Abstract: A data structure indexes identifiers corresponding to parameter patterns. The presence of an identifier in the data structure indicates that the corresponding parameter pattern may be present in a set of parameter patterns, while absence of the indicator can be used to indicate that the corresponding parameter pattern is not present. The data structure includes a first field which includes small parameter pattern records. Each parameter pattern record corresponds to an identifier corresponding to a parameter pattern. If the record corresponding to the identifier is set or present, the identifier is included in the first field. One or more additional fields are hierarchically below the first field. Each of the additional fields includes identifiers for a subset of information in the first field. The absence of an identifier corresponding to a parameter pattern at any level in all of the hierarchical threads indicates that the parameter pattern is not present.