Terms - copies vs mirrors

[Martin Hill]

Roy Williams wrote:

> 
>> So a mirror will generally always return the same results as the 
>> original. A
>> snapshot can only guarantee to return the same results up until the next
>> update of the original. An extract can never guarantee to return the same
>> results.
> 
> 
> We have astronomical datasets, called A and B.
> 
> A delivers a lossless compression of B. Are they mirrors?
> 
> When I query A and B, I get a table of results. A and B have different 
> default sorting order. Are they mirrors?

All of the above are different protocols or interfaces to the same data. 
  I would like to see separate definitions of data vs the 
interface/protocol to that data; so to me the above are all data mirrors 
(or copies if they diverge).

> 
> A delivers much lower bandwidth than B. Are they mirrors?
> 
All sites have different bandwidths that depend also on who is querying 
from where...

> A delivers data with calibration version 3.2 and B delivers calibration 
> versions 3.1 and 3.2. Are they mirrors?

no

> 
> A can deliver data from Virgo AND Orion, but B only covers Orion. Are 
> they mirrors?
> 
no


> A is available all the time, but B is located in Utah and cannot deliver 
> data on Sundays. Are they mirrors?
> 
yes. Again this is to do with protocol...

> A is the server that is mentioned in the peer-reviewed publication by 
> Professor Bigshot. The B data is a copy made by an irresponsible 
> student, and is not mentionsed in the Bigshot paper. Are they mirrors?
> 
sounds like a 'copy' to me, in that there will be no effort to keep them 
synchronised.


-- 
Martin Hill
www.mchill.net
07901 55 24 66
0131 668 8100 (ROE)