021-snake-game/docs/dictionary.md

# Domain Dictionary: Snake Game (Day 21)

## Metadata
| Key | Value |
| --- | --- |
| ID | DICT-001 |
| CrossReference | [BC-001], [SA-001] |
| Language | en |
| Domain | it |

## Version History
| Date | Status | Author | Reviewer | Change | Commit |
| --- | --- | --- | --- | --- | --- |
| 2026-10-08 | Accepted | Jens Tirsvad Nielsen | S01 | Initial version, reviewed in RC-003 (Go) | pending |

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## Purpose and Scope

Maps each Product Owner (PO) term to its professional information technology (IT) term. PO language: `en` (domain `it`), from the registry's `Languages` section. The PO terms are the words of the lectures of days 20 and 21 as the planning documents use them; the IT terms are the names in the code. The dictionary covers the vocabulary of the game; it exists so that the planning documents use one word for one thing and so that S02 can find the lectures' names in the code. It is adopted from the dictionary of the day-20 repository and gains the terms refresh and inheritance, which the day-21 lectures introduce.

## Dictionary

| PO term | Language | IT term | Definition | Used as PO term in | Used as IT term in |
| --- | --- | --- | --- | --- | --- |
| window | en | Tk window | The desktop window that holds the screen and is opened when the game starts. | BC, SA, PP, MIL | PY |
| screen | en | `Screen` | The drawing area that the game sets up (size, colour, title) and on which the snake is shown. | BC, SA, PP, MIL | PY |
| snake | en | `Snake` | The creature the player steers, made of segments. | BC, SA, PP, MIL | PY |
| segment | en | `Turtle` | One white square of the snake. | BC, SA, PP, MIL | PY |
| head | en | `head` | The first segment, which leads the snake and is turned by the arrow keys. | BC, SA, PP, MIL | PY |
| tail | en | `segments[1:]` | Every segment behind the head; the game is over when the head touches one of them. | BC, SA, PP, MIL | PY |
| body | en | `segments` | All segments of the snake, the head included, in order, the head first. | BC, SA, PP, MIL | PY |
| starting position | en | `STARTING_POSITIONS` | One of the three places at which a segment is drawn when the game starts. | BC, MIL | PY |
| move | en | `move` | One pass in which each segment takes the place of the one before it and the head goes forward by the move distance. | BC, SA, PP, MIL | PY |
| move distance | en | `MOVE_DISTANCE` | How far the head goes in one move, 20 pixels. | BC, MIL | PY |
| direction | en | `heading` | The way the head points: up, down, left or right. | BC, SA, PP, MIL | PY |
| reversal | en | opposite heading | A turn by 180 degrees, so that the head would run into the segment behind it. | BC, SA, PP, MIL | PY |
| arrow key | en | key name `"Up"`, `"Down"`, `"Left"`, `"Right"` | One of the four keys with which the player turns the head. | BC, SA, PP, MIL | PY |
| key binding | en | `onkey` | The link between an arrow key and the method that turns the head. | BC, PP, MIL | PY |
| animation loop | en | `while game_is_on` loop | The loop that refreshes the screen, waits and makes one move, again and again. | BC, PP, MIL | PY |
| refresh delay | en | `REFRESH_DELAY_SECONDS` | The wait between two moves, 0.1 seconds. | BC, MIL | PY |
| food | en | `Food` | The small blue circle that the snake eats; it is shown at a random place. | BC, SA, PP, MIL | PY |
| refresh | en | `refresh` | The food moves to a new random place; it happens when the game starts and every time the food is eaten. | BC, SA, MIL | PY |
| eat | en | `FOOD_COLLISION_DISTANCE` | The head comes closer to the food than this distance, which makes the snake grow and the score rise. | BC, MIL | PY |
| grow | en | `extend` | The snake gets one more segment, at the place where its last segment is. | BC, SA, MIL | PY |
| score | en | `score` | The number of foods the snake has eaten in this game. | BC, SA, PP, MIL | PY |
| scoreboard | en | `Scoreboard` | The text at the top of the screen that shows the score. | BC, SA, MIL | PY |
| wall | en | `WALL_LIMIT` | The line on every side of the playing field, 280 pixels from the centre; the head must stay inside it and the food is shown inside it. | BC, SA, PP, MIL | PY |
| touch | en | `TAIL_COLLISION_DISTANCE` | The head comes closer to a segment of the tail than this distance. | BC, MIL | PY |
| game over | en | `game_over` | The end of the game, shown with the text GAME OVER, when the head passes the wall or touches the tail. | BC, SA, PP, MIL | PY |
| inheritance | en | subclass of `Turtle` | A class takes over the attributes and methods of another class; `Food` and `Scoreboard` take over those of `Turtle`. | BC, SA, MIL | PY |

## Rules

- The Business Case, Stakeholder Analysis, Project Plan and milestones use the PO term; the source code and its tests use the IT term. The other design artifacts (Domain Model, Operation Contract, Sequence Diagram, Design Class Diagram, ERD) do not exist in this project.
- One IT term per PO term and one PO term per IT term; no synonyms.
- The planning documents use British spelling (colour, centre); identifiers such as `color` follow the `turtle` module and the lectures.
- A code identifier written in backticks in a planning document is an IT term and is allowed there.
- "Step" is not a PO term of the game. In the planning documents it means a step of the project (a task, a milestone), never a move of the snake.
- "Base" is not a PO term of the game. In the planning documents it means the finished `main` of the day-20 repository that this project adopts, never a part of the game.

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[BC-001]: ./business-case.md
[SA-001]: ./stakeholder-analysis.md