Can anyone explain the difference between AHAH and JSON? If I'm reading it right, JSON would access data in a remote database, and it would be returned as javas

Can anyone explain the difference between AHAH and JSON? If I'm reading it right, JSON would access data in a remote database, and it would be returned as javascript and could be inserted into the page. AHAH would access remote HTML and insert it into the page? Am I wrong on that? If you used expires and caching on those static HTML pages, would that then lead to more efficient data pulling than querying a database with JSON?