URC Simplification

by Daniel LaLiberte, NCSA

NCSA

For more information, see "A simplification of URN and URC issues".

URC == Metadata == Data

• What's the difference between a description OF a thing and the thing ITSELF?
• What is "About" about?
• Metadata - the Never-Ending Story. Metadata or Data?
  • A Collection of Alternative Representations
  • A Collection of Component Parts
  • A Collection of Replicas
  • A Collection of Abstracts
  • A Table of Contents
  • Type, size, format of the data
• How distantly related, and still in the family?
• Do we avoid these questions or face them HEAD on?

Metadata != Data

• One difference remains: Metadata is just not the Data
• Client may request data or metadata.
• Server(s) can return data or metadata.
• Metadata may be directly identified by its own URI, or indirectly identified as a method on the data.
• Object Oriented Perspective:
  • Behavior of object (i.e. Data) is the real issue
  • Not its Representation
  • Not its Location
  • Not its Meta-ness

Clean Separation between URCs and URNs

• URCs should not depend on URNs, even if they were defined.
• URNs should not depend on URCs, even if they were defined.
• URIs are OK - generic identifiers, no specific properties.
• Does resolution of URN always return URC? No!
• Does resolution of URL sometimes returns URC? Yes!
• HTTP extension? - header to indicate "This is metadata".

URC is General Data Structure

• Set of name-value pairs
• Embedded and Referenced values
• Primitive and Structured values
• Ordered list of values
• Data Inheritance and Type Inheritance
• Self-describing