For DTMs inside Crawlers, this function will be called as the Crawler is being restored (in the CrawlerManager::OnOpen). However, when the crawler is being created, it will actually be called twice, once by the OnOpen, and again when Initialize is called on the Crawler. And, it will be called when Perform Operation is called on the Crawler, with a different session.
IPTDocumentTypeMap Interface | com.plumtree.server Namespace