There are four broad types of healthcare IT specifications: 1) Concrete purpose-specific specifications model individual message schemas with limited reuse and no semantic interoperability. 2) Concrete generic schemas require only one schema but lead to poor semantic interoperability and different implementations of content. 3) Concrete generic schemas with formal clinical models allow clinicians to engage in modeling and improve semantic interoperability but have higher governance costs. 4) Formal clinical content models provide the same benefits as 3) and further reduce implementation costs through widespread reuse.