Feature: CSV import/export of information object relations

Import and export of reciprocal information object relations, such as those with RAD 'Related materials" or ISAD "Allied materials", would be beneficial. The lack of import/export functionality can lead to users choosing to not use this field. This came up in the forum recently.

The issue names no files, tests, or entry points. Start by locating the existing CSV import and export paths and the information object relation model, then trace how reciprocal relations are represented; done means those relations can be imported and exported without losing their reciprocal links.

Written by the indexing model from the issue text.