BLUEPRINT

Chapter 3: Entities and Relationships

This chapter describes the semantics, ownership rules, and mutual relationships of the four kinds of core entities in the FayID system.

Four Kinds of Core Entities

Human ID — A Natural Person's Root Identity

A Human ID is a natural person's unique root identity within the FayID system. It has the following characteristics:

Derived from a key pair, paired with a Mnemonic
Globally unique; the same Mnemonic deterministically derives the same Human ID
The "ownership anchor" of every other entity — iFay IDs are bound to it and coFay IDs may be owned by it
Must not appear in plaintext in public communication (a privacy hard constraint)

The Human ID is the root; every other identity grows from it.

iFay ID — Digital Persona

An iFay ID identifies a single iFay digital persona. Core rules:

Each iFay ID must be bound to exactly one Human ID (many-to-one)
A single Human ID may bind multiple iFay IDs (one person, many personas)
A single iFay ID may not be bound to multiple Human IDs (bindings do not overlap)
Supports revocation (irreversible)

coFay ID — Public Role

A coFay ID identifies a public-facing shared role. Core rules:

Each coFay ID has exactly one owner at any moment
The owner may be either a Human ID or an Organization ID (one or the other)
A single Human ID or Organization ID may own multiple coFay IDs
A Verification Code is issued together with the coFay ID at creation time
Supports revocation (irreversible)

Organization ID — Organization Identifier

An Organization ID identifies an organizational entity. Core rules:

Used publicly in plaintext string form
Does not derive a Dynamic Code (no privacy protection needed)
May own multiple coFay IDs
The Resolver can return the corresponding organization entity directly from the Organization ID string, with no additional credential required

Ownership and Binding Relationships

Relationships at a Glance

Relationship	Cardinality	Description
Human ID → iFay ID	one-to-many	One person may have many digital personas
iFay ID → Human ID	many-to-one	Each persona belongs to exactly one person
Human ID → coFay ID	one-to-many	One person may own many public roles
Organization ID → coFay ID	one-to-many	One organization may own many public roles
coFay ID → owner	one-to-one	Each role has exactly one owner at any moment
Human ID → Dynamic Code	one-to-many	Each request generates a new Dynamic Code
coFay ID → Verification Code	one-to-one (versioned)	Each rotation produces a new version; the previous version becomes invalid immediately

Entity Relationship Diagram

erDiagram
  HUMAN_ID ||--o{ IFAY_ID : "owns (1:N)"
  HUMAN_ID ||--o{ COFAY_ID : "owns (HUMAN kind)"
  ORGANIZATION_ID ||--o{ COFAY_ID : "owns (ORGANIZATION kind)"
  HUMAN_ID ||--o{ DYNAMIC_CODE : "derives"
  COFAY_ID ||--|| VERIFICATION_CODE : "1:1 (versioned)"
  HUMAN_ID ||--o{ AUTHORIZATION_GRANT : "target (Human variant)"
  IFAY_ID ||--o{ AUTHORIZATION_GRANT : "target (iFay variant)"

Key Invariants

The following invariants must hold in every legal state of the system:

iFay ID binding uniqueness: any iFay ID is bound to exactly one Human ID at any moment, and that binding is immutable for the iFay ID's entire lifetime.
coFay ID ownership uniqueness: any coFay ID has exactly one owner (a Human ID or an Organization ID) at any moment, and the OwnerKind and ownerRef stay mutually consistent.
Global identifier uniqueness: Human IDs, iFay IDs, coFay IDs, and Organization IDs are globally unique within their respective namespaces; the type prefix naturally avoids cross-type collisions.
Revocation monotonicity: once an iFay ID or coFay ID is marked revoked, that state is irreversible.

These invariants correspond to Property P1 (identity-creation uniqueness + ownership consistency) and Property P8 (revocation monotonicity) in the design document.

Ownership Queries

The Resolver provides the following ownership-query capabilities:

Given an iFay ID → returns the unique Human ID it belongs to (as an opaqueRef, never exposing the Human ID in plaintext)
Given a coFay ID → returns the OwnerKind (Human / Organization) and the owner identifier
Given a Human ID + ownership proof → returns the list of iFay IDs owned by that Human ID

Note: querying the list of iFay IDs owned by a Human ID must be gated by ownership proof; without it, the Resolver refuses to return results. This is part of the privacy protection.