The design, rather than an account of what exists. A module provides names and
requires names, and that single relation absorbs three things this effort had
listed separately: requiring another module is requiring a concrete name,
requiring a resource is requiring an abstract one, and an interface is simply a
name with more than one provider. Nothing has to declare that it is an
interface — it either has one provider or several.
The move that does the most work: a NODE provides names too. Its profile is a
set of them — display-server, container-runtime, an architecture — so a module
requiring a display server is satisfied by the node exactly as one requiring a
database is satisfied by another module. One resolution instead of two, and a
graphical application cannot land on a node without a display server for the
same reason, through the same code, that it cannot land without its libraries.
Which makes the host's capability detection an input to resolution rather than
something a person reads. It was built to be read; it turns out to be a
provides-list.
`excludes` is the one genuinely new relation, because it is not derivable: two
modules that both provide message-bus look interchangeable when installing both
would break the machine.
Constraints are not placement. They say what must be true of a node, never which
node — which is the mistake the measurement found in the current catalogue,
where a module pins its database to a named node so a second node cannot provide
it without editing the consumer.
What it deletes, for the design: the module/resource distinction, the interface
as a kind of thing, capability checking as a separate mechanism, domain grouping
— folders assert relationships where edges record them, so a domain becomes a
query over the graph rather than a directory somebody keeps true — and possibly
tiers, if a tier is just a computed level.
What it does not delete, stated so it is not discovered later: a resolver still
has to exist, with version constraints and conflicts, and the design owes an
answer on what it delegates rather than reimplements.
jschoubben
e20a09ae80