[Conference]
conference.ConferenceID="$AbstractConferenceID"
Where the conference is the name of the conference table, ConferenceID is the name of the index of that table, and $AbstractConferenceID is the foreign ID in your abstract record that corresponds to the the particular record in the conference table. Note the name of the relationship is "Conference."
In Xataface, if you have an abstract record you can quickly retrieve the related conference by simply doing this:
$conference = $record->getRelatedRecord('Conference')
This will retrieve the conference as a xataface_related_record object. It is important to realize that this is not the same thing as a xataface_record. If you want to convert this related_record object into a xataface_record object you can use the toRecord() function:
$conference = $record->getRelatedRecord('Conference')->toRecord();
This is a powerful technique that can save a lot of time.