A field is required only where its value is guaranteed
A field is required where every data record that can hold it has its value: the value is set before the data record is written, the system makes or observes it whenever it writes the data record, or the system refuses to write the data record without it, as what identifies the data record. Every other field is optional: one whose value only some data records, or some moments of a data record, have, or one an answer the system reads may not carry.
A value that may not come cannot be demanded: demanded, it is invented to fill the field, or a data record that should have been written is refused for want of it.
The links it makes
The decisions taken on it
- Problem
Nothing said when a field of a data record is required, so values that may not come were declared required, and a value carrying nothing was given a form holding nothing.
- Ruling
The owner: formal fields, set beforehand or made by the system, are required; additional fields are required where their case guarantees them, as an identifier an external system gives a data record that cannot exist without it, and optional otherwise, as an external system's answer.