The IMatch Thesaurus is a very powerful tool for creating and managing controlled vocabularies - not only for keywords!
A controlled vocabulary (Wikipedia) is basically a list of hierarchical keywords and synonyms. Instead of manually entering keywords, you pick them from the thesaurus. This not only makes keywording (tagging) files much quicker, but it also improves the quality and consistency.
Using consistent keywords is important.
If you add different keywords for the same thing to different files, it becomes harder to find, filter and sort these files.
IMatch can fill the thesaurus from keywords already used in your files (see the IMatch help for details) and it can import thesaurus data in a variety of formats.
The simple text-based format used by Lightroom is very common, and many of the free/paid controlled vocabularies available come in this format.
To import a keyword text file designed for Lightroom, open the Thesaurus Manager in IMatch (toolbar button in either the Metadata or Keyword Panel). Click on the Import & Export toolbar button and select the Text format in the format selector box at the bottom.
Now navigate to the file you want to import and click Open...
The IMatch thesaurus automatically detects groups and synonyms contained in the file and converts them to the corresponding IMatch Thesaurus concepts. See The Thesaurus help topic for more information about groups.
After a few seconds Thesaurus Manager shows the results of the import. You can now review and edit the imported keywords as needed. Click OK to save the thesaurus to the database.
IMatch includes a default thesaurus with a set of universal hierarchical keywords. This thesaurus is automatically imported into new databases. This thesaurus is a good starting point and works well for many users.
The thesauri IMatch ships with are contained in the C:\Program Data\photools.com\IMatchN\Presets folder
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In addition to creating your very own controlled vocabulary from scratch, you can start out by using one of the many free Lightroom keyword lists available on the web. Some examples:
Lightroom Keyword List ProjectEach of these lists (or the lists they link to) have several thousand hierarchical keywords and should get you started just nicely. You can edit the keywords after importing them into IMatch to match your personal requirements and keywording habits. Maybe you export your modified thesaurus later to share it with others. Commercial Controlled Vocabularies
A good resource for both information about controlled vocabularies and high-quality commercial controlled vocabularies for many applications is the David Riecks Controlled Vocabulary web site:
Controlled Vocabulary