# Event representation

Events are represented "on the wire" in a JavaScript Object Notation (JSON) format. At the top-level, an event is a JSON array with elements corresponding to the following.

1. Subject ID

2. Start date

3. End date

4. Domain name

5. Flags

6. Event

The information provided by many of the top-level elements is fairly self-explanatory so we won’t mention them here. One less obvious element is the "flags" entry which is used to provide 0 or more context-specific labels for an event such as e.g. "statin_rx" or "hip_fracture_dx". Also of particular importance is the context, which as mentioned above provides information about what the event represents. Again, one can guess what information is provided by many of the elements of the context object, but we note here that the facts object is of central importance to the EDM, and the structure of which will be the main topic in this site.