Anyway, Udi, after reading your blog, I have to agree. SOA = HST + RSA.
But let me coin my own silly catch phrase: SOA is like scissors and glue, the scissors and the glue that allow you to both HST and RSA. Let’s just suppose, for god sake, that the interviewer misunderstood Pat Helland when he said “sheet”.
Neither RSA nor HST is a new thing. RSA has been a primary engineering task from day one, and HST from day two. They are actually two sides of a same coin.
I believe that what is really new is the set of enabling technologies under the SOA umbrella and the set of activities they enable. Those tools make both RSA and HST easier in software development. With SOA, some choices that used to be expensive are a lot cheaper.
For instance, re-implementing a perfectly functioning part of a system just for the sake of framework standardization makes less sense than before because of SOA glue that enables HST. But building a service facade for an existing subsystem is no trivial work either. You still have to balance.
On the other side, building new systems from autonomous services makes more sense than ever. Not only SOA scissors enable us to do it in elegant ways. Ripping it apart properly from day one will make hooking it together a lot cheaper on day two.
Now, as a side note, I have been involved in projects that could have made good use of HST, but they didn’t. I feel guilty today.