LC Classification as linked data

0.14 MB·English

by  Kevin Ford

Library of Congress Classification as
linked data
KevinFord
What is linked data
TheLibraryofCongresshaspublishedaselectnumberofclasses
fromtheLibraryofCongressClassification(LCC)systemaslinked
dataasanewofferingofitsLinkedDataService,1commonlyknown
asid.loc.gov. Theoffering,whilestillconsideredabetaproject,pro-
videsURIsforresourcesthatrepresentasimplifiedversionofthe
underlyingdatafoundinthesourceMARCClassificationrecords.
The beta service also furnishes URIs for classification number re-
sourcesthateitherderivedirectlyfromtheunderlyingdataorare
theresultofasynthesisbetweenascheduleresourceandatablere-
source.AlthoughthedataarepresentedinMADS/RDF2andSKOS3
whereappropriate,LCCaslinkeddataisaccompaniedbyasmall
LCC ontology to more accurately describe the types of classifica-
tionresourcesandtherelationshipsbetweenthem,especiallywhere
MADS/RDFandSKOSClassandPropertydefinitionswereseenas
insufficient. ThispaperexploresthepublicationofLCCaslinked
dataandtheaccompanyingontologybycontextualizingthemwith
1http://id.loc.gov.
2http://www.loc.gov/mads/rdf.
3http://www.w3.org/2004/02/skos.
JLIS.it.Vol.4,n.1(Gennaio/January2013).
DOI:10.4403/jlis.it-5465
K.Ford,LibraryofCongressClassificationaslinkeddata
respecttoprioreffortsrepresentingLCCaslinkeddata,representing
Deweyaslinkeddata,andtheappropriatenessofSKOSforlibrary
classificationdata,especiallygiventhehistoricalneedforadistinct
MARCformatforClassification.
TheLibraryofCongressclassificationsystemhasexistedsincethe
latenineteenthcentury“toorganizeandarrangethebookcollec-
tionsoftheLibraryofCongress”(LibraryofCongressClassification).
The system is organized into twenty-one classes, most of which
arefurtherdividedintosubclasses. Eachclassrepresentsafieldof
knowledge,suchasArt,Law,orHistory. Eachsubclassisfurther
dividedintomorespecifictopicsthatbasicallyadheretoahierarchi-
calrepresentationofthefieldofknowledge. Likemostclassification
systems,LCCissubject-based. Theresulting“number”,therefore,
representsadistincttopicwithinthefieldofknowledge.Fordecades
LCC has been printed, bound, and distributed (at cost, basically)
andstillistoday. Onemayacquire,foraprice,theentire41-volume
setoronemaychooseindividualclassesorschedules. LCCisalso
accessibleviaClassificationWeb,4whichisasophisticatedwebappli-
cationdesignedtoassistcatalogerswiththeassignmentandcreation
ofLCCclassificationnumbers. Itisofferedasasubscriptionservice
for which LC charges a fee. Also for cost (basically), the Library
of Congress Classification is available in MARC21 format and is
madeavailableasabulkdownload, withperiodicupdates, from
theLibrary’sCatalogingandDistributionService. Notably,theraw
data, thoughavailable, requirespurchaseandisnotpresentedin
accordancewithlinkeddatamethodsandprinciples.
TheLibraryofCongressClassificationaslinkeddatadoeshavea
history,albeitashortandlittleknownone. KarenCoylelaboriously
scrapedthefirstfourlevels(moreorless)ofallLCClassification
classesfromPDFdocumentshostedontheLCwebsitetoaplain
4https://classificationweb.net.
JLIS.it. Vol.4,n.1(Gennaio/January2013).Art.#5465 p.162
JLIS.it.Vol.4,n.1(Gennaio/January2013)
textfile(thatis,somethingfarmoreaccessibleformachines)and
uploaded the resulting text file to archive.org.5 This work dates
to, and therefore the data predates, September 2007.6 The PDF
documents,whicharestillavailable(thoughperhapsupdatedsince),
presentadetailedoutlineofLCC.EdSummersthentookthetextfile,
generatedabasicSKOSRDFrepresentationfromit,anddevelopeda
verysimplewebsitewherehepublishedtheSKOSdata.7 Thiswork
waslittlepublicized,butitisstillactiveandaccessible. Summers’s
codeisonGitHub.8
Coyle’stextfilesimplyliststheclasses(A,B,C,andsoon)andthe
firstthreelevels,ifappropriate,ofeachsubclass(AC,AE,AG,and
soon). Theconcept’slabelatanygivenlevelismatchedwiththe
classnumber. BecauseonlythefirstfewlevelsofLCCareoutlined,
mostclassificationnumbersrepresentarangeofmorespecifictopics.
Missing–nearlyuniversally–fromthedetailedoutlinearelanguage-
specific divisions within topics, temporal divisions within topics,
andformdivisionswithintopics,inadditiontosimplygreatergran-
ularity and specificity, such as the distinction between “General
works”and“Specialtopics.” FromCoyle’stextfile,Summersgen-
eratedaskos:ConceptResourceforeachclassificationnumberand
associatedlabel.Hetookeachclassificationnumberandappendedit
toabaseHTTPURI(inanamespacehecontrols)tocreateanunique
identifierfortheresourceandhemadethelexicallabelforthetopic
(andclassnumber)theskos:prefLabel. Hegeneratedskos:broader
andskos:narrowerrelationshipsbetweenclassificationtopicswhen
theclassificationnumberrepresentedanencompassingrangeora
morespecificrangerespectively. Summerscreatedsomethingakin
5http://ia600304.us.archive.org/0/items/LcClassificationA-z/lc_class.txt.
6http://ia600304.us.archive.org/0/items/LcClassificationA-z/
LcClassificationA-z_meta.xml.
7http://inkdroid.org/lcco.
8https://github.com/edsu/lcco.
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K.Ford,LibraryofCongressClassificationaslinkeddata
to an LCSH-like pre-coordinated heading with the labels of nar-
rowertopics(i.e. thosethatfitcontextuallywithbroadertopics): the
skos:prefLabelofnarrowertopicscontainsthelabelsofitsbroader
relations, thelabelsofwhichareseparatedbytwohyphens. The
datacollectedbyCoyle,whichmayhavebeenallthatwasreason-
ablypossibletocollect,werelimitedtoaclassnumber,label,and
hierarchy. ThefirstthreelevelsoftheDeweyDecimalClassification
system–theDeweySummaries–havebeenavailableaslinkeddata
since2009.9 OCLCpublishedthefullDeweyDecimalClassification
aslinkeddatainSummer2012. AswithSummers’sdesign, each
topicisaskos:Conceptwithbroaderornarrowerrelationstoany
giventopic’shierarchicalrelatives.PublishedasitwasbyOCLC,the
availabledataarericher,includinginformationaboutprovenance
and licensing (no fewer than four statements for each Concept),
creationandmodificationtimes,amongafewothers. UnlikeSum-
mers’sdesign,OCLCreservedtheskos:prefLabelexclusivelyforthe
lexicallabelofthegivenConcept–broaderrelationsarenotstrung
togetherwiththetopic’slabeltocreatetheskos:prefLabel. OCLC’s
URIdesignpatternswarrantspecialmention. Painshavebeentaken
toembedsomesemanticsintotheURIpattern,reserving,essentially,
one namespace each for “non-information resources (abstract or
concretereal-worldobjects),genericresources,andtheirrepresenta-
tions”(OCLC). AlthoughsomeoftheURIexamplesdonotappear
tofunctionpresently,thefocusonURIcompositionandtheneed
torepresentavarietyofdifferentresourcetypesbearsontherep-
resentationofallaspectsofpublishingclassificationsystemssuch
asDDCandLCCaslinkeddata.10 Adiversenumberofresource
typesarealsoveryrelevanttoLCC.Inadditiontotheembedded
semanticsintheDeweyURIs,thisissuereceivedgreaterelucidation
9http://dewey.info.
10Theactualserviceathttp://dewey.infofeaturesdiverseURIpatterns, allof
whichappeartofunction,foralltypesofinformationresources.
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byPanzerandZengintworelatedpublications(PanzerandZeng;
Zeng,Panzer,andSalaba).
Theauthorsexploredhowtomodelclassificationschemes(notably
DDC) in SKOS. Among other findings, the authors discuss how
classification systems include “assignable” and “non-assignable”
concepts. InDDC,anexampleofanon-assignableconceptisacen-
teredentry,oraclassificationnumberrangeorspanforwhichthere
arelikelyanumberofmorespecifictopicsand,therefore,specific
numbers. In LCC, this is referred to as a range. There is also the
issue,asPanzerandZengnote(2009),ofsynthesizedconcepts(a
classificationnumberandtopicthatarearesultofcombiningtwo
conceptsintheclassificationsystem)andnon-synthesizedconcepts.
Oneriskssomesemanticincoherencywhenattemptingtomodelall
thesetypesofthings,andtoestablishappropriaterelationshipsbe-
tweenthem,purelyinSKOS.PanzerandZengconsideredtheneed
tocreate,minimally,anextensiontothecoreSKOSvocabulary,butit
wasclearthatanaltogetherseparateattemptmightbenecessary,in
anamespaceentirelydistinctfromaSKOSone,tocorrectlycapture
thesemanticsandrelationships.Thesesameissuesalsomaterialized
duringtheprocessoftryingtorepresentLCCinSKOS.
SKOS – the Simple Knowledge Organization System – is de-
signed“tosupporttheuseofknowledgeorganizationsystems(KOS)
suchasthesauri, classificationschemes, subjectheadinglistsand
taxonomieswithintheframeworkoftheSemanticWeb”.11 SKOS
hasproventobeextremelyversatileandeffectiveatrepresenting
thesauri,subjectheadinglists,andtaxonomies(though,inpartasa
resultofbeingintentionallysimple,therecanbesomelossofgranu-
laritywithrespecttolibrarydata). Infact,datarepresentedusing
theMARCFormatforAuthoritydata,suchassubjectheadinglists
likeLCSH,mapeffortlesslytoSKOS.Thisisseenreadilyandsimply
11http://www.w3.org/2004/02/skos.
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K.Ford,LibraryofCongressClassificationaslinkeddata
whendecomposingaMARCAuthorityrecordintoMADS/RDFand
SKOS.ForMARCAuthority,avalid(i.e. notdeprecated)authority
recordistheConcept. The1XX-themainheading-becomesthe
authoritativeorpreferredlabel. MADS/RDFprovidesameansto
capturethetypeofconcept,beitaTopic,Geographic,GenreForm,or
Temporalnotion,andafewothers. MADS/RDFalsoprovidessup-
portforbetterrepresentationofpre-coordinatedheadings. MARC
Authority4XXfieldsarevariantoralternatelabels. 5XXfieldsrep-
resentvariousrelationshipsbetweenterms,ofwhichbroaderand
narrowerrelationshipsarethemostpopular. MADS/RDFadded
afewadditionalrelationships,suchasthoseneededtoaccurately
recordconnectionsbetweenearlierorlaterestablishedconcepts,and
anewresourcetypetoclearlydenotedeprecatedresources. Anum-
berofnotefieldsdefinedinMARCAuthorityalsohaveone-to-one
mappingstoMADS/RDFandSKOS.ButMADS/RDFandSKOS
classesandpropertieshavebeenfarlessamenabletoclassification
data, or at least to library-specific classification systems such as
DDCandLCC.12ThisisessentiallythedifficultyPanzerandZeng
encounteredduringtheirresearchanditisthesameencountered
whenattemptingtopublishLCCaslinkeddata. Atleastwhenit
comestolibraryclassificationsystemssuchasDDCandLCC,thisis
unsurprising.
The influential consideration here lies with the MARC21 format
forClassification.13 Morespecifically,itsveryexistence. Formally
butprovisionallypublishedinJune1990,theMARC21Formatfor
12Thisprobablyhastodoalottodowiththerelativecomplexityofclassification
systems,especiallywithrespecttohowclassificationnumbersareconstructed,when
comparedtothesaurior“subjectheadinglists;”theaggregateexpertiseoftheSKOS
designersandmembersoftheworkinggroupwithrespecttoclassificationsystems;
and,partlyasanaturalextensionofthepreviouspoint,acertainamountofpartiality
andattentiongivento,andinfavorof,thesauriand“subjectheadinglists”during
thedevelopmentofSKOS.
13http://www.loc.gov/marc/classification.
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JLIS.it.Vol.4,n.1(Gennaio/January2013)
Classificationwasspecificallydevelopedtofacilitatetheexchange
and printing of classification data, most notably LCC and DDC
(Guenther). Importantly, the new MARC format was, however,
theresultofanattempttomodifytheMARCformatforAuthority
data(thisworkstartedin1987/1988). Afteridentifyingmostofthe
changes that would be required of the MARC Authority format,
a draft of the proposed changes was presented to the committee
overseeingchangestotheMARCformats(MARBI).Followingthis
review,andtheearlydevelopmentperiodgenerally,itwasclearthat
“there was less overlap with the authority format than originally
anticipated,and... [theMARCAuthority]codesandconventions
weretooconstraining”(Guenther). Theproposalforclassification
datawasrewrittentobeaseparateformat,whichwouldbecome
theMARCFormatforClassificationby1991.
TheMARCFormatforClassification–anditsdevelopmentprocess
–tookintoconsiderationtheverysamesemanticdifficultiesencoun-
teredbyPanzerandZeng,andthepresentauthor,whenfacedwith
“skosifying”complexlibraryclassificationdata,andadifficultythat
iscompoundedbytheunsuitablenatureoftheRDFdataelement
semantics. TheMARCFormatforClassificationcanrepresentclass
schedulesandtables,neitherofwhichisnecessarilyassignableasis.
Theformatcanrepresentrangesandhierarchy. Naturally,ithasfull
supportfornotesandindexterms. ButSKOSsemanticsarenotrich
enoughthistypeofinformation. Thatsaid,SKOScanreasonably
represent(assignable)classificationtopicsandevenclassnumber
ranges.Itiswiththisinformationinmind,andthebackgroundwork
byPanzerandZeng,thatitwasdecidedtopresentLCCaslinked
dataasmuchaspossibleinMADS/RDFandSKOSbuttodefinea
smallvocabularyinOWLtofaithfullyrepresentLCC-specificdata
anddataelementswhereMADS/RDFandSKOSfallshort.14
14http://id.loc.gov/ontologies/lcc.
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K.Ford,LibraryofCongressClassificationaslinkeddata
Although there are a few ontological constraints on the data,
constraintsdonotpresentlyextendtohowthedataareused. For
example, while it could be possible to infer “assignable” versus
“non-assignable”resourcesfromtheintersectionofselectClasses
in the ontology, this type of modeling has not been undertaken.
As such, it is an experimental offering that attempts to make no
semanticrestrictionsonitsusebutwhichstrivestorepresentthe
derivedandunderlyingdataaccurately.Theontologyisalsospecific
to LCC; it makes no attempt to model data elements specific to
otherclassificationsystems, suchasDDC.Also, thoughitwould
beunwisetoruleoutOCLCdevelopinganontologyforDDC,the
explicitdeclarationofclassesinthesmallLCContologytransfersthe
semanticsembeddedindewey.infoURIstothedataitself. (“Smart”
URIsandcleardatasemanticsarenotmutuallyexclusiveandcould,
infact,becomplementary.) AselectnumberofLibraryofCongress
ClassificationclassesareavailablefromLC’slinkeddataService,15
commonlyknownasid.loc.gov.16 Thisoffering-atthetimeofthis
publication - is very much a beta offering. During this stage, the
dataanditsrepresentationaresubjecttochange,especiallyasmore
islearnedabouthowthedataisusedandbetterwaysforittobe
represented are determined or developed. Nevertheless, it is an
attemptnotonlytopublishanRDFrepresentationoftheunderlying
data used to construct classification numbers but also to publish
the classification numbers themselves. To this end, an effort has
beenmadetoapplythetablestoschedules,therebysynthesizinga
classificationnumber,asappropriate.
In order not to become too mired in MADS/RDF 17 and SKOS 18
semanticsandrestrictions,everythingisaMADS/RDFAuthority
15http://id.loc.gov.
16http://id.loc.gov/ontologies/lcc.html.
17http://www.loc.gov/mads/rdf.
18http://www.w3.org/2004/02/skos.
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andSKOSConcept,withtheexceptionofIndexTerms,whichcan
beinterpretedasvariants. TheyarethereforeinstantiatedasMAD-
S/RDFVariantsandSKOS/XLAlternateLabels. Theauthoritative
label-thepreferredlabelandthetightlycontrolledterm-isreserved
forthemaincaptionorterm. ThisisthereforesimilartohowOCLC
createdDeweyresourcesandadeparturefromhowSummerspre-
sentedthedata. Thefulllexicallyrepresentedhierarchythatone
findsinthesourceMARCrecordsisrecordedsimplyasanrdfs:label
so that it is still available for parsing and potentially for display
purposes. The classes and properties in the LCC ontology, there-
fore,aretherealcarriersofdistinctionbetweenLibraryofCongress
Classificationresourcespublishedatid.loc.gov.19 TheLCContology
provides a way to describe the “underlying data,” which is a ref-
erencetothedataonewouldfindinaMARCclassificationrecord.
DataintheMARCclassificationrecordincludeinformationabout
classification-specificresourcetypessuchastablesandschedules,
anddatadescribedetailsabouthowtoapplytablenumberstobase
numberstogenerateandassignableclassificationnumber. Assuch,
theLCContologydefinesClassesandPropertiessufficientenough
toaccuratelyrepresentLCCdatainRDFandsufficientenoughto
synthesize class numbers from schedules when and however ap-
propriate. TheontologyisasignificantsimplificationoftheMARC
Classificationcodes,dataelementdefinitions,andconventions. One
suchsimplificationtouchesontheidentificationofdifferenttypesof
rangesdefinedinMARCClassification. Becausethereappearstobe
nomeaningfuldistinctionbetweenaMARCSummaryRangeand
MARCDefinedRangewithrespecttotheirrepresentationinRDF,
specificallyforLCC,thesetypesaresimplyanLCCRange. Onthe
19Ihaveendeavoredtocapitalizetheword“Class”(andProperty)whenreferring
toanOWLorRDFClass(orProperty).Wheneverreferencinganentityassociated
directlywithLCC-suchasclassificationnumber,LCCclass,classschedule,orclass
number-Ihavepresentedthewordinalllowercaseletters.
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K.Ford,LibraryofCongressClassificationaslinkeddata
otherhand,itwasdeemednecessarytodefineanadditionalTable
type-aGuideTable-wheretheMARCClassificationformatmade
nocleardistinctionbetweenthetwo. AGuideTableishierarchically
thebroadesttableconceptandcarriestheTableRule,whichisthe
instructionneededtosynthesizeaclassificationnumberbetweenan
LCCScheduleandanLCCTable. ThesmallLCContologyincludes
ClassesforaSchedule,Range,Table,GuideTable,andTableRule,
allofwhicharetypesofresourcesthataresomewhatuniquetoclas-
sificationschemes. Additionally, classification-specificproperties
havebeendefinedthatrelatetheseclassestoeachother,suchasone
thatrelatesaTabletoitsGuideTableoranotherthatrelatesaGuide
TabletooneormoreSchedules,towhichtheGuideTablemayapply.
Atallothertimes,MADS/RDF,whichisfullymappedtoSKOS,is
employed(alldataare,ofcourse,alsooutputtedasSKOS).Naturally,
theseTable,GuideTable,andScheduleresourcesare“underlying
data”andaregenerallyconsideredtobe“non-assignable,”thatis
theyareresourcesthatshouldnotbeusedtodescribeanotherre-
source,suchasabibliographicone. Becausetheseresourcesoften
haveaone-to-onerelationshipwithanunderlyingMARCClassifi-
cationrecord,theLCCNoftheunderlyingrecordhasbeenusedas
partoftheURIscheme. AnLCCNthatbeginswith“CF”represents
aschedule;onethatbegins“CT”representsaGuideTableorTable.
However,whenclassificationresourcesaredescribedwiththeClass-
NumberOWLClass,theresourcecouldbedescribedasassignable.
TheURIsfortheseresourcesendinaclassificationnumberorrange.
AClassNumberresourcemaybeanLCCRangeoraMADS/RDF
Topic. Theformer-anLCCRange-generallyrepresentsagroupof
conceptshierarchicallyrelatedtothebroaderconceptrepresented
bytherange.Ofcourse,rangesarenotassignablewhentraditionally
assigningclassificationnumberstophysicalbibliographicresources.
MADS/RDFTopicwasusedwhentheresourcerepresentedasingle,
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