FileMaker Extra: Indexing in FileMaker
One of the more significant changes beginning in FileMaker 7 revolves around indexing. In prior versions, indexing was restricted to 60 characters total, broken into blocks of up to 20-character words. Relationships had to be built around match fields or keys that were relatively short and generally nondescriptive. This fact is one reason we generally advocate using simple serial numbers for indexing purposes. It's rare that you'd need more than 20 digits to serialize the records in a data table.
FileMaker 10 can index words up to approximately 100 characters. It can index text fields to a total of 800 characters, and numbers up to 400 digits. The limits to indexing have been effectively removed.
What this means to developers is that you can now use far more complex concatenated key combinations (ironically, there will be less of that in FileMaker 10, given that data can be related across multiple tables), use longer alphanumeric keys, or, as suggested earlier, introduce descriptive elements to keys.