Significance of required data

If you define an occurrence of a component as required, you are saying that, for the data containing the component to be valid, this component must exist. If it does not exist, the data is invalid.

For example, if you define Record as having the component Field (3:3), you are saying that there must be three Fields in the Record. If there are not three Fields, then either it is a Record in error or it is not a Record.

There are other factors, besides the existence of all required components that make data valid. The existence of required components is necessary, but not sufficient, for data to be valid.