open-standards/aac/spec/board.md

AAC sub-spec — The board data model

Normative refinement of SPEC §2. Reference: aac_core::{Board, Cell, GridLayout, GridPosition, CellContent, CellAction, BoardType}.

A board is a person's communication surface. It is a small, text-like document — artwork is referenced, not embedded (§4) — so a voice travels cheaply between devices and implementations.

Board = (id: BoardId, name: String, board_type: BoardType,
         layout: GridLayout, cells: [Cell])
Cell  = (id: CellId, position: GridPosition, content: CellContent,
         action: CellAction, style: CellStyle, frequency: u64, locked: bool)

1. Identity — id: BoardId, id: CellId

Both are UUIDs, stable for the life of the structure. A BoardId is the target of a Navigate action, so it is also the edge label of the board graph (§5). Two openings of the same logical board MUST present the same BoardId and the same set of CellIds.

2. Board type — board_type

One of Grid (a symbol grid), VisualScene (photo-based with hotspots, for emerging communicators), Keyboard (text input, for literate users), Hybrid (mixed symbol + text), QuickAccess (high-frequency phrases — the home board). The type is a rendering hint and a vocabulary-strategy marker; it MUST NOT change a cell's position semantics (§3 of SPEC).

3. Layout — layout: GridLayout { rows: u16, cols: u16 }

The grid dimensions. capacity = rows × cols is the maximum number of non-overlapping cells. A board MAY hold fewer cells than its capacity; absent positions render as empty grid (distinct from a Blank cell, which is an explicit, addressable reservation — see §5).

4. Position — position: GridPosition { row: u16, col: u16 }

0-indexed. A position is assigned once and is immutable for the life of the cell (motor stability — see motor_stability.md). No two cells on a board MAY share a position.

5. Content — content: CellContent

One of:

• Symbol { symbol_id, label } — a symbol referenced by registry id plus its text label. The label MUST survive round-trip even where the artwork cannot be rendered ([../SPEC.md §4]).
• Text(String) — plain text, for keyboard boards and literate users.
• Photo { image_ref, label } — a referenced image with a label, for visual scenes.
• Blank — an intentional, addressable empty. A Blank reserves its position to preserve the surrounding motor grid and MUST NOT be elided on round-trip.

6. Action — action: CellAction

What activation does: Speak(text), Navigate(BoardId), Modifier(GrammarModifier), Backspace, Clear, Predict, SpeakAll, Buffer(text). Navigate edges the board graph; Modifier applies a grammatical transform (Plural, PastTense, PresentProgressive, FutureTense, Possessive, Negation, Question, Pronoun(name)) to the message bar; Buffer adds to the message bar without speaking.

The board graph is the source of truth; a grid is one projection of it. A conforming editor MUST keep the Navigate edges referentially intact: deleting a board MUST report, not silently break, any cell that navigates to it.

7. Canonicality

A board serializes to the canonical interchange form of SPEC §7. Round-trip MUST preserve every position, content, action, and symbol_id byte-for-byte. Conformance suite C4 pins the wire round-trip; the published vectors live in ../conformance/v1/.