Metadata for the Web From Discovery to Description

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Metadata for the WebFrom Discovery to Description

• CS 502 20020226
• Carl Lagoze Cornell University

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Co-existing Cost/Functionality Levels
Greater Functionality Cost
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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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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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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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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

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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
lt?xml version"1.0"?gt lt!DOCTYPE rdfRDF SYSTEM
"http//dublincore.org/2000/12/01-dcmes-xml-dtd.dt
d"gt ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/
22-rdf-syntax-ns" xmlnsdc"http//purl.
org/dc/elements/1.1/"gt ltrdfDescription
rdfabout"http//www.ilrt.bristol.ac.uk/people/cm
djb/"gt ltdctitlegtDave Beckett's Home
Pagelt/dctitlegt ltdccreatorgtDave
Beckettlt/dccreatorgt ltdcpublishergtILRT,
University of Bristollt/dcpublishergt
ltdcdategt2000-06-06lt/dcdategt
lt/rdfDescriptiongt lt/rdfRDFgt
http//www.dublincore.org/documents/2000/11/dcmes-
xml/
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Example of Dublin Core Use

• A map in the United States Library of Congress
  on-line American Memory Collection

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Title

• The name given to the resourcelt META
• name DC.Title
• content Novi Belgii Novæque
• Angliænec non partis
• Virginiæ tabula multis in
• locis emendata
• lang la gt

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Creator

• An entity primarily responsible for making the
  content of the resource
• lt META
• name DC.Creator
• content Nicolaum Visscher
• gt

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Subject

• The topic of the content of the resource
• lt META
• name DC.Subject
• content Middle Atlantic States
• scheme LCSH
• gtlt META
• name DC.Subject
• content Maps
• scheme LCSH
• gtlt META
• name DC.Subject
• content Early works to 1800
• scheme LCSH
• gt

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Description

• An account of the content of the description
• lt META
• name DC.Description.Abstract
• content An historical map showing
  the coast of New Jersey as
• perceived in the seventeenth
• century
• gt

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Publisher

• An entity responsible for making the resource
  available
• lt META
• name DC.Publisher
• content Library of Congress,
• United States
• gt

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Contributor

• An entity responsible for making contributions to
  the content of the resource.
• lt META
• name DC.Contributor
• content Historic Urban Plans
• gt

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Date

• A date associated with an event in the lifecycle
  of the resource
• lt META
• name DC.Date.Created
• content 1996-04-17
• scheme W3C-DTF
• gt

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Type

• The nature or genre of the content of the
  resource
• lt META
• name DC.Type
• content imagescheme DCMIType
• gt

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Format

• The physical or digital manifestation of the
  resource
• lt META
• name DC.Format.Medium
• content image/gif
• scheme IMT
• gtlt META
• name DC.Format.Extent
• content 556K
• gt

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Identifier

• An unambiguous reference to the resource in the
  current context
• lt META
• name DC.Identifier
• content http//loc.gov/coll1/img456.jpg
• scheme URI
• gt

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Source

• A reference to a resource from which the present
  resource is derived.
• lt META
• name DC.Source
• content G3715 1685 .V5 1969 (LOC catalog )
  
• gt

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Language

• Language of the intellectual content of the
  object
• lt META
• name DC.Language
• content nlscheme ISO 639-2
• gt

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Relation

• A reference to a related resource
• lt META
• name DC.Relation.isPartOf
• content http//lcweb2.loc.gov/ammem/
• gmdhtml/dsxpimg.html
• scheme URIgt

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Coverage

• The extent or scope of the content of the
  resource
• lt META
• name DC.Coverage.Spatial
• content New Jersey
• scheme TGN"
• gtlt META name DC.Coverage.Temporal
  content 1650 scheme
  W3C-DTFgt

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Rights

• Information about rights in and over the resource
• lt META
• name DC.Rights
• content http//www.loc.gov/
• rights_statement.htm
• gt

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Distributed ContentThe Metadata Challenge

• From fixed, contained physical artifacts to
  fluid, distributed digital objects
• Need for basis of trust and authenticity in
  network environment
• Decentralization and specialization of resource
  description and need for mapping formalisms

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Multi-entity nature of object description
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Understanding Metadata based on Query Capabilities

• Simple boolean tags?
• CreatorTom Baker and Title contains Dublin
  Core
• Agent, time, place questions?
• Who was responsible for what and when and where

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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 metadata
relationships?

• 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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Content, Events, Descriptions
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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
Title Anna Karenina
Author Leo Tolstoy
Illustrator Orest Vereisky
Translator Margaret Wettlin
Date Created 1877
Date Translated 1978
Description Adultery Depression
Birthplace Moscow
Birthdate 1828
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(No Transcript)
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Queries over complex descriptive graphs

• Ability to ask questions like show me all the
  translations of War and Peace between 1980 and
  1990