A Catalog describes functions, ins & outs of the workflow. So, in order to have a workflow, we need catalog.
A catalog is a vector of maps which must be compsed with onyx keywords :onyx/name, :onyx/plugin, etc.
A workflow could be think as a place where the structure of a computation is isolated.
Workflows can split and then merge again.
Catalogs of type :input & :output talk to plugins, those of type :function, need to pass the name of a function into :fn.