If you use a dedicated paragraph format for topic abstracts in your FrameMaker document, you can simply map that format to shortdesc; see §15.4.3Mapping paragraph formats to . The content of any paragraph in that format becomes the <shortdesc> element for the enclosing topic.
To add a <shortdesc> element to a topic without using a paragraph format, place a DITAShortDesc marker in the topic. The content of the DITAShortDesc marker is the text of the abstract.
Whichever way you provide the content, the resulting <shortdesc> element appears in the map, in the <topicmeta> of the <topicref> for the topic.