content, format, ctype, or xtype ?

[Alberto Micol]

> On 15 May 2009, at 15:54, Arnold Rots wrote: single Time Scale is not 
> feasible, but I think it is reasonable to restrict it to TT, UTC, and TDB 

Sorry Arnold, but given that my ignorance is almost encyclopedic 
(of everything I know almost nothing), may I ask you in simple words
to explain:

What is a plausible VO scenario jeopardised by the introduction of a single well specified time scale if that were to be used to standardise the transmission/communication of time quantities?

Suppose TT is defined to be such standard time scale:

If the original time was stored in UTC, but sent onto the wire
as TT, it could be translated back to TT without any specific extra metadata (the leap seconds are tabulated); that is not a problem (correct?).

The problem might be with the inability of translating back from TT to TDB --for those cases where 10^-2 seconds matter-- but in which scenario would that be needed? Who, in the astronomical community, is using TDB? 
And what other data/metadata would be needed to allow such TT to TDB
conversion? (though both values could be provided if really needed).

Are there other possibile scenarios?


Thanks in advance,
Alberto