Field's dependency in Sourcing 10

Dear Colleagues,
I have two questions about field's dependency in SAP Sourcing 10.

1. Is it possible to make a field which is depended on document's phase? For example, in phase "A" field will be non-editable and hidden. After changing phase to "B", this field will become editable.

2. Is it possible to make a field which is depended on the other field? For example, we have two extension definitions, both value list type. In the first of them we would like to have only two possible options to choose from. The values in the second extension field should be depended on the choice we made in that first field.

Thanks in advance,
Przemyslaw