Adjacency

Adjacency is a structure used to specify how many objects of a particular kind can be accepted within a relation. It is a fundamental unit within the adjacency specification.

Representation

The Adjacency structure is defined as follows:

#![allow(unused)]
fn main() {
pub struct Adjacency {
    kind: u64,
    deg_min: u32,
    deg_max: u32,
}
}

Field Descriptions

Encoding

A single Adjacency structure can be encoded into a u128 for compact representation:

#![allow(unused)]
fn main() {
let encoded = (u128(adjacency.kind) << 64)
            | (u128(adjacency.deg_min) << 32)
            | u128(adjacency.deg_max);
}

Adjacency Specification

An adjacency specification defines the set of adjacencies that a relation supports.

Ascending Order

Adjacencies must be listed in ascending order based on the kind field.

Special Kind Values

Two special kind values have particular meanings:

• u64::MIN (0): Represents "any," meaning any kind not explicitly mentioned.
• u64::MAX (2^64 - 1): Represents "total," indicating the total number of objects that can be accepted in the relation.

The "any" kind must always be listed first, and the "total" kind must be last, if present.

Encoding

An adjacency specification can be encoded into a series of Bytes32 values.

Each Bytes32 can hold two Adjacency structures. If the number of adjacencies is odd, the remaining space in the final Bytes32 is padded with zeros.