I suggest to start by limiting to discussion to any attribute stored with the 'data' (i.e. not every attribute traveling with the data to/from and between servers) ..
E.g. Consider X-Delete-At  while not considering X-Delete-After (as it is never stored with the data)

Another somewhat non-orthodox classification is between USER and SWIFT as the entity creating  the metadata: 
- If the system is ok with the user generating the information (and even if it is in practice being also generated in some cases by a middleware) the attribute would be considered as a USER MD (E.g. we have a middleware that will set X-Container-Sync-To but we will still consider it to be a USER MD. 
- If the system is enforcing the information (and even if it tested against some user provided information) we will consider it as a SWIFT MD. E.g. ETag is enforced by Swift, yet the user may send his own version which will be tested against the system version. 

Objects Metadata: 


I suggest to start by limiting to discussion to any attribute stored with the 'data' (i.e. not every attribute traveling with the data to/from and between servers) .
E.g. Consider X-Delete-At while not considering X-Delete-After (as it is never stored with the data). I guess a very similar analysis can be made on the incoming/outgoing headers – which may make sense also, but we need to start somewhere…

Another somewhat non-orthodox classification is between USER and SWIFT as the entity creating the metadata: 
- If the system is ok with the user generating the information (and even if it is in practice being also generated in some cases by a middleware) the attribute would be considered as a USER MD (E.g. We have a middleware that will set X-Container-Sync-To but we will still consider it to be a USER MD. 
- If the system is enforcing the information (and even if it tested against some user provided information) we will consider it as a SWIFT MD. E.g. ETag is enforced by Swift, yet the user may send his own version which will be tested against the system version. 

I created a google docs page to summarize the different Metadata attributes I have found so far.
See: https://docs.google.com/spreadsheet/ccc?key=0Anreg7c52mt0dGJUb2xyWHltMWdxalE3cEF6azFrRGc#gid=0
whoch should be open for everyone to read (anyone interested in editing at the source, please send me your gmail).


Coming from this, here is a first version of suggested classification in Swift:

                                                             Generated by the User                     Generated by Swift
                                                        Can be read	              Hidden           Can be read	           Hidden
Modulates Swift	                Control MD	           <<Never>>	Swift MD	      Internal MD
Does not modulate Swift	User MD	           <<Never>>	Swift MD	      <<Never>>

Or in other words: 
- Control MD is any MD that controls/modulates swift (and can be read and written by the user)
- User MD is any MD that the user stores in Swift and Swift and does not controls/modulates swift 
- Swift MD is MD generated by Swift that the user can read and may also control/modulate swift 
- Internal MD is MD generated by Swift, hidden from the user (i.e. used internally)