Qualified Piece Identifier (QPI) Specification

Version: 1.0.0
Author: Sashité
Published: June 23, 2025
License: MIT License

Overview

Qualified Piece Identifier (QPI) provides a rule-agnostic format for identifying game pieces in abstract strategy board games by combining Style Identifier Notation (SIN) and Piece Identifier Notation (PIN) with a colon separator.

QPI represents all four fundamental piece attributes:

Type → PIN component (ASCII letter choice)
Side → PIN component (letter case)
State → PIN component (optional prefix modifier)
Style → SIN component (style identifier)

Unlike Extended Piece Identifier Notation (EPIN) which uses derivation markers, QPI explicitly names the style for unambiguous identification.

Terminology

For complete definitions of terms used in this document, see the Glossary.

Format Specification

Structure

<sin>:<pin>

Grammar (BNF)

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

<uppercase-qpi> ::= <uppercase-letter> <colon> <uppercase-pin>
<lowercase-qpi> ::= <lowercase-letter> <colon> <lowercase-pin>

<colon> ::= ":"

<uppercase-pin> ::= <uppercase-letter> | <state-modifier> <uppercase-letter>
<lowercase-pin> ::= <lowercase-letter> | <state-modifier> <lowercase-letter>

<state-modifier> ::= "+" | "-"

<uppercase-letter> ::= "A" | "B" | "C" | ... | "Z"
<lowercase-letter> ::= "a" | "b" | "c" | ... | "z"

Regular Expression

\A([A-Z]:[-+]?[A-Z]|[a-z]:[-+]?[a-z])\z

Piece Attribute Mapping

QPI encodes piece attributes by combining SIN and PIN information:

Piece Attribute	QPI Encoding	Examples
Type	PIN letter choice	`C:K` = King, `C:P` = Pawn
Side	PIN case	`C:K` = First player, `C:k` = Second player
State	PIN prefix modifier	`S:+P` = Enhanced, `C:-P` = Diminished
Style	SIN identifier	`C:K` = Chess style, `S:K` = Shōgi style

Important: The SIN and PIN components encode their respective attributes independently. The SIN component indicates which style governs the piece, while the PIN component handles type, side, and state according to PIN specification rules.

Component Relationship

Independent Encoding

QPI treats SIN and PIN as independent components connected by a colon separator:

SIN component: Identifies the style using single ASCII letter
PIN component: Identifies type, side, and state using PIN format
Separator: Colon (:) provides clear delimitation

Cross-Reference Constraint

While the components are syntactically independent, there is a semantic constraint: the style identified by the SIN component must be associated with the same player as indicated by the PIN case. This ensures consistency between style assignment and piece ownership.

Valid combinations:

C:K - Chess style with first player king
c:k - Chess style with second player king

Invalid semantic combinations (syntactically valid but semantically inconsistent):

C:k - Chess style (first player) with second player piece
c:K - Chess style (second player) with first player piece

Design Properties

Rule-agnostic: Independent of specific game mechanics
Complete identification: Explicit representation of all four piece attributes
Cross-style support: Enables multi-tradition gaming environments
Component clarity: Clear separation between style context and piece identity
Independent validation: Each component can be validated according to its own specification
Comprehensive attribute representation: Direct implementation of Sashité piece attributes

Examples

See QPI Examples for practical implementation guidance.

Reference Implementations

Ruby

QPI.rb – Reference implementation of the Qualified Piece Identifier specification.