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Introduction to linked data Gordon Dunsire Presented at the Cataloguing and Indexing Group Scotland seminar Linked data and the Semantic Web: what have.

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Presentation on theme: "Introduction to linked data Gordon Dunsire Presented at the Cataloguing and Indexing Group Scotland seminar Linked data and the Semantic Web: what have."— Presentation transcript:

1 Introduction to linked data Gordon Dunsire Presented at the Cataloguing and Indexing Group Scotland seminar Linked data and the Semantic Web: what have libraries got to do with it?, Edinburgh, National Library of Scotland, 17 June 2011

2 Overview Relational records Influence of RDA vocabularies Disaggregated, distributed records Logical conclusion: simple metadata statement RDF Triples, etc. Linked data Chains, clusters

3 Title:Cataloguing is fun! Author:Mary MacDonald Content type: Carrier type: LCSH: microfiche text Cataloging Bibliographic record: 12345Name authority record: 8765 Heading:MacDonald, Mary Place of birth:Edinburgh LCSH authority record: 5432 Heading:Cataloging See also:Books RDA content type record: 1234 Term:text Definition:Content expressed through a form of notation for language intended to be perceived visually. RDA carrier type record: 5432 Term:microfiche Definition:A sheet of film bearing a number of microimages in a two- dimensional array

4 Title:Cataloguing is fun! Author: Content type: Carrier type: LCSH: Bibliographic record: Name authority record: 8765 Heading:MacDonald, Mary Place of birth: Author8765Place of birth HeadingMacDonald, Mary9876NameEdinburgh 9876Country4567 Stop! Ambiguous: link not safe. Identifier: ok to link.

5 Linked data is not a new idea! It extends concepts of authority control Preferred labels Change once; link many times Re-use of metadata More than one attribute associated with a heading E.g. Place of birth of person with name heading Concepts can be applied to authority records As well as bibliographic description records Full extension leads to record dis-aggregation All records in bibliographic control systems

6 Linked data and RDF Resource Description Framework (RDF) Designed for machine-processing of metadata at global scale 24/7/365 Trillions of operations per second Everything must be dis-ambiguated Machines are dumb Simplicity helps! Machine-readable identifiers

7 RDF triple Metadata expressed as atomic statements A simple, single, irreducible statement The title of this book is Cataloguing is fun! Constructed in 3 parts Triple The title of this book is Cataloguing is fun! Subject of the statement = Subject: This book Nature of the statement = Predicate: has title Value of the statement = Object: Cataloguing is fun! This book – has title – Cataloguing is fun! subject – predicate - object

8 Identifiers Need unambiguous way of identifying each part of the triple for efficient machine- processing Human labels (This book, has title) no good Same thing, different labels; different things, same label Exploit the utility of the URL Machine-readable, regular syntax, unambiguous Uniform Resource Identifier (URI)

9 Uniform Resource Identifier Can be any unique combination of numbers and letters No intrinsic meaning; its just an identifying label Can look like a URL But does not lead to a Web page (in principle...) RDF requires the subject and predicate of triple to be URIs Object can be a URI, or a literal string (Cataloguing is fun!)

10 Namespaces URI can be constructed from a base plus a unique, identifying suffix + P1001 Base is known as a namespace Can be abbreviated by human programmer isbd = isbd:P1001 Machine expands abbreviation for processing

11 Everything as triples in RDF Every aspect of the metadata must be expressed in RDF to be machine-processable Metadata about real-world objects (books, people, etc.) Metadata about the predicates (definition, label, scope, etc.) Common predicates apply to many types of thing (human-readable label, etc.) High-level RDF namespaces (rdfs, owl, skos) RDF is expressed in RDF (bootstrap)

12 RDF properties Predicates are called properties in RDF Verbal part of the metadata statement E.g. A has title..., B is author of C, D is embodiment of E Properties link specific instances of two things A = a specific book, B = a specific person, etc.... = a specific label, character string, annotation => a literal Properties are the links in linked data, the pathways through the Semantic Web

13 Domains and ranges A property can specify the types of thing it links E.g. Bibliographic resources, Persons, Places, etc. Types of thing are RDF classes A domain is the class of the subject of the property E.g. The domain of is embodiment of is Expression (FRBR) A range is the class of the object of the property E.g. The range of is embodiment of is Manifestation (FRBR)

14 Inferencing RDF enables semantic inferencing Deducing additional, unstated triples from an existing statement or set of statements E.g. D is embodiment of E + (is embodiment of) has domain Expression => D is a Expression And D is embodiment of E + (is embodiment of) has range Manifestation => E is a Manifestation

15 The truth There is no test of veracity for a single triple in RDF Anybody can say Anything about Anything (AAA) Inferencing only tests for logical inconsistency E.g. If it results in E is a Manifestation + E is not a Manifestation Library linked data must choose and apply its properties/links with care To maintain our reputation for reliability, quality, etc. In a web of user-, machine-, and politically-generated metadata

16 Thank you To be continued...


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