In the PPDM data model, only the columns defined as primary key are set to Not Null. All other columns are set to null.  This is the default.  If you have a business rule or implementation design decision that states something like "all areas must have a coordinate system", then you could change the Coord_System_Id column in the AREA table to Not Null.  This will impact all future usage of the table because every row that is stored in that table must have a value in that column. That is a big impact on the usage of the table both in cleanup of existing data as well as potentially altering applications to properly capture this information when a row is created.  It might be better to create a batch job that finds any rows in the AREA table where the Coord_System_Id column is null and email the owner (source) of the row with a request to update this column.
If an implementing company decides to set the PPDM_GUID value to ‘Not Null’, there is a script available; as part of the 3.8 release, that will change the data model.  There is also a script that will put a unique index on each table as well.