# RDF Isomorphism

Determines if two RDF graphs are isomorphic, i.e., if two RDF graphs are equal while ignoring quad order and ignoring non-equal blank node labels between the graphs.

This package is can be useful within unit/spec tests.

This library accepts RDFJS-compliant quads.

## Usage

The following examples assume the following imports:

```
import { DataFactory } from "rdf-data-factory"; // External library
import { isomorphic } from "rdf-isomorphic";
const factory = new DataFactory();
```

### Check if two graphs are isomorphic

```
const graphA = [
factory.quad(
factory.blankNode('s1'),
factory.namedNode('p'),
factory.blankNode('o1'),
),
];
const graphB = [
factory.quad(
factory.blankNode('s2'),
factory.namedNode('p'),
factory.blankNode('o2'),
),
];
isomorphic(graphA, graphB); // Outputs true
```

**not** isomorphic

Check if two graphs are ```
const graphA = [
factory.quad(
factory.blankNode('s1'),
factory.namedNode('p1'),
factory.blankNode('o1'),
),
];
const graphB = [
factory.quad(
factory.blankNode('s2'),
factory.namedNode('p2'),
factory.blankNode('o2'),
),
];
isomorphic(graphA, graphB); // Outputs false
```

### Check if two graphs with nested quads are isomorphic

```
const graphA = [
factory.quad(
factory.quad(
factory.blankNode('sInner'),
factory.namedNode('pInner'),
factory.blankNode('o1'),
),
factory.namedNode('pOuter'),
factory.namedNode('oOuter'),
)
];
const graphB = [
factory.quad(
factory.quad(
factory.blankNode('sInner'),
factory.namedNode('pInner'),
factory.blankNode('o2'),
),
factory.namedNode('pOuter'),
factory.namedNode('oOuter'),
)
];
isomorphic(graphA, graphB); // Outputs true
```

## Algorithm

This algorithm is based on the RDF isomorphism checker in RDF.rb, which in its turn is based on the algorithm described by Jeremy Carrol.

In summary, the algorithm generates a hash for each blank node based on the connected resources. These hashes are then compared between the two given graphs, and a bijection is attempted to be created. If no such bijection can be found, then the graphs are considered non-isomorphic.

The implementation of this package is inspired by the Ruby RDF::Isomorphic gem.

The algorithm has been adapted to work this nested quads by Ruben Taelman.

## License

This software is written by Ruben Taelman.

This code is released under the MIT license.