A relationship can't "filter" a layout but it can filter a portal. If you want to see a list of all current seminars, use a portal that uses either a relationship and/or a portal filter to only display those that are "current".
If you want to use a table view or list view layout to list them, then you'll need to build in some script triggers, but with FileMaker Advanced, it's not too difficult to do. You can use Advanced to either modify or remove the Show All Records and Show Omitted Only option so these can't be used to bring up records that aren't current.
Then write one find script that constrains the found set to current seminars and use the OnLayoutEnter and OnModeExit (Find) triggers to prevent the user from viewing anything but current seminar records on your layout.