Metadata for the Web From Discovery to Description

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Metadata for the WebFrom Discovery to Description

• CS 502 20020224
• Carl Lagoze Cornell University

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The fifteen Dublin Core Elements
http//dublincore.org/usage/terms/dc/current-eleme
nts/ http//dublincore.org
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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.

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What is the Dublin Core (1)

• A simple set of properties to support resource
  discovery on the web (fuzzy search buckets)?

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What is Dublin Core (2)?

• An extensible ontology for resource desciption?

Greater Functionality Cost
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What is the Dublin Core (3)?

• A cross-domain switchboard for interoperable
  metadata?

- projections to application-specific metadata
vocabularies
Switchboard
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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

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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.

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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.

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A Grammar of Dublin Core

• http//www.dlib.org/dlib/october00/baker/10baker.h
  tml
• 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...

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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.

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implied verb
one of 15 properties
property value (an appropriate literal)
DCCreator DCTitle DCSubject DCDate...
implied subject
Resource
has
property
X
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implied verb
one of 15 properties
property value (an appropriate literal)
DCCreator DCTitle DCSubject DCDate...
implied subject
Resource
has
property
X
qualifiers (adjectives)
optional qualifier
optional qualifier
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Resource
has
Subject
"Languages -- Grammar"
LCSH
Resource
has
Date
"2000-06-13"
Revised
ISO8601
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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 a hair color

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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"
Revised
ISO8601
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Incorrect Qualification
Resource
has
creator
Cornell University
affiliation
Resource
has
subject
pre-schoolers
audience
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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

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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 doesnt have metadata, metadata is
  just one resource annotating another

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Syntax AlternativesHTML

• Advantages
• Simple Mechanism META tags embedded in content
• Widely deployed tools and knowledge
• Disadvantages
• Limited structural richness (wont support
  hierarchical,tree-structured data or entity
  distinctions).

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Dublin Core in HTML

• http//www.dublincore.org/documents/2000/08/15/dcq
  -html/
• HTML constructs
• ltlinkgt to establish pseudo-namespace
• ltmetagt 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

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Dublin Core in HTML example
ltlink rel"schema.DC" href"http//purl.org/dc/ele
ments/1.1"gt ltmeta name"DC.Title"
content"Business Unusualgtltmeta nameDC.Title
langes contentnegocio inusualgt ltmeta
name"DC.Creator" content"Carl Lagoze"gt ltmeta
name"DC.Subject" content"bibliographic control
web cataloging "gt ltmeta name"DC.Date.Created"
scheme"W3CDTF" content"2000-10-23"gt ltmeta
name"DC.Format" content"text/html"gt ltmeta
name"DC.Identifier" content"http//lcweb.loc
.gov/lagoze_paper.html"gt
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Unqualified Dublin Core in XML
http//dublincore.org/documents/2002/09/09/dc-xml-
guidelines/
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Multi-entity nature of object description
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Attribute/Value approaches to metadata
The playwright of Hamlet was Shakespeare
Hamlet has a creator
Shakespeare
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run into problems for richer descriptions
The playwright of Hamlet was Shakespeare,who was
born in Stratford
Hamlet has a creator
Stratford
birthplace
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because of their failure to model entity
distinctions
Shakespeare
name
R1
R2
creator
birthplace
title
Stratford
Hamlet
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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.

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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.

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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

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Resource-centric Metadata
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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)

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Putting metadata in its place
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Query engine architecture space