Piece Name Notation (PNN) Specification

Version: 1.0.0 Author: Sashité Published: May 1, 2025 License: MIT License

Overview

Piece Name Notation (PNN) defines a consistent and rule-agnostic format for representing pieces in abstract strategy board games. This specification establishes a standardized way to identify and represent pieces independent of any specific game rules or mechanics.

Properties

PNN is rule-agnostic and does not encode legality, validity, or game-specific conditions.
PNN provides a canonical representation, ensuring that equivalent pieces yield identical strings.
PNN allows for state modifiers to express special conditions without compromising rule neutrality.

Constraints

PNN supports exactly two players.
Players are assigned distinct casing: uppercase letters (A-Z) represent pieces of the player who moves first in the initial position; lowercase letters (a-z) represent the second player.
A maximum of 26 unique piece types per player is allowed, as identifiers must use single letters (a-z or A-Z).
Modifiers can only be applied to pieces on the board, as they express state information. Pieces held off the board (e.g., pieces in hand or captured pieces) must never include modifiers; only the base letter identifier is used.

Format

A piece is represented by an identifier composed of a single ASCII letter, optionally modified by prefixes and/or suffixes.

Piece Identifier Structure

[<prefix>]<letter>[<suffix>]

Where:

<letter> is a single ASCII letter (a-z or A-Z).
<prefix> is an optional modifier preceding the letter (+ or -).
<suffix> is an optional modifier following the letter (').

Modifiers

Modifiers provide a mechanism to express the state of pieces on the board without compromising the rule-agnostic nature of the notation.

Modifier Meanings

Modifier	Meaning
`+`	Enhanced state
`-`	Diminished state
`'`	Intermediate state

Modifier Application Rules

Modifiers are strictly optional.
A piece may have a prefix, a suffix, both, or neither.
Modifiers do not change the fundamental identity of the piece but only express variations in state.
Modifiers only apply to pieces on the board. Pieces off the board (in hand, captured) must use the plain letter only.

Formal Grammar (BNF)

<piece> ::= <letter>
         | <prefix> <letter>
         | <letter> <suffix>
         | <prefix> <letter> <suffix>

<prefix> ::= "+" | "-"
<suffix> ::= "'"

<letter> ::= <letter-lowercase> | <letter-uppercase>

<letter-lowercase> ::= "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j"
                    | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t"
                    | "u" | "v" | "w" | "x" | "y" | "z"

<letter-uppercase> ::= "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J"
                    | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T"
                    | "U" | "V" | "W" | "X" | "Y" | "Z"

JSON Schema

The following JSON Schema defines the validation pattern for a PNN piece string:

{
  "type": "string",
  "pattern": "^[-+]?[a-zA-Z]'?$"
}

PNN Implementations

This section lists available libraries and tools that implement the PNN specification, allowing developers to easily integrate this format into their applications.

Ruby

Pnn.rb – Implementation of the Piece Name Notation specification for Ruby.