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Дата изменения: Tue Jul 1 23:47:07 2008
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XMM-Newton Science Analysis System


dal (dal-1.182.1) [xmmsas_20080701_1801-8.0.0]

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Null Values

The DAL supports Null Values (both integer and real).

For objects (i.e. arrays or columns) containing integer data, it is possible to define a null value. A data value is then is considered null if it is equal to the object's null value.

Integer data containing null values may be operated on safely i.e. arithmetic operations.

In the case of real data, a value is considered null if it has an IEEE NaN representation. Real data containing null values must be treated carefully i.e. testing for nullity before carrying out any further operations.