Foundations of Data Exchange

346 Pages·2014·1.986 MB·English

by  Arenas M., Barcelo P., Libkin L., Murlak F.

FOUNDATIONS OF DATA EXCHANGE
The problem of exchanging data between different databases with different
schemasisanareaofimmenseimportance.Consequentlydataexchangehasbeen
one of the most activeresearchtopics in databasesoverthe pastdecade.Founda-
tional questions related to data exchange largely revolve around three key prob-
lems: how to build target solutions; how to answer queries over target solutions;
and how to manipulate schema mappings themselves? The last question is also
known underthe name “metadata management”,since mappingsrepresent meta-
data,ratherthandatainthedatabase.
Inthisbooktheauthorssummarizethekeydevelopmentsofadecadeofresearch.
Part I introduces the problem of data exchangevia examples, both relational and
XML;PartIIdealswithexchangingrelationaldata;PartIIIfocusesonexchanging
XMLdata;andPartIVcoversmetadatamanagement.
Marcelo Arenas is an Associate Professor at the Department of Computer
ScienceatthePontificiaUniversidadCatolicadeChile.HereceivedhisPh.D.from
theUniversityofTorontoin2005.Hisresearchinterestsareindifferentaspectsof
databasetheory,suchasexpressivepowerofquerylanguages,databasesemantics,
inconsistency handling, database design, XML databases, data exchange, meta-
data management and database aspects of the Semantic Web. He has received
an IBM Ph.D. Fellowship (2004), seven best paper awards (PODS 2003, PODS
2005, ISWC 2006, ICDT 2010, ESWC 2011, PODS 2011 and WWW 2012) and
an ACM-SIGMOD Dissertation Award HonorableMention in 2006for his Ph.D.
dissertation “Design Principles for XML Data”. He has served on multiple pro-
gramcommittees,andsince2009hehasbeenparticipatingasaninvitedexpertin
theWorldWideWebConsortium.
Pablo BarcelóisanAssistantProfessorintheDepartmentofComputerSci-
ence at the University of Chile. He received his Ph.D. from the University of
Toronto in 2006. His main research interest is in the area of Foundationsof Data
Management,inparticular,querylanguages,dataexchange,incompletedatabases,
and, recently,graph databases.He has servedon programcommittees of some of
the majorconferencesin databasetheory andthe theoreticalaspectsofComputer
Science(PODS,ICDT,CIKM,STACS,SIGMOD).
Leonid LibkinisProfessorofFoundationsofDataManagementintheSchool
of Informatics at the University of Edinburgh. He was previously a Professor at
the University of Toronto and a member of research staff at Bell Laboratories in
Murray Hill. He received his PhD from the University of Pennsylvania in 1994.
His main research interests are in the areas of data managementand applications
of logic in computer science. He has written four books and over 150 technical
papers.He was the recipientofa Marie Curie ChairAward from the EU in 2006,
andwonfourbestpaperawards.Hehaschairedprogrammecommitteesofmajor
database conferences (ACM PODS, ICDT) and was the conference chair of the
2010 Federated Logic Conference. He has given many invited conference talks
and has served on multiple program committees and editorial boards. He is an
ACMfellowandafellowoftheRoyalSocietyofEdinburgh.
Filip Murlak is assistant professor at the Faculty of Mathematics, Informat-
ics,andMechanicsattheUniversityofWarsaw,Poland.Previouslyhewasresearch
fellowattheUniversityofEdinburgh.HereceivedhisPhDfromtheUniversityof
Warsawin2008.Hismainresearchareasareautomatatheoryandsemi-structured
data. He was the recipient of the best paper award at ICALP 2006, the Witold
LipskiPrizeforyoungresearchersin2008,andtheHomingPlusscholarshipfrom
the Foundation for Polish Science in 2010. He was co-chair of MFCS 2011 and
served on program committees of several database and theoretical computer sci-
enceconferences.
FOUNDATIONS OF DATA EXCHANGE
MARCELO ARENAS
Pontificia Universidad Católica de Chile
PABLO BARCELO´
Universidad deChile
LEONID LIBKIN
University of Edinburgh
FILIP MURLAK
Uniwersytet Warszawski, Poland
UniversityPrintingHouse,CambridgeCB28BS,UnitedKingdom
PublishedintheUnitedStatesofAmericabyCambridgeUniversityPress,NewYork
CambridgeUniversityPressispartoftheUniversityofCambridge.
ItfurtherstheUniversity’smissionbydisseminatingknowledgeinthepursuitof
education,learningandresearchatthehighestinternationallevelsofexcellence.
www.cambridge.org
Informationonthistitle:www.cambridge.org/9781107016163
©MarceloArenas,PabloBarceló,LeonidLibkinandFilipMurlak2014
Thispublicationisincopyright.Subjecttostatutoryexception
andtotheprovisionsofrelevantcollectivelicensingagreements,
noreproductionofanypartmaytakeplacewithoutthewritten
permissionofCambridgeUniversityPress.
Firstpublished2014
PrintedintheUnitedKingdombyCPIGroupLtd,CroydonCR04YY
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LibraryofCongressCataloguinginPublicationdata
ISBN978-1-107-01616-3Hardback
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accurateorappropriate.
v
ToMagdalena,MarcelitoandVanny,fortheirloveandsupport.
M.A.
ToSalvador,Gabiandmyparents.
P.B.
Tomyparents.
L.L.
Tomygrandparents,whochosetosendtheirkidstouniversity.
F.M.

Contents
Preface pagexi
PARTONE GETTINGSTARTED 1
1 Dataexchangebyexample 3
1.1 Adataexchangeexample 3
1.2 Overviewofthemaintasksindataexchange 9
1.3 Dataexchangevsdataintegration 11
2 Theoreticalbackground 12
2.1 Relationaldatabasemodel 12
2.2 Querylanguages 14
2.3 Incompletedata 18
2.4 Complexityclasses 21
2.5 Basicsofautomatatheory 27
3 Dataexchange:keydefinitions 29
3.1 Schemamappings 29
3.2 Solutions 30
3.3 Queryansweringandrewriting 31
3.4 Bibliographiccomments 32
PARTTWO RELATIONALDATAEXCHANGE 33
4 Theproblemofrelationaldataexchange 35
4.1 Keydefinitions 35
4.2 Keyproblems 39
5 Existenceofsolutions 43
5.1 Theproblemandeasycases 43
5.2 Undecidabilityforst-tgdsandtargetconstraints 44
5.3 Thechase 46
viii Contents
5.4 Weakacyclicityoftargetconstraints 49
5.5 Complexityoftheproblem 53
6 Goodsolutions 56
6.1 Universalsolutions 56
6.2 Existenceofuniversalsolutions 59
6.3 Canonicaluniversalsolutionandchase 65
6.4 Thecore 68
7 Queryansweringandrewriting 75
7.1 Answeringrelationalcalculusqueries 75
7.2 Answeringconjunctivequeries 76
7.3 Conjunctivequerieswithinequalities 78
7.4 Tractablequeryansweringwithnegation 81
7.5 Rewritabilityoverspecialsolutions 88
7.6 Non-rewritabilitytool:locality 91
8 Alternativesemantics 97
8.1 Universalsolutionssemantics 98
8.2 Closed-worldsemantics 102
8.3 Closed-worldsemanticsandtargetconstraints 112
8.4 Clopen-worldsemantics 121
9 EndnotestoPartTwo 124
9.1 Summary 124
9.2 Bibliographiccomments 125
9.3 Exercises 126
PARTTHREE XMLDATAEXCHANGE 133
10 TheproblemofXMLdataexchange 135
10.1 XMLdocumentsandschemas 135
10.2 KeyproblemsofXMLdataexchange 141
11 Patternsandmappings 143
11.1 Treepatterns:classificationandcomplexity 143
11.2 XMLschemamappingsandtheircomplexity 153
12 Buildingsolutions 158
12.1 Buildingsolutionsrevisited 158
12.2 Asimpleexhaustivesearchalgorithm 159
12.3 Nested-relationalDTDs 162
12.4 Thealgorithmforregularschemas 168
12.5 Thegeneralalgorithm 172
12.6 Combinedcomplexityofsolutionbuilding 178