Dublin Core Metadata Tutorial July 9, 2007 Stuart Weibel Senior 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 Metadata §The Web as an information system §The Internet Commons §Interoperability is key §MARC lives §The varieties of metadata §Modularity §Some 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 Home Pages Scientific Data Commerce Geo Library Internet Commons Museums Whatever. . .
Interoperability requires 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-AACR 2 cataloging • MARC is the communications format • AACR 2 (Anglo-American Cataloging Rules) defines the cataloging rules (semantics § MARC and AACR 2 are evolving • Closer alignment with XML as a syntax option • RDA is an effort to modernize AACR 2, 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
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 money A 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/october 00/baker/10 baker. 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 property resource statement value • More about the Dublin Core Abstract model later
What are the properties and values in the following metadata statements? 245 00 $a Amores perros $h [videorecording] <title> Nueve reinas </title> <type> Moving. Image </type> • Different models for conveying related information • Dublin Core syntax fits in more naturally with the structure of the Web
implied verb implied subject Resource has one of 15 properties property value (an appropriate literal) DC: Creator DC: Title DC: Subject DC: Date. . . property [o pti [o on al X pti on qu ali al qu a fie lifie r] r] qualifiers (adjectives)
The fifteen elements (properties)
Varieties of qualifiers: Element Refinements § Make the meaning of an element narrower or more specific. • a Date Created versus a Date Modified • an Is. Replaced. By 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 Subject "Languages -- Grammar" LC SH Resource has Date IS O 8 Rev 60 ise d 1 "2000 -06 -13"
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 “Verfasser” label dc: creator [Server in Germany]](https://present5.com/presentation/bd571e05847cb93c93b7bf4a9bf57120/image-35.jpg "One token – labels in many languages “Verfasser” label dc: creator [Server in Germany]")
One token – labels in many languages “Verfasser” label dc: creator [Server in Germany] label “Creator” [DCMI Server] label [Server in “Pencipta” Jakarta]
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 Model §Terminology Simple versus Qualified DC Resources Description sets Value Strings Element refinements Encoding Schemes §Graphical representation of the Abstract Model §Summary of general ideas
Important DCMI Document concerning the 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: property resource statement value
What is a resource? § W 3 C 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 DCMI TYPE Vocabulary Collection Dataset Event Image Interactive Resource Moving Image Physical Object Service Software Sound Still Image Text
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 subproperties § 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 book Illustrator 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 LCSH 616. 02774 is a value from DDC-22 • A syntax encoding scheme is used to indicate the structure of a value string 2004 -10 -12 is structured according to the W 3 CDTF 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
Abstract Model summary (after Andy Powell) Record (encoded as html, XML, or RDF/XML Description set Resource Description (URI) Vocabulary Statement encoding scheme Statement property (URI) value URI value string syntax encoding scheme language (pt-BR)
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 Alternatives HTML… 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. W 3 CDTF" 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 Terms http: //dublincore. org/documents/dcmi-terms/ § The namespaces are a result of historical developments • DC: [original elements] • DCTERMS: [later elements]
Syntax Alternatives: XML § XML = e. Xtensible 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 datatype 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-PMH OAI Protocol for Metadata Harvesting § Open Archives Initiative http: //www. openarchives. org • Simple Protocol for sharing metadata records § Based on HTTP, 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 § W 3 C 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 § W 3 C – Resource Description Framework (RDF) http: //www. w 3. org/RDF/
Summary: Syntax alternatives § Choices should be driven by local requirements and objectives • Available expertise • Costs of Deployment • Objectives and functional requirements
Association Models Where 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 Core and 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, 6 UK DC 2 Australia DC 4 Finland DC 5 Germany DC 7 Canada DC 8 § Conferences Tokyo (2001) Florence (2002) Seattle (2003) China (2004) Spain (2005) 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 2413. txt § CEN Workshop Agreement (Europe) • endorse Dublin Core elements as CWA 13874 § NISO Z 39. 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. Weibel Visit me at: http: //weibel-lines. typepad. com Contact me at: Weibel@oclc. org Thank you for your attention
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