Properties (fields) can be added to a structure if/when needed.
When retrieving, adding or updating data use the property (field) alias.
Examples;
mydigitalstructure.cloud.save({object: '_structure_1', fields: {_field1: '..', _field2: '..'}});
mydigitalstructure.cloud.search({object: '_structure_1', fields: ['_field1', '_field2']}});
mydigitalstructure.cloud.save({object: 'contact_person', fields: {firstname: '..', _field1: '..'}});
mydigitalstructure.cloud.search({object: 'contact_person', fields: ['firstname', '_field1']}});