A.2 Determining the first or last historical data point

In some cases, Servers are required to return the newest or oldest available data point for a historical Node; Clause A.2 recommends the way that a Client should request this information so that Servers can optimize this call, if desired. Although there are multiple calls that could return the first/oldest data value, the recommended practice will be to use the StartOfArchive Property.

If this Property isn’t available then use the following query using ReadRawModifiedDetails parameters to get the first/oldest value:

• returnBounds=false

• numValuesPerNode=1

• startTime=DateTime.MinValue+1 second

• endTime= DateTime.MinValue

• If the last or most recent value in history is required use the following query:

• returnBounds=false

• numValuesPerNode=1

• startTime=DateTime.MinValue

• endTime= DateTime.MaxValue

• The DateTime.MinValue indicates that no specific time is specified. This is a special value that a Server must be aware of (see Table 27).

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