Null-ability
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.