Markup and Metadata

1
Markup and Metadata

• How to Build a Digital Library
• Ian H. Witten and David Bainbridge

2
Digital Library Elements

• Basic Elements of Organization
• Markup
• Controls structure and appearance
• Metadata
• Expedites access

3
Structural Markup

• Identify and maintain the document structure
• Section divisions
• Headings
• Subsection structure
• Lists
• Quotations
• Tabular information
• Structural markup items become metadata

4
Presentation Markup

• Specify how the document will appear
  typographically by formatting the document
• Page size
• Headers and footers
• Font
• Line spacing
• Section headers
• Figures

5
Kinds of Metadata

• Assist navigation
• Structural markup
• Resource discovery
• Metadata to assist in finding documents through
  searching and browsing
• Value of digital libraries depends on how easily
  information can be located
• Policy
• Define rights, restrictions, and rules that
  govern who can do what with digital resources
• Administration and Preservation
• Information necessary to preserve the integrity
  and functionality of a digital resource long term

6
Explicit versus Extracted Metadata

• Explicit Metadata
• Requires careful analysis of a document
• Takes 1-2 hours to create a traditional library
  catalog entry (or 5 minutes, depending on number
  of fields!)
• Extracted Metadata
• Text Mining
• Automatically obtained from the contents of a
  document
• Cheaper, but less reliable

7
HTML

• Hypertext Markup Language
• Document format of the World Wide Web
• Original vision separate document structure
  from presentation
• Inconsistent ways of formatting and metadata in
  HTML may discourage automatic processing of
  document collections

8
Basic HTML

• Angle brackets enclose words
• lttitlegtMy Storylt/titlegt
• Tag names are not case sensitive

9
HTML Tags

• ltpgt Paragraph
• lttrgt Table Row
• lttdgt Table Cell
• ltligt Special characters, list item
• ltimggt Images
• ltigt Italics
• ltulgt Unordered List, Bulleted List
• ltagt .. lt/agt Link Anchor

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HTML

• Opening Tags
• Attributes
• Special Markers
• Header
• Gives global information
• Title, encoding scheme, metadata
• Body
• ASCII /UTF-8 Unicode
• Local link anchors
• Navigation within a single document
• Forms
• Collect data from user
• Frames
• HTML document can be tiled into smaller,
  independent segments (each an HTML page)
• Frameset a set of frames can be displayed
  simultaneously (useful for navigation bars)

11
HTML in Digital Libraries

• Many source documents are presented in HTML form
• Explicit specification of metadata using ltmetagt
  tags
• Extract text
• Plain text browser lynx extracts text from HTML
  documents

12
XML

• Extensible Markup Language
• Flexible way to characterize document structure
  and metadata
• Well suited to digital libraries
• Widespread use

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XML Document Type Description

• DTD Document Type Description
• Tag Syntax lt!...gt
• Keywords in Block Capitals
• Square Bracket indicates DTD will appear
  in-line
• Otherwise, DTD can be in external file
• Referred to by a URL
• Desirable
• New elements
• Keyword ELEMENT
• Tag name
• Description of what element may contain
• A Leaf
• An element that is plain text, with no markup
• Declared as PCDATA (parsed character data)
• Special Characters
• Encoded as in HTML (lt amp, etc.)

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XML Regular Expressions

• Regular expression
• Comma indicates an ordered sequence
• Vertical bar indicates a choice of one element
  from sequence
• Asterisk indicates zero or more
• Plus indicates one or more
• Question mark indicates zero or one

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XML Attributes

• Attributes
• Give set of possible values
• No nesting
• Keyword ATTLIST
• Element to which it applies
• Attribute name
• Attribute type
• Appearance restrictions (optional)

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XML Entities

• Entities
• lt, amp, gt, apos, quote
• New entities can be added in the DTD
• Use syntax
• ENTITY
• Name
• value
• Example lt!ENTITY howto How to Build a Digital
  Librarygt

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XML Parameter Entity

• Several elements share the same attributes
• Parameter Entity
• Special type of entity
• Percent symbol

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Well Formed and Valid XML

• Well Formed
• A document that conforms to XML syntax but does
  not supply a DTD (Document Type Description)
• Valid
• A document that conforms to XML syntax and does
  supply a DTD
• The content follows the syntactic constraints
  defined in the DTD

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Parsing XML

• Parsing indicates whether the document conforms
  to the general rules of XML (or the specific DTD,
  when applicable)
• Parsing produces a parse tree
• Begins with a root node
• Root node has descendents
• Descendents reflect text content and nested tags
• Programming Interface
• Lets user traverse the tree and retrieve the data
• API Application Program Interface

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XML DOM

• Document Object Model
• Application Program Interface (API)
• Cross-platform
• Cross-language
• Allows programs to be written that access and
  modify the documents
• Content
• Structure
• Style

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XML and Digital Libraries

• XML is powerful
• XML allows file formats within a digital library
  to be shared
• Structure explanations are put in a DTD (Document
  Type Description)
• XML provides syntax for expressing structural
  information metadata
• XML goes further by combining with other
  standards
• Support document restructuring, querying,
  information extraction and formatting
• Can have display capabilities similar to HTML

22
Style Sheets

• Control the presentation of marked-up documents
• Two Kinds of Style Sheets
• Cascading Style Sheets
• Work with HTML and XML
• Extensible Stylesheet Language XSL
• Works with XML
• Powerful
• Allows document structure to be altered
  dynamically

23
Bibliographic Metadata

• Two Standards for Representing Document Metadata
• Machine-Readable Cataloging (MARC)
• Used by professional catalogers for use in
  libraries
• The Dublin Core
• Minimal standard used by people who are not
  trained in library cataloging
• Two metadata formats used by document authors in
  scientific and technical fields
• BibTeX
• Refer

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MARC

• Machine-Readable Cataloging
• Internally stored as collection of tagged fields
• Format covers
• Bibliographic records
• Authority records standardized forms that are
  part of the librarians controlled vocabulary
• Governed by AACR2R
• Anglo-American Cataloging Rules
• Detailed set of rules and guidelines
• Two Parts
• Part 1 Description of Documents
• Part 2 Description of Works

25
Dublin Core

• Set of metadata elements
• Simple - designed for non-specialists
• Intended for electronic materials that will not
  receive a full MARC catalog entry
• Named after Dublin, Ohio
• The first meeting was held there in 1995
• Approved by ANSI (American National Standards
  Organization) in 2001

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Dublin Core

• Fifteen metadata elements form the core element
  set
• May be refined through qualifiers
• May be augmented by additional elements for local
  purposes
• Resource
• Anything that has identity
• Similar to entity (objectives of bibliographic
  system)
• Does not impose any kind of vocabulary control or
  authority files
• Two people might generate very different
  descriptions of the same resource

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Dublin Core Metadata Standard

• Title
• Creator
• Subject
• Description
• Publisher
• Contributor
• Date
• Type

• Format
• Identifier
• Source
• Language
• Relation
• Coverage
• Rights

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BibTeX

• Manages bibliographic data and references within
  documents
• TeX
• Generalized document-processing system
• Scientific, Mathematical and Technical Purposes
• LaTeX
• Customized Version of TeX
• Freely available
• BibTeX
• Subsystem of LaTeX

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Refer

• Similar to BibTeX
• Designed by computer scientists for use by
  scientific and technical researchers
• Basis of EndNote
• Bibliographic tool which augments Microsoft Word

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Metadata for Images and Multimedia

• Metadata is not confined to text
• Most image files include data about resolution
• PNG can store text strings
• Image metadata is usually kept separate from the
  image file

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Metadata for Images and Multimedia

• Two Metadata Formats
• TIFF
• Tagged Image File Format
• Associates metadata with image files
• Widespread use for over a decade
• How images are stored in digital libraries
• Normal images
• Document images
• MPEG-7
• Multimedia Content Description Interface
• Scheme to define and store metadata associated
  with any multimedia information
• General, extensible, and still being standardized

32
Extracting Metadata

• Text Mining
• Automatic extraction of information from text
• Plain text documents
• Require text comprehension skills
• Computer techniques for text analysis
• Good results in constrained domains
• XML and other Structured Markup Languages
• Make key aspects of documents available to
  computers and people
• Encoded information can easily be extracted by
  parsing the document structure
• Few documents contain explicitly encoded metadata

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General Techniques

• Extracting Document Metadata
• Title, Author, Publisher, Date, etc.
• Generic Entities
• Email, URLs, Dates, Time, Money
• Bibliography Entries
• Citation analysis

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Key Phrase Metadata

• Key-phrase metadata can successfully be obtained
  automatically from documents
• Two Different Approaches
• Key-Phrase Assignment
• Key-Phrase Extraction

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Generating Phrase Hierarchies

• Key phrases consist of a few well-chosen words
  that characterize the document
• It is useful to extract a structure that contains
  ALL the phrases in the documents
• Hierarchical structure of phrases can support
  browsing around a digital library collection