Support for required and optional datasets in flow/model definition

[greg-wiltshire]

Feature Request

Description of Problem:

In some calculations some datasets for a model or a flow may not be required by the code. An example would be to rely on default parameters/calculated values by default but to have the option of providing a dataset to trigger alternative logic flows.

A second example would be when running a calculation that adds a snapshot or delta to a existing dataset. When this first runs the dataset to add to will not exist but will need to be specified from then on as one of the inputs. To enable this scenario the dataset needs to be set as optional.

Potential Solutions:

Add to the flow and model definitions the ability to flag each input as optional/required.