I was able to create baseview from both JSON datasource (REST) and JDBC Datasources (SQL) in my Denodo 7.0 Express. You can read more about the JSON Datasources and SQL Datasources from [JDBC Sources](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/creating_data_sources_and_base_views/jdbc_sources/jdbc_sources) and [JSON Sources](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/creating_data_sources_and_base_views/json_sources/json_sources) section of the Virtual DataPort Administration Guide.
It is possible that the current installation of your Denodo 7.0 has been corrupted, Denodo re-releases the Virtual DataPort Express Edition with all the latest updates and fixes periodically. I would export the contents of my current Virtual DataPort, Download the latest Virtual DataPort Express Edition and I would import the metadata of my previous Virtual DataPort. You can refer the [Denodo Platform Migration Guide](https://community.denodo.com/docs/html/browse/7.0/platform/migration/index) for more details on migrating metadata.
If you are a valid support user, you can raise a support case and Denodo Support Team would be able to help you.
Hope this helps!