When I start talking about InterSystems IRIS with more technically-minded people I always talk about how at the root of things it is a multimodel DBMS.
In my opinion that is the main advantage (on the DBMS side).
You want some sort of summary for your data? Use SQL!
Do you want to work extensively with one record? Use objects!
Want to access or set one value and you know the key?
Think again. Use globals!
And the data is stored only once. You just choose the way you want to access it.
On the first overview it's a nice story - short and concise and it gets the message across, but when people really start working with InterSystems IRIS the questions start.
How are classes and tables and globals related? What are they to each other? How's data really stored?
In this article I would try to answer these questions and explain what's really going on.