Syntax versus Semantics (was: "vocabulary constraints" and otherconstra

["Costello, Roger L." <costello@mitre.org>]

Michael Sperberg-McQueen wrote: 

> if we know how to specify it formally --
> especially if we can specify it in a way 
> that doesn't require a Turing machine -- and 
> check it automatically and conveniently, we tend to
> call it (whatever it is) syntax.  If we don't know 
> how, then it's semantics.

Neat!

And Michael also wrote:

> One of the great themes of computer science 
> over the last sixty years has been the 
> long-running campaign to move more and more 
> things out of the "must be checked by 
> eyeball" / semantics area, and into the "can
> readily be checked by machine" / syntax area.


QUESTIONS

1. If something is in the realm of "semantics" does that mean it can only be processed by humans (eyeballs)? It cannot be processed by machines?


2. If something is in the realm of "syntax" does that mean it can be declaratively expressed, whereas something in the realm of "semantics" can only be procedurally expressed?


3. Suppose that something can be expressed declaratively but it takes pages and pages to express it. Is it still syntax?


I'd like to take a stab at defining syntax and semantics, incorporating 

   - the distinction of declarative versus procedural and 
   - the distinction of simple to express versus complex:


WHAT IS SYNTAX?

Something is syntax if it can be simply specified in a declarative manner and it can be checked automatically and conveniently.


WHAT IS SEMANTICS?

Something is semantics if it cannot be simply specified in a declarative manner or it requires procedural code to express it.


Do you agree with these definitions?

/Roger