Operational viewpoint - isn't that "Infrastructure"?

No!!!!

Yes, OK, I agree that, just like "operational" has a formal meaning (a viewpoint looking at the placement and distribution of the IT System), so can "infrastructure", but I think it's a different, equally powerful idea.

Infrastructure - the stuff you can't (or maybe choose not to) see. 

• From my favourite search engine: "the basic physical and organizational structures and facilities (e.g. buildings, roads, power supplies) needed for the operation of a society or enterprise."

Electricity cables underground,  sewerage pipework. And even if you can see it - roads, telephone exchanges and so on, it's all the physical things we need behind the scenes to live our daily lives more comfortably.

So it is with IT systems - the infrastructural viewpoint focuses on the underlying software and hardware needed... maybe I should say we system designers decide is needed to keep the (business) applications and data going, working in conjunction with users and support professionals, day in, day out.

And, critically ( but oft forgotten) there is therefore every bit as much a need to think about infrastructure from the functional viewpoint as there is when looking from the operational viewpoint.

In other words, software engineers concern themselves just as much as systems engineers about "transaction management" and "Backup-and-recovery", whether in the form of middleware or hardware.  Unsurprisingly, they have a different emphasis, for example developers are more likely to focus on how their application exploits the SQL functionality of an RDBMS, rather than the RDBMS's distributed data management capabilities - in which the systems engineer is far more interested.

Put otherwise, it is insightful - I'd say vital - to recognize how infrastructural concerns are orthogonal to those of the functional and operational viewpoints; that when thought of as a wholly separate notion they provide a powerful means of "joining" the functional and operational worlds.