Final answer:
The main characteristic of the HIE monolithic architecture is the use of a centralized database that stores all health information, accessible by providers and authorized entities.
Step-by-step explanation:
In the Health Information Exchange (HIE) monolithic architecture, the main characteristic is a centralized database. This type of architecture involves having a single, central database that stores all patient records and health information. Providers and authorized entities access this central repository to upload and retrieve health data. With a monolithic HIE, interoperability challenges could arise, as every participant needs to connect to this central system. Moreover, managing and securing the centralized database is critical, as it becomes a potential single point of failure and a target for security threats.