open-standards/aac

AAC

A carrier for voice. A communication board is a signed, portable file — every symbol, every language, every access method — that speaks on any device, offline, owned by no one.

AAC is the communication cargo class of the Transaction Science substrate. Where Smart Byte carries value, EOC carries compute, Map carries place, and Joule Code carries coding work, AAC carries utterance — what a non-speaking person means to say — as a content-addressed, portable board with its access model and its energy cost intrinsic.

Augmentative and alternative communication is the assistive technology that gives a voice to people who cannot rely on speech: children and adults with autism, cerebral palsy, ALS, stroke, apraxia, Rett syndrome, and many other conditions. A board is a grid (or a visual scene, or a keyboard) of cells; selecting cells composes an utterance; the device speaks it. The selecting can be done by touch, by a single switch scanned across the grid, by where the eyes rest, by a head pointer, by a joystick — whatever motor channel a person has.

A board in this standard is not an app's private save file and not a vendor API response. It carries exactly what a voice needs to survive moving between devices: identity (a content address over its canonical serialization), a layout (cells placed once and locked, so muscle memory is never invalidated), symbols (referenced by source and stable id, not baked-in pixels), an access model (the method, timing, and calibration the user relies on), language (a graph edge, so a bilingual user code-switches by traversal), and a two-part joule cost on every operation — for transparency, never billing. Communication resolves through an explicit energy-tiered cascade: the overwhelming majority of utterances are cache hits and on-device lookups that never touch a network, and richer help (context-aware prediction, sentence construction, voice cloning) is reached only when something cheaper cannot close the request.

The substrate is intentionally ownerless: no protocol-level token, permissive licensing on the spec text and reference code, and conformance vectors so any implementer can verify canonicity without a trust relationship with the authors. A conforming client opens a board, renders it, drives it with the user's access method, predicts on-device, and speaks — against local storage, with no contact with any company's servers as a condition of operation. Transaction Science is one steward: it publishes the spec, ships the reference implementation, and operates optional commercial services (hosted symbol libraries, voice banking, team coordination) around the substrate — not its proprietor.

The doctrine

A voice is a file, not a subscription. The durable layer of a communication system is not the app and not a recurring charge — a person's ability to speak must not lapse when a payment does. It is the portable, self-describing board that renders and speaks forever from dumb storage, on any device the user already owns.

Seven principles, normative in SPEC.md:

1. Free forever. No billing, no tiers, no balance, no in-app purchase. Every cascade level is free at the protocol layer. A conforming implementation never gates communication behind payment.
2. Offline first. Levels L0–L2 — cache, symbol lookup, local prediction — run entirely on-device and carry 95%+ of communication. A network drop never silences a user.
3. Motor stability. Cells are placed once and locked. Symbols do not move; layouts do not reflow. The user's motor plan is sacred — a board that rearranges itself has destroyed the thing that made it usable.
4. Every access method. Touch, switch scanning (1- and 2-switch, row-column, group, linear), dwell/eye-gaze, head tracking, joystick, partial voice. No method is an afterthought; each is a first-class input in the same model.
5. Every language. Multilingual is a graph edge, not a separate app. Code-switching is traversal. RTL, CJK, Indic, and Arabic scripts are first-class.
6. Open interchange. A board exports to and ingests from the open interchange format. A user brings their existing boards in and takes everything with them when they leave. No lock-in — ever.
7. The receipt. Every operation reports a two-part energy cost in microjoules with an honest provenance tag. The cost is shown for transparency and is never converted into a charge.

The cascade

AAC's organizing primitive is the energy-tiered cascade — ten levels, each an order of magnitude costlier than the last, each reached only when nothing cheaper closes the request:

Level	Name	Typical op	Energy	Offline
L0	Cache hit	recently-used phrase, pinned message, motor-planned sequence	~1 µJ	✅
L1	Symbol lookup	core vocabulary retrieval, symbol-set search	~10 µJ	✅
L2	Local prediction	on-device word/phrase n-gram completion	~100 µJ	✅
L3	Context prediction	time / place / partner / activity-aware prediction	~1 mJ	—
L4	Semantic expansion	novel sentence construction from partial input	~10 mJ	—
L5	Conversation AI	conversation repair, social scripts, pragmatics	~100 mJ	—
L6	Generative communication	letters, posts, longer narratives	~1 J	—
L7	Voice clone	personal-voice synthesis from recordings	~5 J	—
L8	Multimodal generation	custom symbol / visual-scene synthesis	~10 J	—
L9	Adaptive model	retrain the user's prediction model	~15 J	—

The boundary at L2/L3 is normative: exactly L0–L2 are offline-capable, and a conforming client serves them with no network. Everything above is enrichment, never a dependency.

Open interchange

A user's years of customization — added words, custom symbols, personal phrases, the exact layout their muscle memory has learned — are the most valuable and least portable thing in assistive technology. AAC makes interchange a property of the standard: a board serializes to a canonical, self-describing form, and the reference engine ingests the open board interchange format and other community exports so a user never starts over when moving in, and never loses anything when moving on. Ingestion is one-directional and additive — the standard reads existing work into the substrate; it does not compete with the tools that produced it.

Contents

• SPEC.md — the normative specification (RFC 2119): the board / cell / symbol data model, the access-method abstraction, canonical serialization, the cascade and its offline invariant, the interchange format, and the receipt.
• spec/ — sub-specifications: the board data model, the motor-stability invariant, the access model, the communication cascade, interchange, and the receipt.
• vocab/ — the controlled vocabulary (LEXICON.md) and stable IRIs: the OWL ontology (v1.ttl), the JSON-LD 1.1 context (v1.jsonld), and SHACL shapes (v1.shapes.ttl). Namespace https://aac.transaction.science/vocab/v1#.
• conformance/ — published vectors. An implementation is conformant if it reproduces them.
• aac-rs/ — the Rust reference: aac-core (the engine — boards, symbols, vocabulary, motor planning, scanning, dwell, prediction, i18n, interchange), aac-web (a reference communication app built on Leptos), and aac-conformance (the harness).

Reference implementation and demonstrator

The Rust reference lives in aac-rs/. aac-core is the engine a third party implements against — platform-agnostic, dependency-light, no UI. The demonstrator is aac.transaction.science: a free communication app (Rust → WASM, offline-first PWA) that consumes aac-core and renders grid boards, switch scanning, dwell selection, gamepad and eye-tracking input, on-device prediction, and system / banked-voice speech. The demonstrator is a demonstration of the standard — free forever, every access method — not a product to be sold.

Status

v0.1.0 draft. Reference engine ported and building: aac-core (22 modules — boards, symbols, vocabulary, motor planning, switch scanning, dwell, prediction, context, history, multilingual, accessibility, partner tools, analytics, the cascade router, the store, interchange import/export), aac-web (the Leptos reference app), and the aac-conformance harness (cascade routing, energy monotonicity, the offline invariant, and wire round-trips). cargo test and cargo clippy --all-targets are green on the engine and the harness. The reference app builds end-to-end through cargo leptos build --release — both the WASM client (aac-web.wasm, ~3 MB) and the SSR server binary — and boots: it serves the app shell and the offline-first PWA assets. Specification core published in SPEC.md and spec/, with the controlled vocabulary and stable IRIs in vocab/. Not a medical device; not certified as a speech-generating device (SGD) for insurance funding (see SPEC §11).

Licence

• Reference code (aac-rs/): Apache-2.0 — see LICENSE.
• Specification text (SPEC.md, spec/, vocab/): CC-BY-4.0 — see LICENSE-SPEC.