Originally Posted by nekokami
I think tags are usually just concatenated in a single database field, freely, and selected on the fly. But I could be mistaken-- perhaps the software parses them and stores them in a separate table, as you suggest.
Yes and no. They are usually presented to the user in 1 field. However, to be able to do quick sorting on them they would be broken up into the database with a tags table and a tagsbooks table. The tag table will will include each tag once, then the tagsbooks will link the tag table to the books table.
If you just put them all in one field you have to scan through each record to pull out tags, etc. While indexed records can be retrieved so much faster.