- World 1 of physical object and events, accessible by all human beings given the right perceptions or equipment
- World 2 of mental objects and events, the inner world of human being accesible by only this human, and
- World 3 of objective knowledge that comprized the products of human thought - ideas, theories, stories, myths etc.
I think that the difference between Systems Integrator/Engineer and Specialty Engineers is fundamental and stems from the difference in their World 3 products (as encoded in information artefacts):
- Specialty Engineers (SpecIs) encode their mental models in executable information artefacts that allow production of physical objects by machines or skilled humans that don't have to share the engineers mental models. Examples - computer code is used by compiler/builder to encode physical computer file that may be run by a computer, mechanical drawing allows production of parts by workers/robots, electrical diagram allows to produce a circuit.
- Systems Engineers'/Integrators' mental models are encoded in information artefacts (or even communicated without physical encoding building the common understanding -the pure World 3 object) that are meant to create compatible mental models in the minds of other engineers. In that SE/SI are just like to architects, managers and leaders.
The line of distinction between SE/SIs and SpecIs may move with the evolution of technology - once non-exectutable information artefacts may become executable - one example is executable specifications/models that once needed skilled programmer (SpecI) to convert them to the executable code and now this job can in some cases be done by a machine.
It's common that engineers perform both roles of SE/SIs and SpecIs so they have to be educated in these fairly distinct skill sets.
Summarizing: SpecIs produce executable information artefacts meant to be used in production, SEs/SIs produce World 3 objects meant to communicate mental models between engineers and other professionals, without directly leading to the production.