Denodo Data Catalog tool is designed to help non technical users explore the database elements based on their search criteria. Since association only allow left outer join between two views, in order to apply other joins over the views, I would prefer using Virtual DataPort Administration tool with the help of developers.
Adding to that, instead of creating an association manually in Virtual DataPort Administration tool, I would import the foreign key relationships in the underlying data source as associations by using the Discover association feature. This will help me to retain associations in Virtual DataPort without any issues as long as the foreign key maintains referential integrity in the underlying data source. You could refer to [Creating Associations for JDBC Base Views Automatically](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/restful_architecture/associations/creating_an_association#creating-associations-for-jdbc-base-views-automatically) section of Virtual DataPort Administration Guide for more information.
Hope this helps.