Evolution of library data sets

An optical metrology system that comprises:

• a plurality of separate optical metrology tools;
• a shared library connected to said metrology tools and including a series of predicted measurement sets, each predicted measurement set corresponding to the empirical measurement sets that the metrology tools would record for a variation of a physical structure;
• an analysis program configured to search the shared library to locate predicted measurement sets that match the empirical measurement sets gathered by the metrology tools, the analysis program also configured to generate a usage pattern for the shared library, the usage pattern identifying the most common searches performed on the shared library;
• and
• a library evolution tool configured to add one or more new predicted measurement sets to the library to increase the number of predicted measurement sets within the shared library to correspond with the usage pattern so that upon a subsequent search of the library the likelihood of locating a predicted measurement set that better matches an empirically obtained measurement set is increased.