Good question, the problem is that it depends on the definion of the terms, I think they differ slightly based on the sources.
I would agree with previous answer – domain models are for describing the problem domain, at least the part you need to develop a solution. You describe all the various entities, their relations and their behaviour. I think that this is also the view from the Domain Driven design perspective.
Data models on the other hand are used for describing the data in your system and relations or associations between them. This is useful for describing what needs to be stored in the system and might also give hints how. I think data models would apply for your “no operations” rule, because they are not important in this respect.
