Metadata for the Web From Discovery to Description

1. Metadata for the WebFrom Discovery to Description CS 502 – 20020224 Carl Lagoze – Cornell University

2. The fifteen Dublin Core Elements http://dublincore.org/usage/terms/dc/current-elements/ http://dublincore.org

3. A Pidgin for Digital Tourists • Metadata is language • Dublin Core is a small and simple language -- a pidgin -- for finding resources across domains. • Speakers of different languages naturally "pidginize" to communicate • E.g., tourists using simple phrases to order beer ("zwei Bier bitte" "dva pivo" "biru o san bai"...) • We are all "tourists" on the global Internet.

4. Domain Independent view What is the Dublin Core (1) • A simple set of properties to support resource discovery on the web (fuzzy search buckets)?

5. What is Dublin Core (2)? • An extensible ontology for resource desciption? Greater Functionality & Cost

6. MARC Dublin Core IMS INDECS What is the Dublin Core (3)? • A cross-domain switchboard for interoperable metadata? - projections to application-specific metadata vocabularies Switchboard

7. Dublin Core Qualifiers • From fuzzy buckets to more specific description • Model of “graceful degradation” • Support both simplicity and specificity • Intra-domain and inter-domain semantics

8. Varieties of qualifiers: Element Refinements • Make the meaning of an element narrower or more specific. • Narrowing implies an is a relationship • a "date created“ is a "date“ • an "is part of relation“ is a "relation“ • If your software does not understand the qualifier, you can safely ignore it.

9. Varieties of Qualifiers: Value Encoding Schemes • Says that the value is • a term from a controlled vocabulary (e.g., Library of Congress Subject Headings) • a string formatted in a standard way (e.g., "2001-05-02" means May 3, not February 5) • Even if a scheme is not known by software, the value should be "appropriate" and usable for resource discovery.

10. A Grammar of Dublin Core • http://www.dlib.org/dlib/october00/baker/10baker.html • By design not as subtle as mother tongues, but easy to learn and extremely useful in practice • Pidgins: small vocabularies (Dublin Core: fifteen special nouns and lots of optional adjectives) • Simple grammars: sentences (statements) follow a simple fixed pattern...

11. Example Dublin Core statements • Resource has Title 'Grammar of Dublin Core'. • Resource has Creator 'Tom Baker'. • Resource has Subject 'Metadata'. • Resource has Relation http://foo.org/file.htm.

12. implied verb one of 15 properties property value (an appropriate literal) DC:Creator DC:Title DC:Subject DC:Date... implied subject Resource has property X

13. implied verb one of 15 properties property value (an appropriate literal) DC:Creator DC:Title DC:Subject DC:Date... implied subject Resource has property X qualifiers (adjectives) [optional qualifier] [optional qualifier]

14. Resource has Subject "Languages -- Grammar" LCSH Resource has Date "2000-06-13" ISO8601 Revised

15. Dumb-Down Principle for Qualifiers • The fifteen elements should be usable and understandable with or without the qualifiers • Qualifiers refine meaning (but may be harder to understand) • Nouns can stand on their own without adjectives • If your software encounters an unfamiliar qualifier, look it up -- or just ignore it! • "has a“ relations break the model • E.g., a creator has ahair color

16. Test for “good““ qualifiers: cover and ask: -- Does the statement still make sense? -- Is it still correct? Resource has Subject "Languages -- Grammar" LCSH Resource has Date "2000-06-13" ISO8601 Revised

17. “Incorrect” Qualification Resource has creator “Cornell University” affiliation Resource has subject “pre-schoolers” audience

18. Open questions in this model • Are uncontrolled and unconstrained values really useful for discovery? • Is it possible for an organization (DCMI) to control the evolution of a language? • How can "simple discovery metadata" be combined with complex descriptions? Is there a notion of graceful degradation? • Can DC serve as a lingua franca (mapping template) among more complex models

19. Models for Deploying Metadata • Embedded in the resource • low deployment threshold • Limited flexibility, limited model • Linked to from resource • Using xlink • Is there only one source of metadata? • Independent resource referencing resource • Model of accessing the object through its surrogate • Resource doesn’t ‘have’ metadata, metadata is just one resource annotating another

20. Syntax Alternatives:HTML • Advantages: • Simple Mechanism – META tags embedded in content • Widely deployed tools and knowledge • Disadvantages • Limited structural richness (won’t support hierarchical,tree-structured data or entity distinctions).

21. Dublin Core in HTML • http://www.dublincore.org/documents/2000/08/15/dcq-html/ • HTML constructs • <link> to establish pseudo-namespace • <meta> for metadata statements • name attribute for DC element (DC.element.ER) • content attribute for element value • scheme attribute for encoding scheme or controlled vocabulary • lang attribute for language of element value

22. Dublin Core in HTML example <link rel="schema.DC" href="http://purl.org/dc/elements/1.1"> <meta name="DC.Title" content="Business Unusual”><meta name=“DC.Title” lang=“es” content=“negocio inusual”> <meta name="DC.Creator" content="Carl Lagoze"> <meta name="DC.Subject" content="bibliographic control web cataloging "> <meta name="DC.Date.Created" scheme="W3CDTF" content="2000-10-23"> <meta name="DC.Format" content="text/html"> <meta name="DC.Identifier" content="http://lcweb.loc.gov/lagoze_paper.html">

23. Unqualified Dublin Core in XML http://dublincore.org/documents/2002/09/09/dc-xml-guidelines/

24. Photographer Computer artist Camera type Software Multi-entity nature of object description

25. subject implied verb metadata noun literal metadata adjective Playwright “Shakespeare” dc:creator.playwright R1 dc:title “Hamlet” Attribute/Value approaches to metadata… The playwright of Hamlet was Shakespeare Hamlet has a creator Shakespeare

26. “Shakespeare” dc:creator.playwright R1 dc:creator.birthplace “Stratford” …run into problems for richer descriptions… The playwright of Hamlet was Shakespeare,who was born in Stratford Hamlet has a creator Stratford birthplace

27. …because of their failure to model entity distinctions “Shakespeare” name R1 R2 creator birthplace title “Stratford” “Hamlet”

28. Applying a Model-Centric Approach • Formally define common entities and relationships underlying multiple metadata vocabularies • Describe them (and their inter-relationships) in a simple logical model • Provide the framework for extending these common semantics to domain and application-specific metadata vocabularies.

29. Events are key to understanding resource complexity? • Events are implicit in most metadata formats (e.g., ‘date published’, ‘translator’) • Modeling implied events as first-class objects provides attachment points for common entities – e.g., agents, contexts (times & places), roles. • Clarifying attachment points facilitates understanding and querying “who was responsible for what when”.

30. ABC/Harmony Event-aware metadata ontology • Recognizing inherent lifecycle aspects of description (esp. of digital content) • Modeling incorporates time (events and situations) as first-class objects • Supplies clear attachment points for agents, roles, existential properties • Resource description as a “story-telling” activity

31. ? Resource-centric Metadata

32. “Orest Vereisky” “Leo Tolstoy” “Margaret Wettlin” "Moscow" “illustrator” “author” “translator” “1828” “1877” “1978” “creation” “translation” “Russian” “English” “Tragic adultery andthe search for meaningfullove” “Anna Karenina”

33. Breaking the metadata bottleneck Human vs. machine generation • Simple text scraping • HTML tags as hint • Other structural methods • Natural language methods and machine learning • Contextual methods • Google (text and image search)

34. Putting metadata in its place

35. Query engine architecture space