Signs are related to models of reality along two dimensions: the surface dimension (phonology or orthography), and the semantic dimension.
Surface space-time structure (phonological and graphemic), and semantic domain structure, are defined as projections of ID structure. The structure of both of these domains is determined by the structure of the physical machines used to create and analyse (produce and perceive) these domains. The core structure is linear, i.e. non-hierarchical, and procedures in these domains can be modelled by finite state machines. Any more complex non-hierarchical features of these domains are epiphenomena generated by interactions between finite state machines.
The LP domain (enhanced by prosodic relations to the QLP domain) is linear, and models human faculties as a physical machine. Any apparent hierarchical properties are projected from the ID level, and not properties of the LP or QLP domain. Properties of the QLP domain which appear to be hierarchical (e.g. stress patterns, or parentheses) are epiphenomenal, and generated ad hoc by additional cognitive mechanisms. They have drastically limited depth (two or three, bottoming to a linear, iterative structure - ``restart'')
The semantic domain models human faculties as a physical machine enhanced by additional social, cultural and physical storage mechanisms.