Thanks for the background and for taking the time to answer my question. This was very helpful.
I have not had a chance to participate in this very active thread,
but I'd like to elaborate on a point that Ed made:
Well, you get a ‘semantic network’, if that is what you mean
by “Semantic Web”.
Yes. Description logics began with Aristotle. The idea of organizing
them in a tree was first recorded in the 3rd century AD by Porphyry.
But similar diagrams were probably drawn much earlier.
For an overview of semantic networks from the early days to the present
For more detail, the following article relates Peirce's existential
graphs and my conceptual graphs to a wide range of notations --
Peirce discovered RDF (with blank nodes for existential quantifiers)
around 1882, and he added negation in 1897 to support full FOL. In
1898, he added metalanguage to allow assertions about any graph or
subgraph. By 1906, he added modal logic and higher-order logic.
Figure 28 of eg2cg.pdf shows how the usual music notation can be mapped
to a CG (and from a CG to Common Logic or many other notations).
I agree with the comments by Pat Hayes, who pointed out that the
"opinions" being discussed in this thread have been kicked around in
AI for the past half century -- and by logicians for over a century.
And yes, URIs are useful. But you can treat URIs as names in
any version of logic.
To respond to a question by Frank:
Can I ask you (or anyone who might know the answer) to clarify why
they're called "Assertions"?
This gets into the distinction between natural types and role types.
You can say that the meaning of a sentence (or a formula in logic)
is a proposition. That is the most neutral term for what it is.
But that proposition (or the sentence that states the proposition)
can play many different roles: If you state it, it's a statement.
If you assert it, it's an assertion. If you assume it, it's an
assumption. If you use it to define something, it's a definition.
My recommendation is to use the word 'sentence' or 'formula' for
the marks that are written on paper or your computer screen.
Then you can say that the notation-independent meaning of that
sentence is a proposition. All the other terms are roles that
the sentence or the proposition happens to play.
For more about the distinction between sentences and propositions,