Struct FInstanceHom 

pub struct FInstanceHom {
    pub row_maps: HashMap<String, Vec<usize>>,
}

A homomorphism between two set-valued functor instances of the same schema.

For each table (schema vertex), a row map sends each row index of the domain to a row index of the codomain. A well-formed homomorphism preserves foreign keys; check verifies this.

Fields

row_maps: HashMap<String, Vec<usize>>

Per-table row maps: table name to a vector indexed by domain row index, whose entry is the corresponding codomain row index.

Implementations

impl FInstanceHom

pub const fn new(row_maps: HashMap<String, Vec<usize>>) -> Self

Build a homomorphism from explicit per-table row maps.

pub fn identity(instance: &FInstance) -> Self

The identity homomorphism on instance (each row maps to itself).

pub fn check(&self, dom: &FInstance, cod: &FInstance) -> Result<(), HomError>

Verify that this homomorphism from dom to cod preserves the relational structure.

Checks totality (every domain table has a row map of the right length, present in the codomain, whose entries are in range) and foreign-key naturality (each domain foreign-key pair maps to a codomain pair).

Errors

Returns the first HomError encountered.

pub fn compose(&self, other: &Self) -> Result<Self, HomError>

Compose two homomorphisms: self from A to B followed by other from B to C.

Errors

Returns HomError::ComposeRowMismatch if the tables or row indices do not line up.

pub fn is_isomorphism(&self, dom: &FInstance, cod: &FInstance) -> bool

Returns true iff this homomorphism from dom to cod is an isomorphism: each row map is a bijection and the inverse preserves foreign keys.

Trait Implementations

impl Clone for FInstanceHom

fn clone(&self) -> FInstanceHom

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FInstanceHom

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for FInstanceHom

fn default() -> FInstanceHom

Returns the “default value” for a type.

impl Eq for FInstanceHom

impl PartialEq for FInstanceHom

fn eq(&self, other: &FInstanceHom) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for FInstanceHom