I was in the lobby of F&I Express last week and one of the OGs asked me, “What was that network protocol that the old IBM mainframes used?” I replied with SDLC, confidently naming the link level protocol. “No, the other one.” I moved up a level, to VTAM.
It turns out he was looking for System Network Architecture, which is not a protocol itself but the name of the stack. This was IBM’s proprietary stack, competing with Open Systems Interconnect. Where SNA had SDLC and VTAM, the OSI has Ethernet and IP. It is easy to find a chart of your favorite communication stack … except this one:
I learned about SNA on the job while studying linguistics at college, and I could not help noticing that natural language also uses a stack.
At the lowest level is phonetics. This is the equivalent of the green light on your Ethernet port. It means that you are successfully hearing the other person, although the grunts and squawks of human speech carry more data than binary bits.
The next level up is phonology, where different sounds (Greek allo-phone) are resolved into units relevant to the given language. In German, for example, /ch/ is the same in “ich” and “ach,” even though the sounds are completely different. Closer to home, English /p/ is sometimes aspirated and sometimes not, a distinction audible only to Professor Catford.
The next level up is morphology. Yes, I might as well do the whole stack, now that I’m at it. Morphology is the study of word parts that carry grammatical information, like –ing, -ed, and –es in English (and more exciting ones in other languages).
Once we arrive at the level of whole words, we can study them on their own, plus how they have changed in sound and meaning over time. The fields of comparative, historical, and social linguistics are each fascinating in their own right, but I will stick with the stack concept for now.
Grammar in Western languages is easily understood as “how to put a sentence together,” using the appropriate numbers, genders, cases, modes, and tenses. Other languages are not so straightforward, though, and the term from my day job, “message syntax” seems more correct. I have, at the moment, just finished writing a two-thousand line message syntax specification using XML.
Once we have sentences, we can have a dialogue, or “discourse level grammar.” This is the application level of the stack, and familiar to all software people. Our trade is filled with terms like dialogue, request, response, and transaction. My favorite such term, going back to my IBM days, is “pseudo-conversation.” Yes, that means just what you think it means, whether you’re talking to a bored spouse or a teleprocessor.