You may want to swap an existing domain with a new one. For example, as system administrator you are given a new domain file to replace or update an existing domain. A server is running Microsoft English Query with multiple domains loaded and multiple user sessions attached to each domain.
You simply copy the new domain file over the old one. This will have no effect on existing user sessions using the domain; they will continue to use the old version. Each new session attaching to the domain receives the new version of the domain (with the first new session causing the new version domain to be loaded). When the last user session attached to the old version of the domain is gone, the old version of the domain is automatically unloaded.