Dublin Core Metadata Tutorial

July 9, 2007

Stuart WeibelSenior Research Scientist

OCLC Programs and Research

Tutorial Roadmap

Principles of Metadata Dublin Core Metadata Basics The Dublin Core Abstract Model Syntax Alternatives for DC Metadata Mixing and Matching Metadata History and workings of the Dublin Core Metadata

Initiative

Acknowledgements: I have borrowed liberally from tutorial slides sets from Tom Baker, Diane Hillman, Andy Powell, and Marty Kurth, available at Dublincore.org

Basic Principles of MetadataThe Web as an information systemThe Internet CommonsInteroperability is keyMARC livesThe varieties of metadataModularitySome Challenges

State of the Web as an Information System

Search systems are motivated by business models, not functionality

Index coverage is broad, but unpredictable Too much recall, too little precision Index spam abounds Resources (and their names) are volatile What about versions, editions, back issues? Archiving is presently unsolved Authority and quality of service are spotty Managing Intellectual Property Rights is difficult

Metadata: Part of a Solution

Structured data about other data• helps to impose order on chaos• enables automated discovery/manipulation

Full Text Web indexing is the dominant idiom for search

Metadata is more useful in structured collections, used in combination with applications designed to take advantage of structured descriptions

Internet Commons includes Multiple Communities

ScientificData

HomePages Geo

InternetCommons

Library

Museums

Commerce

Whatever...

Interoperabilityrequires conventions about:

Semantics• The meaning of the elements

Structure• human-readable• machine-parseable

Syntax• grammars to convey semantics and

structure

Haven’t we done metadata already?

The MARC family of standards is the single most successful

resource description standard in the world

MARC Cataloging…

Is really MARC-AACR2 cataloging• MARC is the communications format • AACR2 (Anglo-American Cataloging Rules)

defines the cataloging rules (semantics MARC and AACR2 are evolving

• Closer alignment with XML as a syntax option• RDA is an effort to modernize AACR2, and

alignment it with networked environments RDA and Dublin Core are cooperating on

alignment of a common underlying data model.

What’s wrong with this model on the Web? Expensive

• Complex • Professional Catalogers required

Bias towards bibliographic artifacts• Fixed resources• Incomplete handling of resource evolution and

other resource relationships Anglo-centric

• MARC 21 accounts for ¾ of MARC records, but there are many other varieties

Metadata Takes Many Forms

resourcediscovery

documentadministration

rightsmanagement

contentrating

security andauthentication

archivalstatus

products andservices

databaseschemas

process controlor description

Warwick Framework: Modular Metadata

Conceptual Architecture for metadata from the Warwick Metadata Workshop (DC-2)

Conceptual architecture to support the specification, collection, encoding, and exchange of modular metadata

Provide context for metadata efforts (including Dublin Core)• avoids the “black-hole” of comprehensive

element sets• focuses interoperability issues at package level

A conceptual framework, NOT an application

Modularity and Extensibility: the Lego metaphor DC is a beginning, not an end An architecture for modular, extensible

metadata The simplest common denominator

• Add stuff you need for• Local requirements• Domain specific functionality• Other dimensions of description

• Eg cloud cover… management… structural metadata….

Descriptive Metadata Standards

IEEE LOM (Learning Object Metadata)• Descriptive and structural metadata to support

instructional systems ONIX (Online Information Exchange) – bookseller metadata FGDC – Federal Geographic Data Committee: rich

descriptive and structural metadata for GIS applications Encoded Archival Description – description of archival

collections MPEG Multimedia Metadata – large, complicated, still in

progress – descriptive, structural, rights management Dublin Core – core descriptive metadata

Metadata Creation

Metadata is expensive and error prone• A MARC Record costs about $100 USD to create

one record at the Library of Congress• Competes with indexing at… $ 00.001 ???

Capture it as close to point of creation as possible Capture as much automatically as possible Should be designed with close attention to the

functional requirements it serves Re-use existing standards whenever possible Always tension between completeness of

description, intended purpose, and cost

Metadata Challenges Accommodate multiple varieties of metadata

Tension: functionality and simplicity

Tension: extensibility and interoperability

Human and machine creation and use

Community-specific functionality, creation, administration, access work at cross purposes to global interoperability

Interoperability barriers cost time and moneyA Common data model helps avoid this

Dublin Core Basics

Design Philosophy – useful metaphors Language and pidgins Characteristics of DC metadata The simple bucket (properties) Resource Types Metadata grammar Dublin Core Principles One-to-one Dumb-down rule Context appropriate values Translations

Dublin Core: Starting Assumptions and Essential Features Simple

• true to a point: the elements are simple, the underlying model is not

Consensus-based• Crucial to early success, both in attracting

expertise and deployment. Bottom up Based on the experience of practitioners, but

hard to capture and capitalize on lessons learned Cross-disciplinary and International

• Central success factor

Essential Features (continued) The Web is the strategic application

• On the mark International

• Also central success factor, but hard (20 languages in the Registry)

Lego-like modularity & extensibility• Partially realized promise• Application Profiles are the means

Syntax independence• An ongoing nightmare (HTML…XML…RDF/XML)

Authors will describe their own works• Laughably naïve

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 Internet.

A Grammar of Dublin Core

By design not as rich as mother tongues, but easy to learn and 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...

http://www.dlib.org/dlib/october00/baker/10baker.html

Basic Structures in Dublin Core Metadata

The basic unit of metadata is a statement:• Statements consist of a property (a metadata element)

and a value• Metadata statements describe resources

• More about the Dublin Core Abstract model later

resource statement

value

property

What are the properties and values in the following metadata statements?

245 00 $a Amores perros $h [videorecording]

<title> Nueve reinas </title>

<type> MovingImage </type>

• Different models for conveying related information

• Dublin Core syntax fits in more naturally with the structure of the Web

Resource has property

DC:CreatorDC:TitleDC:SubjectDC:Date...

X

implied subject

impliedverb

one of 15properties

property value(an appropriateliteral)

[optional qualifier]

[optional qualifier]

qualifiers(adjectives)

The fifteen elements (properties)

Creator Title SubjectContributor Date Description

Publisher Type Format

Coverage Rights Relation

Source Language I dentifier

Varieties of qualifiers:Element Refinements

Make the meaning of an element narrower or more specific.• a Date Created versus a Date Modified• an IsReplacedBy Relation versus a Replaces

Relation

If your software does not understand the qualifier, you can safely ignore it.

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.

Resource has Date "2000-06-13"Revised

ISO8601

Resource has Subject "Languages -- Grammar"LCSH

Dumb-Down Principle for Qualifiers

Simple DC does not use element refinements or encoding schemes – statements contain only value strings

Qualified DC uses features of the DCMI Abstract Model, including element refinements and encoding schemes

Dumbing-down is translating Qualified DC to simple DC

Qualifiers refine meaning (but may be harder to understand)

The One to One Principle

Each resource should have one metadata description• For example, do not describe a digital image of

the Mona Lisa as if it were the original painting

Group Related descriptions into description sets• Describe an artist and his or her work

separately, not in a single description

Appropriate Values

There are generally tradeoffs between local requirements and global requirements

Use elements and qualifiers to meet the needs of your local context, but…

Keep in mind that machines and people use and interpret metadata, so…

Consider whether the values used will help discovery outside your local context

Dublin Core as a multilingual metadata language

Dublin Core has been translated into 20 + languages• machine-readable tokens are shared by all• human-readable labels are defined in different

languages• translations are distributed, maintained in

many countries• eventually linked in DCMI registry

One token – labels in many languages

dc:creator“Verfasser”label

“Creator”label

“Pencipta”

label

[Server inGermany]

[Server inJakarta]

[DCMI Server]

Metadata languages are "multilingual"

Metadata is not a spoken language The words of metadata -- "elements" -- are

symbols that stand for concepts expressible in multiple natural languages

Standards may have dozens of translations

Are concepts like "title", "author", or "subject" used the same way in English, Finnish, and Korean?

DCMI Open Metadata Registry

Managing vocabularies defined by the DCMI• Languages• Versioning• Controlled vocabularies

Foundation for modular, incremental integration and evolution

The Registry working group is a Dublin Core Community with participants around the world

The Dublin Core Abstract ModelTerminology Simple versus Qualified DC Resources Descriptions Description sets Value Strings Element refinements Encoding SchemesGraphical representation of the Abstract ModelSummary of general ideas

Important DCMI Document concerningthe Abstract Model and Syntax alternatives DCMI Abstract Model http://dublincore.org/documents/abstract-model/

Expressing Dublin Core in HTML/XHTML meta and link elements

http://dublincore.org/documents/dcq-html/

Expressing Dublin Core metadata using the Resource Description Framework (RDF)

http://dublincore.org/documents/dc-rdf/

Expressing Dublin Core metadata using XML http://dublincore.org/documents/dc-xml/

Simple versus Qualified DC

Simple DC supports single descriptions using the 15 base elements and value strings

Qualified DC supports the richer features of the Abstract Model, and allows the use of all DCMI terms as well as other, non-DCMI terms.

An application profile is used to specify a metadata application that includes DCMI terms in combination with non-DCMI terms (mix & match metadata).

The DCMI Abstract Model

A data model for Dublin Core Agreed upon underlying structure for metadata

statements Many years in the making -- long term contention Describes the structure of statements about

resources that we make in our metadata language:

resource statement

value

property

What is a resource? W3C definition:

• “anything that has identity… electronic document, an image, a service”

• “not all resources are network retrievable; e.g. human beings, corporations, and bound books can also be considered resources”

In other words, a resource is anything we can identify:• Physical things (books, people, airplanes….)• Digital things (Images, web pages, services….)• Concepts (colors, subjects, eras, places)

In the DC context, the DCMI Type list describes the stuff we describe with DC metadata

Resource types for which DC is often used

Collection Dataset Event

Image InteractiveResource

Moving Image

Physical Object

Service Software

Sound Still Image

Text

DCMI TYPE Vocabulary

Abstract Model: Descriptions

A description is composed of:• One or more statements about a single

resource• Optionally, the URI of the resource being

described

Each statement is made up of • A property URI (that identifies a property)• A value URI (that identifies a value) and/or one

or more representations of the value (a value string)

Terminology: Value Strings

A value string is a human-readable string that represents the value of the property

Each value string may have an associated value string language that is an ISO language tag (e.g., pt-BR)

Terminology: Element Refinements

Elements are the same as properties Element refinements are the same as sub-

properties An element refinement is a special case of an

element that shares the meaning of its ‘parent’, but has narrower semantics

Paulo is illustrator of a book, therefore he is also a contributor to the bookIllustrator is an element refinement of

contributor

Terminology: Encoding Schemes Values and value strings can be ‘qualified’ by

encoding schemes in order to clarify their meaning• A Vocabulary Encoding Scheme is used to

indicate a terminology set from which a value is taken:Stem cells—Research is a value from LCSH616.02774 is a value from DDC-22

• A syntax encoding scheme is used to indicate the structure of a value string2004-10-12 is structured according to the

W3CDTF rules for date encoding

Terminology: Description Sets

The 1:1 principle dictates that each description describes one, and only one, resource

We often need to describe grouped sets of descriptions, which are known in the abstract model as description sets• An article and its authors• A painting and its artist

When description sets are exchanged between software applications, they are generally encoded according to a particular syntax in a metadata record

Record (encoded as html, XML, or RDF/XMLDescription set

Resource Description (URI)Resource Description (URI)Resource Description (URI)

Statement

Statement

Statement

language

(pt-BR)

Abstract Model summary (after Andy Powell)

value string

value URIproperty (URI)

syntax encodingscheme

Vocabulary encoding scheme

General Ideas

DC is not just the 15 elements, though they comprise the foundation for simple DC

50+ properties (elements) have been approved by DCMI

The model supports local declarations of additional properties

The model supports application profiles (mixing DC elements with those of other sets)

The model allows the grouping of descriptions to create more complex description entities

Syntax Alternatives Choosing among alternatives HTML XML RDF/XML

Syntax AlternativesHTML… XML… RDF/XML

Three Web-based models for deploying metadata Each has advantages and disadvantages What is ‘best’ depends on local constraints

• What is the objective of the system? How do these syntax alternatives support local functional requirements?

• Are there services and software to ‘consume’ the metadata created?

• Are trained practitioners available to create and support the systems?

Syntax Alternatives: HTML Advantages:

• Simple – META tags embedded in content• Widely deployed tools and knowledge• Resource carries its metadata around with it• Metadata is openly harvestable

Syntax Alternatives: HTML (continued)

Disadvantages• Limited structural richness (does not support

hierarchical, tree-structured data• Management of metadata is less reliable (the

metadata is out in the wild)

Describe one thing (the HTML document) and no more!

Dublin Core in HTML (example)

<head><link rel="schema.DC" href="http://purl.org/dc"> <meta name="DC.title"

content=“DC Metadata Tutorial”<meta name="DC.creator"

content=“Stuart L. Weibel"> <meta name="DC.subject" xml:lang= “en-US’

content=“Metadata"> <meta name="DC.date" scheme=“DCTERMS.W3CDTF"

content=“2007-07-08"><meta name=“DCTERMS.audience”

content =“technical librarians”</head><body>… [ rest of html document ]

The namespaces for HTML encoding

All DCMI terms (elements, element refinements, and encoding schemes) are found in:

DCMI Metadata Termshttp://dublincore.org/documents/dcmi-terms/

The namespaces are a result of historical developments• DC: [original elements]• DCTERMS: [later elements]

Syntax Alternatives: XML

XML = eXtensible Markup Language The standard for networked text and data Wide-spread tool support

• Parsers are widely available • Extensibility (XML namespaces) • Type definitions (XML Schema)• Transformation and Rendering (XSLT)• Rich linking semantics (XLINK)

XML Schema

Rich XML-based language for expressing data-type semantics

Replaces arcane and limited DTD (origin in SGML) Facilities:

• Data typing (both complex and primitive)• Constraints (ranges, cardinality…)• Defaults (specify defaults for certain

properties)

Dublin Core fragment in XML

<metadata xmlns:dc="http://www.openarchives.org/OAI/dc.xsd">   <dc:creator>Carl Lagoze</dc:creator> <dc:title>Accommodating Simplicity and Complexity in Metadata</dc:title> <dc:date>2000-07-01</dc:date>       <dc:publisher>Cornell University, Computer Science</dc:publisher></metadata>

Where is the rest of the stuff? In the schema!   

Case Study: OAI-PMHOAI Protocol for Metadata Harvesting Open Archives Initiative

http://www.openarchives.org

• Simple Protocol for sharing metadata records Based on HTTP, XML, XML Schema, and XML

namespaces Allows a harvester to query a remote repository

for some or all of its metadata records DC is the default native metadata format in the

OAI protocol

Syntax Alternatives: RDF

RDF (Resource Description Format) Syntax expressed in XML W3C recommendation for encoding metadata (a

semantic Web technology) Enabling technology for richly-structured metadata Rich data model (the DC Abstract Model is a

constrained version of RDF) Metadata can be shared easily among independent

applications that understand RDF W3C – Resource Description Framework (RDF)

http://www.w3.org/RDF/

Summary: Syntax alternatives

Choices should be driven by local requirements and objectives• Available expertise• Costs of Deployment • Objectives and functional requirements

Association ModelsWhere do we keep the metadata? Embedded

• HTML META tags or XML or RDF-XML can be embedded in the resource, and hence travels with the resource

• Simple, but limited in structural richness Loosely coupled

• Shadow Files (like Adobe’s XMP Sidecar files)• Requires a system to manage and insure that they stay

in synch• RDF or XML descriptions

Third Party Metadata• Stored in repositories such as library catalogs• Easier to manage and maintain, and provide service• Library catalogs, for example

Questions about syntax alternatives?

Application Profiles:Mixing and Matching Metadata

What is an Application Profile? Why bother? Creating new properties Documenting and declaring new properties Some examples

Application Profiles: Mixing and Matching Metadata• The mixing and matching of elements (properties)

from separate metadata sets• An expression of metadata modularity• Implementers can benefit from peer applications• Communities can harmonize their metadata,

picking complementary properties• Promotes convergence over time• For application profiles to work, there must be

public declarations of properties that conform to a common data model (or nearly so)

Application Profile: Definition

Declaration of metadata properties used in a given organization or application or community

Documentation of encodings, constraints, and creation guidelines

Implies formal schemas (xml schemas or RDF schemas)

Should promote both human understanding and machine interoperability

The concept of application profiles applies to any metadata community of practice, not just DC

DC has promoted their use and leads by example

Why bother?

One-size-fits-all metadata results in bloated, unmanageable specifications and applications

APs allow tailoring a given metadata application to match the element set to specific functional requirements based on local or community needs, while retaining interoperability with a larger metadata community

Creating an Application Profile

Find out what others have done… don’t re-invent wheels!

Develop community consensus Define Name, Label, definition relationships (see

the DCMI Usage Board guidelines) Determine an appropriate URI (a home on the

Web)

Dublin Core Application Profile Guidelines http://dublincore.org/usage/documents/profile-guidelines/

Document New Properties

At very least: a Web page with relevant information

Better: a web page with a public schema using new terms in an application profile

Better still: all properties available as part of a metadata registry

Example Application Profiles

DC-Library AP

DC-Collection Description AP

DC-Government AP

DC-Education AP

Some History of the Dublin Coreand

How the Initiative Works

• The Beginnings • Landmarks• Workshops and Conference series• What the initiative does• Standardization• Some example applications

Dublin Core: The Beginning

A casual discussion at WWW-2 in Chicago, October of 1994• How to make things on the Web easier to find?

OCLC & NCSA co-sponsored an invitational workshop in March of 1995

The workshop became a workshop series, and eventually a conference series

DCMI: Dublin Core Metadata Initiative• Governance and process evolved over time• De facto standards maintenance body

Dublin Core Landmarks

1994: Simple tags to describe Web pages 1995: The Dublin Core is one of many

vocabularies needed ("Warwick Framework")

1996: The Dublin Core: 13 elements expanded to 15 - appropriate for Text and Images

1997: WF needs formal expression in a Resource Description Framework (RDF)

Dublin Core Landmarks (continued)

2000: Dublin Core Metadata Initiative recommends qualifiers, broadens its organizational scope beyond the Core

2001: Workshop Series becomes a conference series

DCMI Affiliates and a board of trustees 2005: Abstract Model (Finally)

The Dublin Core Workshop Series Workshop Venues:

US DC 1, 3, 6UK DC 2Australia DC 4Finland DC 5Germany DC 7Canada DC 8

ConferencesTokyo (2001) China (2004)Florence (2002) Spain (2005)Seattle (2003) Mexico (2006)

DCMI Activities

Standards development and maintenance Metadata registry and infrastructure Technical working groups and periodic

workshops Tutorial materials and user guides Education and training Open source software Liaisons with other standards or user

communities

Governance of DCMI

DCMI has a Board of Trustees that oversees the operation and goals of the initiative

Managing Director• Makx Dekkers

Director of Specifications and Documentation• Tom Baker

An Advisory Board of metadata experts provides guidance on metadata issues

The DCMI Usage Board

The Usage Board is an editorial committee that evaluates proposals for new elements or revisions

International selection of metadata experts Meet twice yearly Documents decisions and updates DCTERMS

document

Affiliate Program

DCMI has National Affiliates which support the Initiative and are represented on the Board of Trustees• Finland• UK• Singapore• New Zealand• Korea

OCLC has been the Host from the start

The Three I’s

Independent: DCMI is not controlled by specific commercial or other interests and is not biased towards specific domains nor does it mandate specific technical solutions

International: DCMI encourages participation from organizations anywhere in the world, respecting linguistic and cultural differences

Influenceable: DCMI is an open organization aiming at building consensus among the participating organizations; there are no prerequisites for participation

The Work gets done by Communities and task groups Accessibility Community Collection Description Community Education Community Environment Community Global Corporate Circle Government Community Kernel Community Libraries Community Localization and Internationalization Community Preservation Community Registry Community Social Tagging Community Standards Community Tools Community

Standardization of the Dublin Core

IETF RFC 2413• http://www.ietf.org/rfc/rfc2413.txt

CEN Workshop Agreement (Europe)• endorse Dublin Core elements as

CWA13874 NISO Z39.85

• National Information Standards Organization, an ANSI affiliate

ISO 15836

Metadata Applications - examples Governments

• 7 governments have adopted DC metadata• Adobe products

• XMP – Adobe’s variant of RDF• Dublin Core is a base schema

IPTC – International Press and Telecommunications Council• Dublin Core based standard for journalism

Knowledge Management systems commonly use DC metadata

Visual materials require metadata for findability Library Systems (mostly MARC cataloging, but

increasingly other metadata as well)

Metadata applications (continued)

Search Systems• Full text indexing is enormously useful• Structured metadata improves search• The Amazoogles are all aggressively courting

metadata aggregators Cameras

• Automatically create metadata for each image• Some even include GPS data

Commerce systems require metadata Social Software applications are largely about enriching

resource information with tags, reviews, and automated linking

To Sum Up…

Many purpose-built metadata standards Few have explicit data models Few interoperate Some will survive, others will not The Web demands convergence

• Break down silos between domains and communities of practice

• RDF should help promote convergence, but we are not there yet

Expect more metadata standards, but hope for fewer

How to Participate

Join the DC-General mailing list

Join a working group

Information on lists and working groups is available at http://dublincore.org

Stuart L. WeibelVisit me at: http://weibel-lines.typepad.comContact me at: Weibel@oclc.org

Thank you for your attention