There is a lot of value if the DB API is abstract enough, like:

    (id) addBookmark(title,url,taglist)
    (bookmark) getBookmark(id)
    (array) searchBookmarksByTag(taglist)

And so forth. You can switch from SQL to a NOSQL solution and so forth without to touch the app but just a single file with all the DB API.

If it's at very low level like Db.get(), DB.set(), ... is still useful if the application just using a strict common subset of features (get/set/exists/expire/incr).