Wasabi is an effort to create a unified searching and metadata storage specification for the free desktop. This document contains draft specs meant for further discussion.
Apple's metadata filesystem - stores file metadata in seperate database, import for common and customized file metadata, sophisticated api and command line query
S. Pandya, P. Virparia, and R. Chavda. International Journal on Soft Computing, Artificial Intelligence and Applications (IJSCAI), 5 (1):
09 - 15(February 2016)