This paper formally clarifies the relevant reasoning problems for temporal EER diagrams. We distinguish between the following reasoning services: (a) Entity, relationship and schema satisfiability; (b) Liveness and global satisfiability for both entities and relationships; (c) Subsumption for either entities or relationships; (d) Logical implication between schemas. We then show that reasoning on temporal models is an undecidable problem as soon as the schema language is able to distinguish between temporal and atemporal constructs, and it has the ability to represent dynamic constraints between entities.