Lookup tables
Lookup tables contain a set of definitions. Rules can reference lookup tables as part of actions or conditions.
- An action or condition can compare a particular value to a value in the lookup table. For example, a condition can stipulate that a rule handles a record only when a value in a particular position in the record is in the lookup table.
- An action can convert a particular value to a value in the lookup table. For example, an action might use a lookup table that contains geographic information to convert numeric place codes to place names.
Some rule sets use one or more lookup tables. For example, a lookup table that contains the gender that is associated with particular names is included in the name rule sets.
Lookup tables are added and modified by adding or editing .TBL files or enhancing a rule set under Manage.
Lookup table definitions
A lookup table definition includes the value that is looked up, a returned value, and a similarity threshold.
- Value
- The string of one or more characters that you want to add a lookup table definition for.
- Returned value
- A string of one or more characters that can be used by an action or condition in a rule instead of the value. If you do not specify a returned value, it is the same as the value.
- Similarity threshold (previously called threshold weight)
The degree of variation that can exist in the spelling or representation of the value. If you want the definition to affect values that are different from the value in the definition, you can set the similarity threshold lower than the default of 900.
The similarity threshold must be an integer in the range 700 - 900. The integers represent the following degrees of variation:- 900
- Strings must match exactly.
- 800
- Strings are almost certainly the same.
- 750
- Strings are probably the same.
- 700
- Strings are probably different.
When the rule set that contains a lookup table definition is applied to data, values in the data are compared and a score is assigned. This score indicates the degree of similarity between two values. The string comparison method that is used can take into account phonetic errors, random insertion, deletion and replacement of characters, and transposing of characters.
The score is weighted by the length of the value because small errors in long values are less serious than errors in short values. Because errors in short values cannot generally be tolerated, do not specify a similarity threshold for short values.