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Metadata Michael J. Watts mike.watts.nz

Metadata Michael J. Watts http://mike.watts.net.nz. Lecture Outline. What is metadata? The need for metadata XML Metadata and XML Problems with XML. What is metadata?. Data about data Documentation about data Describes a set of data Source Dimensions Variables. What is metadata?.

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Metadata Michael J. Watts mike.watts.nz

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  1. Metadata Michael J. Watts http://mike.watts.net.nz

  2. Lecture Outline • What is metadata? • The need for metadata • XML • Metadata and XML • Problems with XML

  3. What is metadata? • Data about data • Documentation about data • Describes a set of data • Source • Dimensions • Variables

  4. What is metadata? • Describes an object • Owner • Location • Metadata has structure • Metadata can describe structure • Database schema

  5. The Need for metadata • Sufficiency • Can an object describe itself? • e.g., images • Scalability • Allows for rapid searching • Searching metadata fields vs large data files • Interoperability • Can exchange data using mutually agreed metadata formats

  6. XML • Extensible Markup Language • Uses tags to describe data elements • A standard defined by the W3C • Standard for data exchange over networks • Few predefined elements • Minimalist • A tree structure • Parent nodes, subnodes

  7. XML • Example XML document <address> <name> <title>Mr.</title> <firstname>John</firstname> <lastname>Smith</lastname> </name> <street-address>1000 Main Street</street-address> <city>Los Alamitos</city> <state>CA</state> <zip>90720</zip> </address> - Steven J. Vaughan-Nichols, “XML Raises Concerns as it Gains Prominence”, IEEE Computer, May 2003, pg14-16

  8. XML • Elements in XML described by a DTD • Document Type Definition • Describes elements • Name • Type • Format • Order

  9. XML • XML document is Well-formed if • Element tags are matched • The tags are closed correctly • XML document is Valid if • Structure conforms to the DTD

  10. Metadata and XML • The elements in an XML document describe the data • Elements are metadata • Grammar in the DTD describe the elements • Metadata for the elements • The flexibility of XML illustrates the use of metadata

  11. Problems with XML • Large files • Tags add bulk • Addressed with compression • Security • Files are plain text • Addressed with encryption

  12. Summary • Metadata is data about data • Needed to help with • describing data sets • searching for data • communicating data • XML is a metadata format • XML widely used to transfer data between systems

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