Metadata that record when a cache copy was retrieved, the identifiers (etags) of that copy and possibly also other data. It is used to guide cache coherence policies and cache management in general.

Item Summary
Name	Type	Multiplicity	Description
retrievalTimestamp	property dateTime	[0,1]	The timestamp of a time moment when the object was retrieved from the source.
serialNumber	property string	[1,1]	A string that uniquely represents the version of the data that was retrieved.

Items
- retrievalTimestamp
  
  Flags: RAM,runtime
  
  Multiplicity: [0,1]
  
  The timestamp of a time moment when the object was retrieved from the source. Used mostly for diagnostics and general visibility. As this is relatively rough granularity and the time in distributed system is relative anyway, it is not really useful for anything else.
- serialNumber
  
  Flags: RAM,runtime
  
  Multiplicity: [1,1]
  
  A string that uniquely represents the version of the data that was retrieved. The objects of the same type and origin with the same serial number are assumed to be the same. There is no requirement for this to be identifier - the serialNumber cannot be used to retrieve the object.