Lifecycle Metadata for Digital Objects

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Lifecycle Metadata for Digital Objects

• September 18, 2002
• Implementing Metadata in XML

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Review of orders of data

• First-order language (segmentation)
• Second-order encoding
• Third-order meaning
• Fourth order function
• Fifth order groups of 3 and/or 4
• Note that each order is meta with respect to
  the one below and data with respect to the one
  above (cf. Goedel)
• Hence you mark up the order you wish to
  objectivize and access (examples TEI, EAD)

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Two fancy wrappers (what orders are involved?)

• The XML document as metadata repository
• XML document contains all the metadata
• Objects themselves are in separate files pointed
  to by the document (XLinks)
• The XML document as the whole enchilada
• Object is marked up in XML too
• Metadata is added as additional elements to the
  original object

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Why not mark up the object (I.e., place markup
within the object)?

• If the object is not a text!
• If the object is a text, but the text is too
  complex to mark up in XML (hierarchical model
  doesnt suit everything overlap problem)

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Why mark up the object?

• If the object is a text
• If the text is well-formed as a hierarchical
  structure (problem of overlaps not solved in XML)
• Advantage is that the object carries its own
  metadata

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Best of both worlds

• XML metadata tags
• (Text) object marked up in XML
• Original (text) object pointed to in separate
  file for preservation

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XML Syntax rules for well-formed XML

• An element containing text or elements must have
  start and end tags
• An empty elements tag must have a slash (/)
  before the end bracket
• Case is significant
• All attribute values must be in quotes
• Elements may not overlap
• Isolated markup characters may not appear in
  parsed content
• Element names may not use all characters

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What constitutes the XML environment?

• XML editor (note that it cant do anything
  automatic until you load a DTD or schema or have
  entered a number of elements)
• XML parser/validator
• Display program (e.g. browser)
• DTD or schema to define elements
• Style sheet for display of elements
• XSLT engine to convert to other formats (e.g.
  database)

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The XML Document

• Document prologue
• XML declaration
• Document type declaration
• Points to root element
• Points to external standards (DTDs, namespaces)
• Document itself
• Bracketed by root element
• Contains elements, attributes, entities

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XML Declaration

• Gives version of XML
• lt?xml version1.0?gt
• Defines character encoding
• lt?xml version1.0 encodingUTF-8?gt
• Indicates presence of other needed files
• lt?xml version1.0 encodingUTF-8
  standaloneno?gt

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Document type declaration

• Points first to root element
• lt!DOCTYPE examplegt
• Then points to any external source for definition
  of document structure
• lt!DOCTYPE example SYSTEM c\My
  Documents\classes\metadata\example.dtd
• Then adds any overriding elements (internal
  subset)

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Function of the DTD

• Document Type Definition not expressed in XML
• Defines the language in which you will be talking
  about objects and against which the XML markup
  may be validated the grammar of the XML document
  that refers to it
• Equivalent to declaration of data types in a
  programming language allows you to define your
  own types (a private, or SYSTEM DTD)
• Or you can use a preexisting DTD (a PUBLIC DTD,
  example EAD)

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Element declarations in the DTD

• Occur within DTD or to give local definition
  overriding DTD
• lt!ELEMENT name content-modelgt
• Content-models
• (PCDATA) for character data
• (element, element, element) modified by
• , ?

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Attribute declarations in the DTD

• All attributes for one element declared in
  attribute list
• Gives attribute name, attributes datatype,
  attributes behavior
• lt!ATTLIST elementname
• attname1 atttype1 attdesc1
• attname2 atttype2 attdesc2
• gt

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Entity declarations in the DTD

• General entities are like variables they assign
  a name and define a type for quoted text text
  from an external source other data from an
  external sourcelt!ENTITY title Temporary crazy
  titlegtlt!ENTITY logo SYSTEM images/logo.gif
  NDATA gifgt

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Elements in XML document

• Container elements
• ltname attributevaluegtchardatalt/namegt
• Empty elements
• ltname attributevalue /gt

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Attributes in XML document

• Used to provide more details about an element
• ltelementname attnamevaluegt

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Entities in XML document

• Within the document, the entity name is used
  preceded by an ampersand
• ltgreetinggt Dear name, lt/greetinggt
• When the document is displayed or used, the
  entity value will be substituted for the name

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Tools for working with XML

• Authoring, display
• Amaya (free W3C browser/authoring software)
• XML Cooktop (free XML authoring software)
• Display
• Internet Explorer
• Netscape 6
• Mozilla
• Database
• Apache Xindice

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XML Cooktop editor screenshot
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Amaya screenshot
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How does all this relate to databases?

• By defining a language for markup in XML, you
  create categories
• Even freely-occurring objects can thus be found
  and grouped (e.g., TEI grammatical markup)
• Compare to accepted method of placing text in a
  relational table in order to process it
• Especially useful for regularly-occurring
  metadata
• This is why the structure of a markup scheme is
  so important you get what you pay for