Data lookup definitions fields Data lookup definitions fields. Table 1. Data lookup definitions fields Field Description Name Enter a unique name to identify the definition record. Source Table Select the table containing the fields you want to automatically update with lookup values. Data Lookup Definitions are not inherited by extension tables. For example, a Data Lookup Definition on the Task table cannot match values on the Incident incident table. Matcher Table Select the table containing the lookup values. This table should always start with a u_ prefix. Active Select this check box to run this data lookup rule. Clear the check box to ignore this data lookup rule. Run on form change Select this check box to automatically look up values whenever a user or onChange client script changes a field value on a source table form. Note: This does not include changes automatically made by other data lookup rules, such as the Priority Lookup Rules. Run on insert Select this check box to automatically look up values whenever a user creates a new record. Run on update Select this check box to automatically look up values whenever a user saves or updates a record.