Pushout

A graph rewriting library built on petgraph, providing:

• VF2 subgraph isomorphism for pattern matching
• DPO (Double Pushout) algebraic graph rewriting with rule definitions
• Neo4j JSON import into petgraph::Graph
• Cypher export of DPO rules for Neo4j execution

Crate: pushout · License: Apache-2.0

Features

1. Pattern Matching (src/algorithms/vf2.rs)

   • match_subgraphs & has_subgraph via the VF2 algorithm

2. Graph Rewriting (src/transformation/)

   • Define DPO rules with LHS, Interface (K), RHS graphs
   • apply_once, apply_rules, apply_exhaustive
   • RuleBuilder for ergonomic rule construction

3. I/O

   • load_neo4j_graph(json: &str) to parse Neo4j JSON exports
   • export_rule_to_cypher & save_rule_as_cypher for Cypher queries

Future work: RDF/SPARQL support via optional graphdb feature.

Getting Started

Add to your Cargo.toml:

[dependencies]
pushout = "0.1.1"
petgraph = "0.8.1"
serde = { version = "1.0", features = ["derive"] }
thiserror = "2.0.12"

Then in your code:

use pushout::api::{
    match_subgraphs, has_subgraph,
    apply_rule, apply_rules,
    RuleBuilder,
    load_neo4j_graph, export_rule_to_cypher,
};
use petgraph::graph::Graph;

// 1. Load a Neo4j JSON export
let json = std::fs::read_to_string("graph.json")?;
let host: Graph<_, String> = load_neo4j_graph(&json)?;

// 2. Build a DPO rule
let rule = RuleBuilder::new()
    .lhs(pattern_graph)
    .interface(interface_graph)
    .rhs(replacement_graph)
    .l2k(l2k_morphism)
    .k2r(k2r_morphism)
    .build();

// 3. Apply the rule
let result = apply_rule(&host, &rule).unwrap_or(host.clone());

// 4. Export to Cypher
let cy = export_rule_to_cypher(&rule);
std::fs::write("rule.cypher", cy)?;

License

This project is licensed under Apache License, Version 2.0