5.1). We do this so that users can see, for example, that a paper published in one of the "Astronomical Data Analysis Software and Systems" series is clearly labelled as "adass" whereas a typical user might not remember which volume of ASPC contained those ADASS papers. This increases the user's readability of bibliographic codes.

With the STI data, the details were often unclear as to whether an article was from a conference proceeding, a meeting, a colloquium, etc. We assigned those codes as best we could, making no significant distinction between them. For conference abstracts submitted by the editors of a proceedings prior to publication, we often do not have page numbers. In this case, we use a counter in lieu of a page number and use an "E" (for "Electronic") in the fourteenth column, the qualifier for publication. If these conference abstracts are then published, their bibliographic codes are replaced by a bibliographic code complete with page number. If the conference abstracts are published only on-line, they retain their electronic bibliographic code with its E and counter number.

There are several other instances of datasets where the bibliographic codes are non-standard. PhD theses in the system use "PhDT" as the journal abbreviation, contain no volume number, and contain a counter in lieu of a page number. Since PhD theses, like all bibliographic codes, are unique across all of the databases, the counter makes the bibliographic code an identifier for only one thesis. IAU Circulars also use a counter instead of a page number. Current Circulars are electronic in form, and although not technically a new page, the second item of an IAU Circular is the electronic equivalent of a second page. Using the page number as a counter enables us to minimize use of the M identifier in the fourteenth place of a bibliographic code for unduplicating. This is desirable since codes containing those identifiers are essentially impossible to create a priori, either by the journals or by users.

The last set of data currently included in the ADS which contain non-standard bibliographic codes is the "QB" book entries from the Library of Congress. QB is the Library of Congress code for astronomy-related books and we have put approximately 17 000 of these references in the system. Because the QB numbers are identifiers by themselves, we have made an exception to the bibliographic code format to use the QB number (complete with any series or part numbers), prepended with the publication year as the bibliographic code. Such an entry is easily identifiable as a book, and these codes enable users to locate the books in most libraries.

It is worth noting that while the bibliographic code makes identification simple for the vast majority of references in the system, we are aware of two instances where the bibliographic definition breaks down. The use of the fourteenth column for a qualifier such as "L" for ApJ Letters makes it impossible to use that column for unduplicating. Therefore, if there are two errata on the same page with the same author initial, there is no way to create unique bibliographic codes for them. We are aware of only one such instance in the 33 years of publication of ApJ Letters. Second, with the electronic publishing of an increasing number of journals, the requirement of page numbers to locate articles becomes unnecessary. The journal Physical Review D is currently using 6-digit article identifiers as page numbers. Since the bibliographic code allows for page numbers not longer than 5 digits, we are currently converting these 6-digit identifiers to their 5-digit hexagesimal equivalent. Both of these anomalies indicate that over the next few years we will likely need to alter the current bibliographic definition in order to allow consistent identification of articles for all journals.

3.2 Data fields

The databases are set up such that some data fields are searchable and others are not. The searchable fields (title, author, and text) are the bulk of the important data, and these fields are indexed so that a query to the database returns the maximum number of meaningful results. (see [Accomazzi et al. 2000], hereafter ARCHITECTURE). The text field is the union of the abstract, title, keywords, and comments. Thus, if a user requests a particular word in the text field, all papers are returned which contain that word in the abstract OR in the title OR in the keywords OR in the comments. Appendix A shows version 1.0 of the Extensible Markup Language (XML, see Sect. 3.4) Document Type Definition (DTD) for text files in the ADS Abstract Service. The DTD lists fields currently used or expected to be used in text files in the ADS (see Sect. 5.2 for details on the text files). We intend to reprocess the current journal and affiliation fields in order to extract some of these fields. Since STI ceased abstracting the journal literature, we decided to make the keywords themselves no longer a searchable entity for the time being - they are searchable only through the abstract text field. STI used a different standard set of keywords from the AAS journals, who use a different set of keywords from AIP journals (e.g. AJ prior to 1998). In addition, keywords from a single journal such as the Astrophysical Journal (ApJ) have evolved over the years so that early ApJ volume keywords are not consistent with later volumes. In order to build one coherent set of keywords, an equivalence or synonym table for these different keyword sets must be created. We are investigating different schemes for doing this, and currently plan to have a searchable keyword field again, which encompasses all keywords in the system and equates those from different keyword systems which are similar ([Lee et al. 1999]).

The current non-searchable fields in the ADS databases include the journal field, author affiliation, category, abstract copyright, and abstract origin. Although we may decide to create an index and search interface for some of these entities (such as category), others will continue to remain unsearchable since searching them is not useful to the typical user. In particular, author affiliations would be useful to search, however this information is inconsistently formatted so it is virtually impossible to collect all variations of a given institution for indexing coherently. Furthermore, we have the author affiliations for only about half of the entries in the Astronomy database so we have decided to keep this field non-searchable. For researchers wishing to analyze affiliations on a large scale, we can provide this information on a collaborative basis.

3.3 Data sources

The ADS currently receives abstracts or table of contents (ToC) references from almost two hundred journal sources. Tables 2, 3, and 4 list these journals, along with their bibliographic code abbreviation, source, frequency with which we receive the data, what data are received, and any links we can create to the data. ToC references typically contain only author and title, although sometimes keywords are included as well. The data are contributed via email, ftp, or retrieved from web sites around the world at a frequency ranging from once a week to approximately once a year. The term "often" used in the frequency column implies that we get them more frequently than once a month, but not necessarily on a regular basis. The term "occasionally" is used for those journals who submit data to us infrequently.

Table 2: The ADS astronomy database
Journal Source Full Name How Often Kind of Data Links ^a

A&A Springer Astronomy & Astrophysics 3 $\times$ month abstracts E, F

A&ARv Springer Astronomy & Astrophysics Review occasionally abstracts F

A&AS EDP Sciences Astronomy & Astrophysics Supplement 2 $\times$ month abstracts E, F, R

AcA AcA Acta Astronomica 4 $\times$ year abstracts G

ADIL NCSA ADIL Astronomy Data Image Library occasionally abstracts D

AdSpR Elsevier Advances in Space Research often abstracts

AGAb AG ^b Astronomische Gesellschaft Abstracts occasionally abstracts

AJ UCP ^c Astronomical Journal monthly abstracts E, F, R

AN AN Astronomische Nachrichten bimonthly abstracts

Ap&SS Kluwer Astrophysics and Space Science often abstracts

APh Elsevier Astroparticle Physics bimonthly abstracts E

ApJ UCP Astrophysical Journal 3 $\times$ month abstracts E, F, R

ApJL UCP Astrophysical Journal Letters 3 $\times$ month abstracts E, F, R

ApJS UCP Astrophysical Journal Supplement monthly abstracts E, F, R

ARA&A AnnRev Annual Review of Astronomy and Astrophysics 1 $\times$ year abstracts E, F

AREPS AnnRev Annual Review of Earth and Planetary Sciences 1 $\times$ year abstracts E, F

ARep AIP ^d Astronomy Reports bimonthly abstracts M

AstL AstL Astronomy Letters bimonthly abstracts M

ATel ATel The Astronomer's Telegram often abstracts E

AVest AVest Astronomicheskii Vestnik bimonthly abstracts

BAAS AAS Bulletin of the American Astronomical Society 2 $\times$ year (AAS) abstracts

BAAS AAS Bulletin of the American Astronomical Society 1 $\times$ year (DDA) abstracts

BAAS AAS Bulletin of the American Astronomical Society 1 $\times$ year (DPS) abstracts

BAAS AAS Bulletin of the American Astronomical Society 1 $\times$ year (HEA) abstracts

BAAS AAS Bulletin of the American Astronomical Society 1 $\times$ year (SPD) abstracts

BaltA BaltA Baltic Astronomy 4 $\times$ year abstracts R

BeSN BeSN BE Star Newsletter occasionally ToC G

BOBeo BOBeo Bulletin Astronomique de Belgrade occasionally abstracts G

Books CUP Cambridge University Press occasionally ToC

Books LOC Library of Congress occasionally abstracts L

Books Springer Springer Verlag occasionally ToC

Books USci University Science Books Publishers occasionally abstracts M

Books Wiley Wiley Publishers occasionally abstracts

CeMDA Kluwer Celestial Mechanics and Dynamical Astronomy often abstracts

ChA&A Elsevier Chinese Astronomy and Astrophysics 4 $\times$ year ToC

CoKon Konkoly Communications of the Konkoly Observatory occasionally abstracts G

Conferences Boon Priscilla Boon, Conference Proceedings occasionally ToC

Conferences Editors Conference Proceeding Editor Submissions often abstracts

Conferences ESO European Southern Observatory Library monthly ToC

Conferences LPI Lunar and Planetary Institute Proceedings occasionally abstracts F

Conferences STSci Space Telescope Science Institute Library monthly ToC

Conferences UTAL University of Toronto Library weekly ToC

CoSka CoSka Contributions from the Ast. Obs. Skalnate Pleso occasionally abstracts G

DSSN DSSN Delta Scuti Star Newsletter occasionally abstracts E

DyAtO Elsevier Dynamics of Atmospheres and Oceans occasionally ToC

E&PSL Elsevier Earth & Planetary Science Letters occasionally ToC E, D

EM&P Kluwer Earth, Moon, and Planets often abstracts

ESRv Elsevier Earth Science Reviews occasionally ToC

ExA Kluwer Experimental Astronomy occasionally abstracts

FCPh OPA ^e Fundamentals of Cosmic Physics occasionally abstracts

GeCoA Elsevier Geochimica et Cosmochimica Acta often ToC

GeoRL AGU ^f Geophysical Research Letters 2 $\times$ month ToC E, F

GeoJI Blackwell Geophysical Journal International 2 $\times$ month abstracts E, F, R

GReGr Plenum General Relativity and Gravitation monthly abstracts

IAUC CBAT ^g IAU Circulars weekly abstracts E

IBVS Konkoly Information Bulletin on Variable Stars often abstracts E, F

Icar AP ^h Icarus monthly abstracts E, F, R

**Table 2:** The ADS astronomy database
Journal	Source	Full Name	How Often	Kind of Data	Links ^a
A&A	Springer	Astronomy & Astrophysics	3 $\times$ month	abstracts	E, F
A&ARv	Springer	Astronomy & Astrophysics Review	occasionally	abstracts	F
A&AS	EDP Sciences	Astronomy & Astrophysics Supplement	2 $\times$ month	abstracts	E, F, R
AcA	AcA	Acta Astronomica	4 $\times$ year	abstracts	G
ADIL	NCSA ADIL	Astronomy Data Image Library	occasionally	abstracts	D
AdSpR	Elsevier	Advances in Space Research	often	abstracts
AGAb	AG ^b	Astronomische Gesellschaft Abstracts	occasionally	abstracts
AJ	UCP ^c	Astronomical Journal	monthly	abstracts	E, F, R
AN	AN	Astronomische Nachrichten	bimonthly	abstracts
Ap&SS	Kluwer	Astrophysics and Space Science	often	abstracts
APh	Elsevier	Astroparticle Physics	bimonthly	abstracts	E
ApJ	UCP	Astrophysical Journal	3 $\times$ month	abstracts	E, F, R
ApJL	UCP	Astrophysical Journal Letters	3 $\times$ month	abstracts	E, F, R
ApJS	UCP	Astrophysical Journal Supplement	monthly	abstracts	E, F, R
ARA&A	AnnRev	Annual Review of Astronomy and Astrophysics	1 $\times$ year	abstracts	E, F
AREPS	AnnRev	Annual Review of Earth and Planetary Sciences	1 $\times$ year	abstracts	E, F
ARep	AIP ^d	Astronomy Reports	bimonthly	abstracts	M
AstL	AstL	Astronomy Letters	bimonthly	abstracts	M
ATel	ATel	The Astronomer's Telegram	often	abstracts	E
AVest	AVest	Astronomicheskii Vestnik	bimonthly	abstracts
BAAS	AAS	Bulletin of the American Astronomical Society	2 $\times$ year (AAS)	abstracts
BAAS	AAS	Bulletin of the American Astronomical Society	1 $\times$ year (DDA)	abstracts
BAAS	AAS	Bulletin of the American Astronomical Society	1 $\times$ year (DPS)	abstracts
BAAS	AAS	Bulletin of the American Astronomical Society	1 $\times$ year (HEA)	abstracts
BAAS	AAS	Bulletin of the American Astronomical Society	1 $\times$ year (SPD)	abstracts
BaltA	BaltA	Baltic Astronomy	4 $\times$ year	abstracts	R
BeSN	BeSN	BE Star Newsletter	occasionally	ToC	G
BOBeo	BOBeo	Bulletin Astronomique de Belgrade	occasionally	abstracts	G
Books	CUP	Cambridge University Press	occasionally	ToC
Books	LOC	Library of Congress	occasionally	abstracts	L
Books	Springer	Springer Verlag	occasionally	ToC
Books	USci	University Science Books Publishers	occasionally	abstracts	M
Books	Wiley	Wiley Publishers	occasionally	abstracts
CeMDA	Kluwer	Celestial Mechanics and Dynamical Astronomy	often	abstracts
ChA&A	Elsevier	Chinese Astronomy and Astrophysics	4 $\times$ year	ToC
CoKon	Konkoly	Communications of the Konkoly Observatory	occasionally	abstracts	G
Conferences	Boon	Priscilla Boon, Conference Proceedings	occasionally	ToC
Conferences	Editors	Conference Proceeding Editor Submissions	often	abstracts
Conferences	ESO	European Southern Observatory Library	monthly	ToC
Conferences	LPI	Lunar and Planetary Institute Proceedings	occasionally	abstracts	F
Conferences	STSci	Space Telescope Science Institute Library	monthly	ToC
Conferences	UTAL	University of Toronto Library	weekly	ToC
CoSka	CoSka	Contributions from the Ast. Obs. Skalnate Pleso	occasionally	abstracts	G
DSSN	DSSN	Delta Scuti Star Newsletter	occasionally	abstracts	E
DyAtO	Elsevier	Dynamics of Atmospheres and Oceans	occasionally	ToC
E&PSL	Elsevier	Earth & Planetary Science Letters	occasionally	ToC	E, D
EM&P	Kluwer	Earth, Moon, and Planets	often	abstracts
ESRv	Elsevier	Earth Science Reviews	occasionally	ToC
ExA	Kluwer	Experimental Astronomy	occasionally	abstracts
FCPh	OPA ^e	Fundamentals of Cosmic Physics	occasionally	abstracts
GeCoA	Elsevier	Geochimica et Cosmochimica Acta	often	ToC
GeoRL	AGU ^f	Geophysical Research Letters	2 $\times$ month	ToC	E, F
GeoJI	Blackwell	Geophysical Journal International	2 $\times$ month	abstracts	E, F, R
GReGr	Plenum	General Relativity and Gravitation	monthly	abstracts
IAUC	CBAT ^g	IAU Circulars	weekly	abstracts	E
IBVS	Konkoly	Information Bulletin on Variable Stars	often	abstracts	E, F
Icar	AP ^h	Icarus	monthly	abstracts	E, F, R

Table 2: continued
Journal Source Full Name How Often Kind of Data Links ^a

IrAJ IrAJ Irish Astronomical Journal 2 $\times$ year abstracts

JASS JASS Journal of Astronomy and Space Sciences occasionally abstracts F

JAVSO AAVSO Journal of the A.A.V.S.O. occasionally abstracts

JBAA BAA Journal of the British Astronomical Association bimonthly abstracts

JIMO IMO Journal of the International Meteor Organization occasionally abstracts

JGR AGU Journal of Geophysical Research A (Space Physics) monthly ToC

JGR AGU Journal of Geophysical Research E (Planets) monthly ToC

JKAS KAS Journal of the Korean Astronomical Society occasionally abstracts

JRASC RASC Journal of the Royal Astronomical Society of Canada occasionally abstracts

M&PS M&PS Meteoritics & Planetary Science bimonthly abstracts

MNRAS Blackwell Monthly Notices of the Royal Astronomical Society 3 $\times$ month abstracts E, F, R

MPEC CBAT Minor Planet Electronic Circulars weekly abstracts E

Nature Nature Nature weekly abstracts

NewA Elsevier New Astronomy often abstracts E

NewAR Elsevier New Astronomy Reviews (formerly VA) occasionally abstracts

OAP OAP Odessa Astronomical Publications occasionally abstracts

Obs Obs The Observatory occasionally ToC

P&SS Elsevier Planetary and Space Science monthly ToC

PASA PASA Publications of the Astronomical Society of Australia 2 $\times$ year abstracts E, F

PASJ PASJ Publications of the Astronomical Society of Japan bimonthly abstracts R

PASP UCP Publications of the Astronomical Society of the Pacific monthly abstracts E, F, R

PDS PDS Planetary Data System occasionally abstracts P

PEPI Elsevier Physics of the Earth and Planetary Interiors monthly ToC

PhDT UMass University of Massachusetts occasionally abstracts D

PhDT UMI University Microfilm, Inc. occasionally abstracts M

PKAS KAS Publications of the Korean Astronomical Society occasionally abstracts

RvMA AG Reviews of Modern Astronomy occasionally ToC

RMxAC UNAM ⁱ Revista Mexicana Conference Series occasionally ToC

S&T Sky Publishing Sky & Telescope 2 $\times$ year ToC

Sci Science Science weekly ToC E

SoPh Stet. Solar Physics often abstracts

SSRv Kluwer Space Science Reviews often abstracts

VA Elsevier Vistas in Astronomy occasionally ToC

Various ARI ^j Veröffentlichungen ARI occasionally ToC L

Various Authors Author Submissions often abstracts

Various Knudsen Helen Knudsen's Monthly Index of Astronomy occasionally ToC

Various NED NASA Extragalactic Database occasionally ToC N

Various SIMBAD SIMBAD 2 $\times$ month ToC D, S

Various STI NASA's Science and Technical Index 2 $\times$ month abstracts

Various USNO United States Naval Observatory Library occasionally ToC

**Table 2:** continued
Journal	Source	Full Name	How Often	Kind of Data	Links ^a
IrAJ	IrAJ	Irish Astronomical Journal	2 $\times$ year	abstracts
JASS	JASS	Journal of Astronomy and Space Sciences	occasionally	abstracts	F
JAVSO	AAVSO	Journal of the A.A.V.S.O.	occasionally	abstracts
JBAA	BAA	Journal of the British Astronomical Association	bimonthly	abstracts
JIMO	IMO	Journal of the International Meteor Organization	occasionally	abstracts
JGR	AGU	Journal of Geophysical Research A (Space Physics)	monthly	ToC
JGR	AGU	Journal of Geophysical Research E (Planets)	monthly	ToC
JKAS	KAS	Journal of the Korean Astronomical Society	occasionally	abstracts
JRASC	RASC	Journal of the Royal Astronomical Society of Canada	occasionally	abstracts
M&PS	M&PS	Meteoritics & Planetary Science	bimonthly	abstracts
MNRAS	Blackwell	Monthly Notices of the Royal Astronomical Society	3 $\times$ month	abstracts	E, F, R
MPEC	CBAT	Minor Planet Electronic Circulars	weekly	abstracts	E
Nature	Nature	Nature	weekly	abstracts
NewA	Elsevier	New Astronomy	often	abstracts	E
NewAR	Elsevier	New Astronomy Reviews (formerly VA)	occasionally	abstracts
OAP	OAP	Odessa Astronomical Publications	occasionally	abstracts
Obs	Obs	The Observatory	occasionally	ToC
P&SS	Elsevier	Planetary and Space Science	monthly	ToC
PASA	PASA	Publications of the Astronomical Society of Australia	2 $\times$ year	abstracts	E, F
PASJ	PASJ	Publications of the Astronomical Society of Japan	bimonthly	abstracts	R
PASP	UCP	Publications of the Astronomical Society of the Pacific	monthly	abstracts	E, F, R
PDS	PDS	Planetary Data System	occasionally	abstracts	P
PEPI	Elsevier	Physics of the Earth and Planetary Interiors	monthly	ToC
PhDT	UMass	University of Massachusetts	occasionally	abstracts	D
PhDT	UMI	University Microfilm, Inc.	occasionally	abstracts	M
PKAS	KAS	Publications of the Korean Astronomical Society	occasionally	abstracts
RvMA	AG	Reviews of Modern Astronomy	occasionally	ToC
RMxAC	UNAM ⁱ	Revista Mexicana Conference Series	occasionally	ToC
S&T	Sky Publishing	Sky & Telescope	2 $\times$ year	ToC
Sci	Science	Science	weekly	ToC	E
SoPh	Stet.	Solar Physics	often	abstracts
SSRv	Kluwer	Space Science Reviews	often	abstracts
VA	Elsevier	Vistas in Astronomy	occasionally	ToC
Various	ARI ^j	Veröffentlichungen ARI	occasionally	ToC	L
Various	Authors	Author Submissions	often	abstracts
Various	Knudsen	Helen Knudsen's Monthly Index of Astronomy	occasionally	ToC
Various	NED	NASA Extragalactic Database	occasionally	ToC	N
Various	SIMBAD	SIMBAD	2 $\times$ month	ToC	D, S
Various	STI	NASA's Science and Technical Index	2 $\times$ month	abstracts
Various	USNO	United States Naval Observatory Library	occasionally	ToC

$\textstyle \parbox{12cm}{ $^{\mathrm{a}}$\space Letter codes describing what da... ...l Autonoma de Mexico.\\ $^{\mathrm{j}}$\space Astronomisches Rechen-Institut.}$

Table 3: The ADS instrumentation database
Journal Source Full Name How Often Kind of Data Links ^a

ACAau Elsevier Acta Astronautica often ToC

ApOpt OSA ^b Applied Optics often abstracts M

ApScR Kluwer Applied Scientific Research occasionally ToC

ChJLB OSA Chinese Journal of Lasers B occasionally abstracts

IJQE OSA Journal of Quantum Electronics often abstracts

JBO SPIE ^c Journal of Biomedical Optics occasionally abstracts

JEI SPIE Journal of Electronic Imaging occasionally abstracts

JEnMa Kluwer Journal of Engineering Mathematics occasionally ToC

JMiMi IOP ^d Journal of Micromechanics & Microengineering often ToC E

JO IOP Journal of Optics often ToC E

JOptT OSA Journal of Optical Technology often abstracts M

JVST AIP Journal of Vacuum & Science Technology often ToC M

OptCo Elsevier Optics Communications often abstracts

OptEn SPIE Optical Engineering often abstracts

OptFT AP Optical Fiber Technology often abstracts

OptL OSA Optics Letters often ToC M

OptLE Elsevier Optics and Lasers in Engineering bimonthly ToC

OptLT Elsevier Optics & Laser Technology occasionally ToC

OptPN AIP Optics & Photonics News often abstracts M

OptSp OSA Optics and Spectroscopy often abstracts M

OSAJ AIP Journal of the Optical Society of America A often abstracts M

OSAJB AIP Journal of the Optical Society of America B often abstracts M

PApO IOP Pure Applied Optics often ToC E

PrAeS Elsevier Progress in Aerospace Sciences occasionally ToC

RScI AIP Review of Scientific Instruments often ToC M

SPIE SPIE SPIE Proceedings often abstracts M

**Table 3:** The ADS instrumentation database
Journal	Source	Full Name	How Often	Kind of Data	Links ^a
ACAau	Elsevier	Acta Astronautica	often	ToC
ApOpt	OSA ^b	Applied Optics	often	abstracts	M
ApScR	Kluwer	Applied Scientific Research	occasionally	ToC
ChJLB	OSA	Chinese Journal of Lasers B	occasionally	abstracts
IJQE	OSA	Journal of Quantum Electronics	often	abstracts
JBO	SPIE ^c	Journal of Biomedical Optics	occasionally	abstracts
JEI	SPIE	Journal of Electronic Imaging	occasionally	abstracts
JEnMa	Kluwer	Journal of Engineering Mathematics	occasionally	ToC
JMiMi	IOP ^d	Journal of Micromechanics & Microengineering	often	ToC	E
JO	IOP	Journal of Optics	often	ToC	E
JOptT	OSA	Journal of Optical Technology	often	abstracts	M
JVST	AIP	Journal of Vacuum & Science Technology	often	ToC	M
OptCo	Elsevier	Optics Communications	often	abstracts
OptEn	SPIE	Optical Engineering	often	abstracts
OptFT	AP	Optical Fiber Technology	often	abstracts
OptL	OSA	Optics Letters	often	ToC	M
OptLE	Elsevier	Optics and Lasers in Engineering	bimonthly	ToC
OptLT	Elsevier	Optics & Laser Technology	occasionally	ToC
OptPN	AIP	Optics & Photonics News	often	abstracts	M
OptSp	OSA	Optics and Spectroscopy	often	abstracts	M
OSAJ	AIP	Journal of the Optical Society of America A	often	abstracts	M
OSAJB	AIP	Journal of the Optical Society of America B	often	abstracts	M
PApO	IOP	Pure Applied Optics	often	ToC	E
PrAeS	Elsevier	Progress in Aerospace Sciences	occasionally	ToC
RScI	AIP	Review of Scientific Instruments	often	ToC	M
SPIE	SPIE	SPIE Proceedings	often	abstracts	M

$\textstyle \parbox{12cm}{ $^{\mathrm{a}}$\space Letter codes describing what da... ...for Optical Engineering (SPIE).\\ $^{\mathrm{d}}$\space Institute of Physics.}$

Table 4: The ADS physics database
Journal Source Full Name How Often Kind of Data Links ^a

AcPhy AIP Acoustical Physics occasionally ToC M

ADNDT AP Atomic Data and Nuclear Data Tables occasionally abstracts

AnPhy AP Annals of Physics often abstracts

ApPhL AIP Applied Physics Letters often ToC M

ASAJ AIP Journal of the Acoustical Society of America often ToC M

Chaos AIP Chaos occasionally ToC M

ComPh AIP Computers In Physics occasionally ToC M

CQGra IOP Classical Quantum Gravity often ToC

Cryo Elsevier Cryogenics occasionally ToC

CryRp AIP Crystallography Reports occasionally ToC M

CTM IOP Combustion Theory Modelling often ToC

DokPh AIP Physics - Doklady occasionally ToC

EJPh IOP European Journal of Physics often ToC

InfPh Elsevier Infrared Physics and Technology often abstracts

JAP AIP Journal of Applied Physics often ToC M

JATP Elsevier Journal Atmospheric and Terrestrial Physics occasionally ToC

JChPh AIP Journal of Chemical Physics often ToC M

JCoPh AP Journal of Computational Physics occasionally abstracts

JETP AIP JETP occasionally ToC M

JETPL AIP JETP Letters occasionally ToC M

JFS AP Journal of Fluids and Structures occasionally ToC

JGP Elsevier Journal of Geometry and Physics occasionally ToC

JLTP OSA Journal of Low Temperature Physics occasionally ToC M

JLwT OSA Journal of Lightwave Technology occasionally ToC

JMagR AP Journal of Magnetic Resonance occasionally abstracts

JMMM Elsevier Journal of Magnetism and Magnetic Materials occasionally abstracts

JMPS AIP Journal of Mathematical Physics often ToC M

JMoSp AP Journal of Molecular Spectroscopy occasionally abstracts

JNM Elsevier Journal of Nuclear Materials occasionally ToC

JPCM IOP Journal of the Physics of Condensed Matter often ToC

JPCRD AIP Journal of Physical and Chemical Reference Data occasionally ToC M

JPCS Elsevier Journal of Physics and Chemistry of Solids occasionally ToC

JPhA IOP Journal of Physics A: Mathematical General often ToC

JPhB IOP Journal of Physics B: Atomic Molecular Physics often ToC

JPhD IOP Journal of Physics D: Applied Physics often ToC

JPhG IOP Journal of Physics G: Nuclear Physics often ToC

JRheo AIP Journal of Rheology often ToC M

JSSCh AP Journal of Solid State Chemistry occasionally abstracts

JSV AP Journal of Sound and Vibration often ToC

JTePh AIP Journal of Technical Physics occasionally ToC M

MedPh AIP Medical Physics often ToC M

MSMSE IOP Modelling Simul. Mater. Sci. Eng. often ToC

MSSP AP Mechanical Systems & Signal Processing occasionally abstracts

NIMPA Elsevier Nuclear Instruments/Methods Physics Research A often abstracts

NIMPB Elsevier Nuclear Instruments/Methods Physics Research B often abstracts

Nanot IOP Nanotechnology often ToC

NDS AP Nuclear Data Sheets occasionally abstracts

Nonli IOP Nonlinearity often ToC

NuGeo Elsevier Nuclear Geophysics occasionally ToC

NuPhA Elsevier Nuclear Physics A weekly abstracts E

NuPhB Elsevier Nuclear Physics B weekly abstracts E

NuPhS Elsevier Nuclear Physics B Proceedings Supplements monthly abstracts E

PAN AIP Physics of Atomic Nuclei occasionally ToC M

PCEB Elsevier Physics and Chemistry of the Earth Part B occasionally ToC

PCEC Elsevier Physics and Chemistry of the Earth Part C occasionally ToC

PhFl AIP Physics of Fluids often ToC M

PhLA Elsevier Physics Letters A often abstracts

PhLB Elsevier Physics Letters B often abstracts

**Table 4:** The ADS physics database
Journal	Source	Full Name	How Often	Kind of Data	Links ^a
AcPhy	AIP	Acoustical Physics	occasionally	ToC	M
ADNDT	AP	Atomic Data and Nuclear Data Tables	occasionally	abstracts
AnPhy	AP	Annals of Physics	often	abstracts
ApPhL	AIP	Applied Physics Letters	often	ToC	M
ASAJ	AIP	Journal of the Acoustical Society of America	often	ToC	M
Chaos	AIP	Chaos	occasionally	ToC	M
ComPh	AIP	Computers In Physics	occasionally	ToC	M
CQGra	IOP	Classical Quantum Gravity	often	ToC
Cryo	Elsevier	Cryogenics	occasionally	ToC
CryRp	AIP	Crystallography Reports	occasionally	ToC	M
CTM	IOP	Combustion Theory Modelling	often	ToC
DokPh	AIP	Physics - Doklady	occasionally	ToC
EJPh	IOP	European Journal of Physics	often	ToC
InfPh	Elsevier	Infrared Physics and Technology	often	abstracts
JAP	AIP	Journal of Applied Physics	often	ToC	M
JATP	Elsevier	Journal Atmospheric and Terrestrial Physics	occasionally	ToC
JChPh	AIP	Journal of Chemical Physics	often	ToC	M
JCoPh	AP	Journal of Computational Physics	occasionally	abstracts
JETP	AIP	JETP	occasionally	ToC	M
JETPL	AIP	JETP Letters	occasionally	ToC	M
JFS	AP	Journal of Fluids and Structures	occasionally	ToC
JGP	Elsevier	Journal of Geometry and Physics	occasionally	ToC
JLTP	OSA	Journal of Low Temperature Physics	occasionally	ToC	M
JLwT	OSA	Journal of Lightwave Technology	occasionally	ToC
JMagR	AP	Journal of Magnetic Resonance	occasionally	abstracts
JMMM	Elsevier	Journal of Magnetism and Magnetic Materials	occasionally	abstracts
JMPS	AIP	Journal of Mathematical Physics	often	ToC	M
JMoSp	AP	Journal of Molecular Spectroscopy	occasionally	abstracts
JNM	Elsevier	Journal of Nuclear Materials	occasionally	ToC
JPCM	IOP	Journal of the Physics of Condensed Matter	often	ToC
JPCRD	AIP	Journal of Physical and Chemical Reference Data	occasionally	ToC	M
JPCS	Elsevier	Journal of Physics and Chemistry of Solids	occasionally	ToC
JPhA	IOP	Journal of Physics A: Mathematical General	often	ToC
JPhB	IOP	Journal of Physics B: Atomic Molecular Physics	often	ToC
JPhD	IOP	Journal of Physics D: Applied Physics	often	ToC
JPhG	IOP	Journal of Physics G: Nuclear Physics	often	ToC
JRheo	AIP	Journal of Rheology	often	ToC	M
JSSCh	AP	Journal of Solid State Chemistry	occasionally	abstracts
JSV	AP	Journal of Sound and Vibration	often	ToC
JTePh	AIP	Journal of Technical Physics	occasionally	ToC	M
MedPh	AIP	Medical Physics	often	ToC	M
MSMSE	IOP	Modelling Simul. Mater. Sci. Eng.	often	ToC
MSSP	AP	Mechanical Systems & Signal Processing	occasionally	abstracts
NIMPA	Elsevier	Nuclear Instruments/Methods Physics Research A	often	abstracts
NIMPB	Elsevier	Nuclear Instruments/Methods Physics Research B	often	abstracts
Nanot	IOP	Nanotechnology	often	ToC
NDS	AP	Nuclear Data Sheets	occasionally	abstracts
Nonli	IOP	Nonlinearity	often	ToC
NuGeo	Elsevier	Nuclear Geophysics	occasionally	ToC
NuPhA	Elsevier	Nuclear Physics A	weekly	abstracts	E
NuPhB	Elsevier	Nuclear Physics B	weekly	abstracts	E
NuPhS	Elsevier	Nuclear Physics B Proceedings Supplements	monthly	abstracts	E
PAN	AIP	Physics of Atomic Nuclei	occasionally	ToC	M
PCEB	Elsevier	Physics and Chemistry of the Earth Part B	occasionally	ToC
PCEC	Elsevier	Physics and Chemistry of the Earth Part C	occasionally	ToC
PhFl	AIP	Physics of Fluids	often	ToC	M
PhLA	Elsevier	Physics Letters A	often	abstracts
PhLB	Elsevier	Physics Letters B	often	abstracts

Table 4: continued
Journal Source Full Name How Often Kind of Data Links ^a

PhPl AIP Physics of Plasmas often ToC M

PhR Elsevier Physics Reports often ToC

PhRvA AIP Physical Review A often ToC M

PhRvB AIP Physical Review B often ToC M

PhRvC AIP Physical Review C often ToC M

PhRvD AIP Physical Review D often ToC M

PhRvE AIP Physical Review E often ToC M

PhRvL AIP Physical Review Letters often ToC M

PhSS AIP Physics of the Solid State occasionally ToC M

PhT AIP Physics Today occasionally ToC M

PhyA Elsevier Physica A often ToC

PhyB Elsevier Physica B often abstracts

PhyC Elsevier Physica C often ToC

PhyD Elsevier Physica D often abstracts

PhyE Elsevier Physica E occasionally abstracts

PhyEd IOP Physics Education often ToC

PMB IOP Physics Medicine and Biology often ToC

PPCF IOP Plasma Physics and Controlled Fusion often ToC

PPN AIP Physics of Particles and Nuclei occasionally ToC M

PPNP Elsevier Progress in Particle and Nuclear Physics occasionally ToC

PQE Elsevier Progress in Quantum Electronics occasionally ToC

PSST IOP Plasma Sources Science Technology often ToC

QuSOp IOP Quantum Semiclassical Optics often ToC

RaPC Elsevier Radiation Physics and Chemistry often abstracts

RPPh IOP Reports on Progress in Physics often ToC

RvMP AIP Reviews of Modern Physics occasionally ToC M

Semic AIP Semiconductors occasionally ToC M

SeScT IOP Semiconductor Science Technology often ToC

SMaS IOP Smart Material Structures often ToC

SuScT IOP Superconductor Science Technology often ToC

SuMi AP Superlattices and Microstructures occasionally abstracts

TePhL AIP Technical Physics Letters occasionally ToC M

PhDT UMI University Microfilm, Inc. occasionally abstracts

WRM IOP Waves Random Media often ToC

**Table 4:** continued
Journal	Source	Full Name	How Often	Kind of Data	Links ^a
PhPl	AIP	Physics of Plasmas	often	ToC	M
PhR	Elsevier	Physics Reports	often	ToC
PhRvA	AIP	Physical Review A	often	ToC	M
PhRvB	AIP	Physical Review B	often	ToC	M
PhRvC	AIP	Physical Review C	often	ToC	M
PhRvD	AIP	Physical Review D	often	ToC	M
PhRvE	AIP	Physical Review E	often	ToC	M
PhRvL	AIP	Physical Review Letters	often	ToC	M
PhSS	AIP	Physics of the Solid State	occasionally	ToC	M
PhT	AIP	Physics Today	occasionally	ToC	M
PhyA	Elsevier	Physica A	often	ToC
PhyB	Elsevier	Physica B	often	abstracts
PhyC	Elsevier	Physica C	often	ToC
PhyD	Elsevier	Physica D	often	abstracts
PhyE	Elsevier	Physica E	occasionally	abstracts
PhyEd	IOP	Physics Education	often	ToC
PMB	IOP	Physics Medicine and Biology	often	ToC
PPCF	IOP	Plasma Physics and Controlled Fusion	often	ToC
PPN	AIP	Physics of Particles and Nuclei	occasionally	ToC	M
PPNP	Elsevier	Progress in Particle and Nuclear Physics	occasionally	ToC
PQE	Elsevier	Progress in Quantum Electronics	occasionally	ToC
PSST	IOP	Plasma Sources Science Technology	often	ToC
QuSOp	IOP	Quantum Semiclassical Optics	often	ToC
RaPC	Elsevier	Radiation Physics and Chemistry	often	abstracts
RPPh	IOP	Reports on Progress in Physics	often	ToC
RvMP	AIP	Reviews of Modern Physics	occasionally	ToC	M
Semic	AIP	Semiconductors	occasionally	ToC	M
SeScT	IOP	Semiconductor Science Technology	often	ToC
SMaS	IOP	Smart Material Structures	often	ToC
SuScT	IOP	Superconductor Science Technology	often	ToC
SuMi	AP	Superlattices and Microstructures	occasionally	abstracts
TePhL	AIP	Technical Physics Letters	occasionally	ToC	M
PhDT	UMI	University Microfilm, Inc.	occasionally	abstracts
WRM	IOP	Waves Random Media	often	ToC

$\textstyle \parbox{12cm}{$^{\mathrm{a}}$\space Letter codes describing what data are available.}$

Updates to the Astronomy and Instrumentation databases occur approximately every two weeks, or more often if logistically possible, in order to keep the database current. Recent enhancements to the indexing software have enabled us to perform instantaneous updates, triggered by an email containing new data (see ARCHITECTURE). Updates to the Physics database occurs approximately once every two months. As stated earlier, the Preprint database is updated nightly.

3.4 Data formats

The ADS is able to benefit from certain standards which are adhered to in the writing and submission practices of astronomical literature. The journals share common abbreviations and text formatting routines which are used by the astronomers as well. The use of TeX ([Knuth 1984]) and LaTeX ([Lamport 1986]), and their extension to BibTeX ([Lamport 1986]) and AASTeX ([American Astronomical Society 1999]) results in common formats among some of our data sources. This enables the reuse of parsing routines to convert these formats to our standard format. Other variations of TeX used by journal publishers also allows us to use common parsing routines which greatly facilitates data loading.

TeX is a public domain typesetting program designed especially for math and science. It is a markup system, which means that formatting commands are interspersed with the text in the TeX input file. In addition to commands for formatting ordinary text, TeX includes many special symbols and commands with which you can format mathematical formulae with both ease and precision. Because of its extraordinary capabilities, TeX has become the leading typesetting system for science, mathematics, and engineering. It was developed by Donald Knuth at Stanford University.

LaTeX is a simplified document preparation system built on TeX. Because LaTeX is available for just about any type of computer and because LaTeX files are ASCII, scientists are able to send their papers electronically to colleagues around the world in the form of LaTeX input. This is also true for other variants of TeX, although the astronomical publishing community has largely centered their publishing standards on LaTeX or one of the software packages based on LaTeX, such as BibTeX or AASTeX. BibTeX is a program and file format designed by Oren Patashnik and Leslie Lamport in 1985 for the LaTeX document preparation system, and AASTeX is a LaTeX-based package that can be used to mark up manuscripts specifically for American Astronomical Society (AAS) journals.

Similar to the widespread acceptance of TeX and its variants, the extensive use of SGML (Standard Generalized Markup Language, [Goldfarb & Rubinsky] 1991) by the members of the publishing community has given us the ability to standardize many of our parsing routines. All data gleaned off the World Wide Web share features due to the use of HTML (HyperText Markup Language, [Powell & Whitworth 1998]), an example of SGML. Furthermore, the trend towards using XML (Extensible Markup Language, [Harold 1999]) to describe text documents will enable us to share standard document attributes with other members of the astronomical community. XML is a subset of SGML which is intended to enable generic SGML to be served, received, and processed on the Web in the way that is now possible with HTML. The ADS parsing routines benefit from these standards in several ways: we can reuse routines designed around these systems; we are able to preserve original text representations of entities such as embedded accents so these entities are displayed correctly in the user's browser; and we are able to capture value-added features such as electronic URLs and email addresses for use elsewhere in our system.

In order to facilitate data exchange between different parts of the ADS, we make use of a tagged format similar to the "Refer" format ([Jacobsen 1996]). Refer is a preprocessor for the word processors nroff and troff which finds and formats references. While our tagged formats share some common fields (%A, %T, %J, %D), the Refer format is not specific enough to be used for our purposes. Items such as objects, URLs and copyright notices are beyond the scope of the Refer syntax. Details on our tagged format are provided in Table 5. Reading and writing routines for this format are shared by loading and indexing routines, and a number of our data sources submit abstracts to us in this format.