Bridge User Manual

Appendix B Citadel and Open Database Connectivity
BridgeVIEW User Manual B-4 © National Instruments Corporation
How Do You Access Citadel Data?
The ODBC driver presents Citadel data to other applications as a Threads
table. The table contains a field or column for each data member logged to
the Citadel database.
Threads Table
The Threads table contains three fields you can use to specify query criteria
and to time-stamp retrieved data:
Interval
,
LocalTime
, and
UTCTime
.
Interval allows you to specify the query value sample rate. Interval can
range from 10ms to several years. By default, Interval is 1 (one day).
Remember, Citadel only logs a value when the value changes (it is
event-driven). But using Interval, you can query Citadel for values evenly
spaced over a period of time.
LocalTime and UTCTime indicate the time-stamps of when values are
logged. Citadel actually stores the time in UTCTime format and derives
LocalTime from the stored time. When you do not specify a time, Citadel
assumes midnight of the current day.
The following where clause from a query takes advantage of Intervaland
LocalTime to select data over a specified time at one minute intervals.
Notice that time and date formats are the same as those used in
BridgeVIEW.
SELECT * FROM Threads
WHERE LocalTime > "12/1 10:00"
AND LocalTime < "12/2 13:00"
AND Interval = "1:00"
Data Transforms
Your queries can include special commands that perform data transforms,
making it easy to manipulate and analyze historical data. The following
table lists data transform commands.