Yes, you can do similar in a traditional RDMS, you have a table called Person and another table called Person_properties with a schema of pid, property, value,

Yes, you can do similar in a traditional RDMS, you have a table called Person and another table called Person_properties with a schema of pid, property, value, timestamp. The object model for Person would have a save() and load() method that knows which properties belong to the base table (base properties) and which properties spill over in into the triple table. The separate properties table has the convenience of stashing arbitrary persistent properties in a Person without needing to migrate the underlying schema or change the base definition.