Negative Match Conditions

Match conditions are statements that indicate which fields you want to match in order for two records to be considered a match. However, in some situations you may want to define a condition that says that two fields must not match in order for two records to be considered a match. This technique, known as negation, reverses the logic of a condition within a match rule.

For example, say you have customer support records for a call center and you want to identify customers who have contacted the call center but done so for multiple accounts. In other words, you want to identify individuals who are associated with multiple accounts. In order to identify customers who have multiple accounts, you would want to match records where the name matches but the account number does not match. In this case you would use negation on a match condition for the account number.

To use negation, check the box Match when not true when defining your match rule. This option is available to both parents (groups of conditions) and children (individual conditions) in the match rule. The effect of this option is slightly different when used on a parent as opposed to a child. When used on a parent, the Match when not true option effectively reverses the matching method option as follows:

The All true matching method effectively becomes "any false". The match rule can only match records if at least one of the children under the parent evaluates to false, thus making the parent evaluate to false. Since the Match when not true option is enabled, this evaluation to false will result in a match.
The Any true matching method effectively becomes "none true". The match rule can only match records where none of the children evaluate to true because if any of the children evaluate to true, the parent will be true, but with the Match when not true option enabled, this evaluation to true will not result in a match. Only if none of the children are true, resulting in the parent evaluating to "not true", can the rule find a match.
The Based on threshold matching method effectively changes from matching records that are equal to or greater than a specified threshold, to matching records that are less than the threshold. This is because records with a threshold value less than the one specified will evaluate to false, and since Match when not true is enabled, this will result in a match.

The Match when not true option is easier to understand when applied to child elements in a match rule. It simply indicates that two records are considered a match if the algorithm does not indicate a match.