Big Data Management Question Paper

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Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Exposing Legacy Data to the Web of Data Big Data Management Alasdair J G Gray [email protected] EM 1.39 Material from: Juan F. Sequeda , Daniel P. Miranker , and Barry Norton https:// www.slideshare.net / juansequeda /rdb2-rdf-tutorial-iswc2013 Kenneth McLeod

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Materials released under CC-BY License You are free to: Share — copy and redistribute the material in any medium or format Adapt — remix, transform, and build upon the material for any purpose, even commercially. The licensor cannot revoke these freedoms as long as you follow the license terms. Under the following terms: Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. 2020 A.J.G. Gray – Big Data Management 2

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Outline What is OBDA? Mappings Direct Mapping R2RML Using Ontop 2020 A.J.G. Gray – Big Data Management 3 https:// www.researchgate.net /figure/Ontology-based-Data-Access_fig1_220575553

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Linked Data Web Large number of data sources Most converted from relational database Problem: Lots of legacy data stored in relational database, spreadsheets, etc How do we expose legacy data on the Web? 2020 A.J.G. Gray – Big Data Management 4 style.visibility

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Expose Relational Database as RDF 2020 A.J.G. Gray – Big Data Management 5 Bob

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Ontology Based Data Access (OBDA) Data Integration: Global Schema: Ontology Data Source(s): Database schema(s) Mapping between Ontology & Source(s) You can now apply Semantic Technologies E .g., reason over the ontology to infer new information Merge data that share IRIs Ontology Data Source Data Source Mappings … 2020 A.J.G. Gray – Big Data Management 6

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Direct Mapping 2020 A.J.G. Gray – Big Data Management 7

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Direct Mapping Input: Relational database Output: RDF representation of database Advantages Automatic process: no configuration Limitations Not linked to existing ontologies Relational model usually poor graph model 2020 A.J.G. Gray – Big Data Management 8

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Relational to RDF Mapping (R2RML) 2020 A.J.G. Gray – Big Data Management 9

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R2RML Mapping Input: Relational database Domain ontologies: target schema Output: RDF modelled using terms from the ontologies representing the database content Advantages Linked to ontologies: supports data reuse Good graph representation (if suitable ontologies are used) Limitations Requires human input to build mappings 2020 A.J.G. Gray – Big Data Management 10

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Mapping Languages Both Direct Mapping and R2RML are W3C standards Direct Mapping https://www.w3.org/TR/ rdb -direct-mapping/ (Sept 2012) R2RML https://www.w3.org/TR/r2rml/ (Sept 2012) RML generalises R2RML for CSV, XML, JSON, etc http:// rml.io / Both have several implementations https://www.w3.org/TR/rdb2rdf-implementations/ Standalone: D2RQ, Morph, RMLMapper , Ontop , Ultrawrap Data stores: Oracle, Virtuoso 2020 A.J.G. Gray – Big Data Management 11

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To materialise or not? Materialised RDF Virtual RDF 2020 A.J.G. Gray – Big Data Management 12

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To materialise or not? Materialise Exports data from source Updates on next ETL Queries run locally Virtual Data remains in source Reflects updates Queries rewritten over source(s) 2020 A.J.G. Gray – Big Data Management 13

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Direct Mapping 2020 A.J.G. Gray – Big Data Management 14

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Direct Mapping Result 2020 A.J.G. Gray – Big Data Management 15 Bob

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Primary Key IRIs 2020 A.J.G. Gray – Big Data Management 16

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Table and Attribute IRIs 2020 A.J.G. Gray – Big Data Management 17 Foreign Key Reference Attribute Table

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Direct Mapping Identifiers Need identifiers for Rows: Primary key mapped into IRI Blank node if no primary key Tables: Mapped into IRI Columns: Mapped into IRI Foreign Keys: Mapped into IRI IRI generated by appending to base IRI All strings URL encoded 2020 A.J.G. Gray – Big Data Management 18

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Table Triple 2020 A.J.G. Gray – Big Data Management 19

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Literal Triple 2020 A.J.G. Gray – Big Data Management 20

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Reference Triple (Foreign Key) 2020 A.J.G. Gray – Big Data Management 21

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Direct Mapping Summary W3C Standard Automatic mapping NULLs are not exported in RDF IRIs automatically generated from base IRI base:table base:table#attribute base:table#ref-attribute base:table#pkAttr = pkValue (; pkAttr = pkValue …) RDF represents relational schema Transform into ontology using SPARQL CONSTRUCT 2020 A.J.G. Gray – Big Data Management 22

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R2RML Mapping 2020 A.J.G. Gray – Big Data Management 23

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R2RML Mapping Result 2020 A.J.G. Gray – Big Data Management 24 Bob Bob

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Choosing a Target Ontology Search for existing ontology http:// lov.okfn.org Look for widely used ontology Find one that matches most of your terms Use same ontology as other sources that you are connecting the data to Can select terms from multiple ontologies Need to be aware of logical consequences of decisions 2020 A.J.G. Gray – Big Data Management 25

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FOAF: Friend of a Friend Vocabulary Widely used vocabulary Represents People Organizations 2020 A.J.G. Gray – Big Data Management 26 http:// xmlns.com / foaf /spec/

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‘Ugly’ vs ‘Cool’ IRIs 2020 A.J.G. Gray – Big Data Management 27

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R2RML Identifiers Control format of IRIs Avoid = signs which can cause some tools issues Predicate and type IRIs drawn from ontology Data instance IRIs use base IRI 2020 A.J.G. Gray – Big Data Management 28

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R2RML Mapping from base relation @prefix rr : <http://www.w3.org/ns/r2rml#> . @prefix foaf : <http:// xmlns.com / foaf /0.1/> . <TriplesMap1> a rr:TriplesMap ; rr:logicalTable [ rr:tableName "Person"]; rr:subjectMap [ rr:template "http:// www.ex.com /Person/p{id}" ; rr:class foaf:Person ] ; rr:predicateObjectMap [ rr:predicate foaf:name ; rr:objectMap [ rr:column "NAME"] ] . 2020 A.J.G. Gray – Big Data Management 29 Thing being mapped Subject IRI pattern Generates <http:// www.ex.com /Person/p1> rdf:type foaf:Person . Predicate IRI Object value from DB Generates <http:// www.ex.com /Person/p1> foaf:name ”Alice" .

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R2RML Mapping from view @prefix rr : <http://www.w3.org/ns/r2rml#> . @prefix foaf : <http:// xmlns.com / foaf /0.1/> . <TriplesMap2> a rr:TriplesMap ; rr:logicalTable [ rr:sqlQuery """SELECT ID, NAME FROM Person WHERE gender = 'F'"""]; rr:subjectMap [ rr:template "http:// www.ex.com /Person/p{id}" ; rr:class <http:// www.ex.com /Woman> ] ; rr:predicateObjectMap [ rr:predicate foaf:name ; rr:objectMap [ rr:column "NAME"] ] . 2020 A.J.G. Gray – Big Data Management 30 SQL query to extract data

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R2RML Mapping Summary W3C Standard Manually defined mapping Can bootstrap with Direct Mapping Learning curve for creating Tools available to support creation, e.g. Ontop SQL query to select-project-join base data Multiple mappings for same resource Deals with NULLs RDF in target ontology 2020 A.J.G. Gray – Big Data Management 31

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Ontop : Protégé Plugin Live demonstration! 2020 A.J.G. Gray – Big Data Management 32

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Protégé: OWL Ontology Editor 2020 A.J.G. Gray – Big Data Management 33 Widely used open source ontology editor We’ll cover it in detail next week Need to install ontop plugin File -> Check for plugins…

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Open Existing Ontology from URL: FOAF 2020 A.J.G. Gray – Big Data Management 34 Select File -> Open from URL Enter ontology URI http:// xmlns.com / foaf /spec/ Click OK

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Protégé with Ontop plugin 2020 A.J.G. Gray – Big Data Management 35 Ontop provides OBDA functionality https:// ontop.inf.unibz.it / Developed by Free University of Bozen Bolzano Documentation https:// github.com / ontop / ontop /wiki/ ObdalibOntoproPlugin

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Configure JDBC Connector 2020 A.J.G. Gray – Big Data Management 36 Open Protégé preferences File -> Preferences Click JDBC Drivers tab Enter details

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FOAF Ontology Summary 2020 A.J.G. Gray – Big Data Management 37 Provenance Number of axioms Number of classes Number of properties Complexity of ontology (DL expressivity) Namespaces

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FOAF Ontology Entities 2020 A.J.G. Gray – Big Data Management 38 Class hierarchy Class annotations Class description Property tabs Show similar details for properties

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Connect to MySQL Server 2020 A.J.G. Gray – Big Data Management 39 Click on Ontop Mappings Pane Click on Datasource manager Enter MySQL server details Database URL including database jdbc:mysql ://mysql-server-1.macs.hw.ac.uk/ajg33 Select driver Test connection Save the configuration Choose turtle

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Company Example: Employee Table 2020 A.J.G. Gray – Big Data Management 40 Table about employees We’re going to map this to foaf Note NULL in dateOfBirth

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Mapping Employee 2020 A.J.G. Gray – Big Data Management 41 Create mappings on Mapping manager Top box enter target ontology terms Include highlighting and error detection Middle box enter SQL to retrieve required data Note no date of birth in this mapping

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Mapping Employee Date of Birth 2020 A.J.G. Gray – Big Data Management 42 Create additional mapping for same resource Dealing with NULL Adding datatype declaration

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Querying with SPARQL: Problem 2020 A.J.G. Gray – Big Data Management 43 We have not started the reasoner Select Ontop reasoner Reasoner -> Ontop Start reasoner Reasoner -> Start reasoner

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Querying with SPARQL 2020 A.J.G. Gray – Big Data Management 44 Subset of SPARQL supported Must declare prefixes Can save queries Click + before entering query Give it a meaningful name

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Materialise as RDF file 2020 A.J.G. Gray – Big Data Management 45 Select Ontop -> Materialize triples… Choose Dump triples Select file format

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Summary 2020 A.J.G. Gray – Big Data Management 46

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Summary ODBA supports exposing variety of data sources to web of data Relational XML CSV Mappings relate source data to ontology Direct Mapping: automatic R2RML: Converts to existing ontology Ontop provides support for OBDA 2020 A.J.G. Gray – Big Data Management 47

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Data Integration 2018 Click to edit Master text styles Second level Third level Fourth level Fifth level A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master subtitle style 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master text styles 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Click to edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master text styles Click to edit Master text styles Second level Third level Fourth level Fifth level Click to edit Master text styles Click to edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level Click to edit Master text styles 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master subtitle style 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master subtitle style 2020 A.J.G. Gray – Big Data Management Click icon to add picture

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Click to edit Master title style Edit Master text styles Second level Third level Fourth level Fifth level Edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Edit Master text styles Edit Master text styles Second level Third level Fourth level Fifth level Edit Master text styles Edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Edit Master text styles Second level Third level Fourth level Fifth level Edit Master text styles 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click icon to add picture Edit Master text styles 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Click to edit Master subtitle style 2020 A.J.G. Gray – Big Data Management Click icon to add picture

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Click to edit Master title style Click to edit Master subtitle style 2020 A.J.G. Gray – Big Data Management Click icon to add picture Click icon to add picture

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Click to edit Master title style Click to edit Master subtitle style 2020 A.J.G. Gray – Big Data Management Click icon to add picture Click icon to add picture Click icon to add picture

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Click to edit Master title style Edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Click to edit Master title style Edit Master text styles Second level Third level Fourth level Fifth level 2020 A.J.G. Gray – Big Data Management ‹#›

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Highlight Juan’s tutorial from which most of the slides are taken Ontop live demonstration - ontop screenshots in slides - Connect company database using foaf Data Integration 2018 A.J.G. Gray – Big Data Management 1

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Data Integration 2018 A.J.G. Gray – Big Data Management 2

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Highlight that in Juan’s slides there is an error which has been corrected here. The name of Person 2 is Bob not Alice Data Integration 2018 A.J.G. Gray – Big Data Management 5

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More complex scenarios are possible C ould have two ontologies with two sources, joined a by (third) bridging ontology OR could have one ontology mapped onto two different sources 6

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Materialise Exports data from source Updates on next ETL Queries run locally Virtual Data remains in source Reflects updates Queries rewritten over source(s) Data Integration 2018 A.J.G. Gray – Big Data Management 12

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Shown IRIs all assume a base IRI Data Integration 2018 A.J.G. Gray – Big Data Management 15

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Single attribute primary key Composite attribute primary key Data Integration 2018 A.J.G. Gray – Big Data Management 16

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IRI generation follow a set of rules Data Integration 2018 A.J.G. Gray – Big Data Management 22

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Control format of IRIs Avoid = signs which can cause some tools issues Data Integration 2018 A.J.G. Gray – Big Data Management 27

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Highlight the following things in this order: Install Ontop plugin Configure JDBC driver Load foaf vocabulary from URL Establish database connection including database name Clarify - IRI vs namespace, - turtle abbreviation of triples, - object vs data property Data Integration 2018 A.J.G. Gray – Big Data Management 32

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Example data we will be mapping ER Diagrams 2018 F28DM Database Systems – A.J.G. Gray 40

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CC5212-1 Procesamiento Masivo de Datos 2014 Aidan Hogan Gray, Alasdair J G 969 2019-03-05T08:56:42Z 2006-08-16T00:00:00Z 2020-02-19T11:20:51Z

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lectures.thmx 20869 2488 Microsoft Macintosh PowerPoint Widescreen 488 47 13 6 0 false Fonts Used 8 Theme 2 Slide Titles 47 Arial Calibri Century Gothic Courier New Open Sans Times New Roman Wingdings Wingdings 2 1_hwu lectures Exposing Legacy Data to the Web of Data Materials released under CC-BY License Outline Linked Data Web Expose Relational Database as RDF Ontology Based Data Access (OBDA) Direct Mapping Direct Mapping Relational to RDF Mapping (R2RML) R2RML Mapping Mapping Languages To materialise or not? To materialise or not? Direct Mapping Direct Mapping Result Primary Key IRIs Table and Attribute IRIs Direct Mapping Identifiers Table Triple Literal Triple Reference Triple (Foreign Key) Direct Mapping Summary R2RML Mapping R2RML Mapping Result Choosing a Target Ontology FOAF: Friend of a Friend Vocabulary ‘Ugly’ vs ‘Cool’ IRIs R2RML Identifiers R2RML Mapping from base relation R2RML Mapping from view R2RML Mapping Summary Ontop: Protégé Plugin Protégé: OWL Ontology Editor Open Existing Ontology from URL: FOAF Protégé with Ontop plugin Configure JDBC Connector FOAF Ontology Summary FOAF Ontology Entities Connect to MySQL Server Company Example: Employee Table Mapping Employee Mapping Employee Date of Birth Querying with SPARQL: Problem Querying with SPARQL Materialise as RDF file Summary Summary false false false 16.0000