How can I prevent duplicate structures from being registered?
The best way to do this is to create a second database that you use to add new records to, then import this second database into your existing database and use the Merge feature. So, say you have an existing database, and you decide you want to add a record, but you're not sure if the record already exists. Create a new database, and add the new structure to it. Now choose Export as SD File from the File menu. Now open your existing database and choose Import SD File, and choose the Merge option when prompted. If the structure is found in the existing database, a new record will not be created. Instead you will be prompted to decide what you want to do with the non-structural data.