I have written before about the recent return to the bi-temporal databases, in conjunction with DB2. In the 1990-ies was the first attempt to create bi-temporal extensions to SQL, at that time there was a language war, some of it is reflected in the book that I have co-edited, published in 1998. Now after some attempts, SQL:2011 does include support in bi-temporal databases. The terminology was changed from the original terms. What was called in the original version - "valid time" is called in the SQL version "application time', an what was called in the original version - "transaction time" is called in the SQL version "system time".
More details about the SQL extension can be found in the overview presentation that Craig Baumunk uploaded to slideshare. As I have written before, temporal database is vital for maintaining historical events, and thus the importance of this standard, and the supporting databases to event processing application is noticable
