Explainer
When the Source of Truth Is a Model
The Shift
From Drawings to Definitions
The technical data package — the contractual definition of a product, governed by MIL-STD-31000 (currently revision B) — comes in two types: the traditional 2D drawing package, and a 3D type where the definition lives in digitally connected model files. The 3D approach, Model-Based Definition, makes the annotated model itself authoritative; drawings, where they exist at all, are derived views. DoD's digital-engineering policy direction reinforces the same principle: models as the source of truth, kept accessible and usable for decades. The much-invoked digital thread is this idea extended through the lifecycle — design data flowing to manufacturing, sustainment, and yes, documentation, without being re-keyed at each border.
Technical publications have always lived at the end of that chain: someone read the drawings and wrote the manual. The question the model-based shift poses is whether that hand-off stays human transcription — or becomes a data flow.
The Last Mile
Publications Are the Thread's Delivery Layer
The breathless version of digital-thread rhetoric implies the model replaces the manual. It won't — a maintainer needs a validated procedure with warnings in the right order, filtered to their configuration, on a device that survives a flight line. What changes is the manual's supply chain: illustrations generated from model geometry rather than redrawn, parts data flowing from the model's structure into IPD modules, procedures tracing to the design elements they touch. The S-Series family already runs this philosophy — analysis data upstream, publications downstream, one configuration view — and model-based TDPs extend it to the design definition itself.
The readiness test for a tech pubs organization is unglamorous: connection requires structure on both ends. Publication source that is structured and addressable, identifiers aligned so content can reference design data — identifiers are architecture, again — and illustration pipelines treated as the first practical bridge, because model-derived graphics are the mature piece today. Organizations still authoring from PDFs of drawings aren't one step from the thread; they're two, and the first step is the same structured foundation every other future in this series requires. The thread rewards the prepared.
FAQ
Questions We Hear
What is a model-based technical data package?
MIL-STD-31000 — the standard defining technical data package requirements, currently at revision B (2018) — recognizes two TDP types: the traditional 2D drawing-based package, and a 3D type where the product definition lives in digitally connected model files. In the 3D approach, called Model-Based Definition, the annotated model is the authoritative product definition rather than drawings derived from it. DoD's broader digital-engineering policy direction pushes the same way: the model as the source of truth, kept accessible and usable for decades.
What does that mean for technical manuals?
It relocates their upstream source. Manuals have always been derived from product definition — someone read drawings and wrote procedures. When the definition is a model, derivation can become partly a data flow: illustrations generated from model geometry, parts information drawn from the model's structure, references that trace back to model elements. The manual stops being a hand-made interpretation of the design and starts being a downstream product of it — which is exactly how the S-Series family already treats the relationship between analysis data and publications.
Does the model replace the publication?
No — and this is the trap in the more breathless digital-thread rhetoric. A maintainer on a flight line needs a validated procedure with warnings in the right places, filtered to their configuration, on a rugged device — not a CAD session. The publication remains the product the human consumes; what changes is its supply chain. The realistic architecture keeps structured publications (S1000D data modules and their kin) as the delivery layer, increasingly fed and updated from model data rather than transcribed by hand.
What should tech pubs organizations do about this now?
Position for connection rather than transcription. Concretely: keep publication source structured and addressable (a prerequisite for any automated feed), align identifiers so publication content can reference design data (the same 'identifiers are architecture' lesson as the DMC), and treat illustration pipelines as the first practical bridge — model-derived graphics are the most mature piece of the story. Organizations still authoring from PDFs of drawings have a two-step journey; the first step is the same structured-content foundation everything else in this series requires.
Get In Touch
Ready for the Thread?
If your publications are hand-transcribed from drawings, the model-based era arrives as a gap. We build the structured publication layer the digital thread can actually feed.