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Handling NULL values

The interface treats NULL's by introducing a single valued function 'NULL'/1 whose single value is a unique $($Skolem$)$ constant. For example a NULL value may be represented by

Under this representation, two distinct NULL values will not unify. On the other hand, the search condition IS NULL Field can be represented in XSB as Field = 'NULL'(_)

Using this representation of NULL's the following protocol for queries and updates is established.


Baoqiu Cui