Lifecycle Metadata for Digital Objects

1. Lifecycle Metadata for Digital Objects September 27, 2004 Implementing Metadata in XML

2. What constitutes the XML environment? • XML editor (note that it can’t 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)

3. Tools for home use • In class we will be using XMetaL Author, but it’s not free (there is a trial download if you are a registered Corel user). • One free XML authoring environment is Amaya from the W3C: http://www.w3.org/Amaya/ • Another is XML Cooktop: http://www.xmlcooktop.com/ • You can also validate individual XML files using online web services pointed to at: http://www.cogsci.ed.ac.uk/~richard/xml-check.html

4. 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)

5. XML does nothing • XML structures information • XML stores information • XML sends information • XML is not procedural

6. 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

7. 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 doesn’t suit everything; “overlap” problem)

8. Why mark up the object itself? • 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

9. Best of both worlds • XML metadata tags • (Text) object marked up in XML • Original (text) object pointed to in separate file for preservation

10. XML Syntax rules for well-formed XML • An element containing text or elements must have start and end tags • An empty element’s tag must have a slash (/) before the end bracket • 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, and case is significant

11. *Structure of the XML Document* • Document prologue • XML declaration • Document type declaration • Points to root element • Points to external standards (DTDs, namespaces) • Lists special internally-defined elements • Document itself • Bracketed by root element • Contains elements, attributes, entities • Nested structure

12. XML Declaration • Gives version of XML • <?xml version=“1.0”?> • Defines character encoding • <?xml version=“1.0” encoding=“UTF-8”?> • Indicates presence of other needed files • <?xml version=“1.0” encoding=“UTF-8” standalone=“no”?>

13. Document type declaration • Points first to root element • <!DOCTYPE example> • Then points to any external source for definition of document structure • <!DOCTYPE example SYSTEM “c:\My Documents\classes\metadata\example.dtd”…> • Then adds any overriding local elements (internal subset)

14. 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: it is 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)

15. Element declarations in the DTD • Occur within the DTD or to give local definition overriding the DTD • <!ELEMENT name content-model> • Content-models: • (#PCDATA) for character data • (element, element, element…) modified by , | ? + *

16. Attribute declarations in the DTD • All attributes for one element declared in an attribute list • Gives attribute name, attribute’s data type, attribute’s behavior • <!ATTLIST elementname attname1 atttype1 attdesc1 attname2 atttype2 attdesc2 >

17. Entity declarations in the DTD • General entities are like variables. They assign a name and define a type. Examples: • quoted text <!ENTITY title “Temporary crazy title”> • text from an external source • other data from an external source <!ENTITY logo SYSTEM “images/logo.gif” NDATA gif>

18. Elements in the XML document • Container elements (element tags bracket data) • <name attribute=value>chardata</name> • Empty elements (no data is contained, begin and end element tags are collapsed to one) • <name attribute=value />

19. Attributes in the XML document • Used to provide more details about an element • <elementname attname=“value”>

20. Entities in the XML document • The “entity” behaves like a “variable” • Within the document, the entity name is used preceded by an ampersand: • <greeting> Dear &name, </greeting> • When the document is displayed or used, the entity value at the time will be substituted for the name

21. 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

22. XML Cooktop editor screenshot

23. Amaya screenshot

24. 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