you should not specify abap perspective 
. Using DDL Source, you can not create tables(and hence new independent entities).As of now DDL source is a data extraction technique , and hence it is a view. If you want to create a new entity, you have to create a table from abap workbench and use them in the DDL source .
CDS views will create database views in the abap schema referring to the artefacts which we refer in the DDL source. We are(no external techniques) are allowed to create tables in abap dictionary .
Sreehari