Create new project proj-a. Add the single .sql file with CREATE TABLE statement that creates table TA. Check $PROJECT DDL$ data source: it shows new table. Create new project proj-b. Say to open it in a new frame. Add the single .sql file with CREATE TABLE statement that creates table TB. Check $PROJECT DDL$ data source: it starts to act inconsistently. For me on this step it usually shows only TB table. Then close project proj-b. Now only proj-a is opened, but $PROJECT DDL$ still shows TB. Navigation from TB opens corresponding .sql file in proj-a. Etc, etc.