README.md

GDL - Graph Definition Language

Inspired by the popular graph query language Cypher, which is implemented in Neo4j, I started developing an ANTLR grammar to define property graphs. I added the concept of subgraphs into the language to support multiple, possible overlapping property graphs in one database.

For me, this project is a way to learn more about ANTLR and context-free grammars. Furthermore, GDL is used for unit testing and graph definition in Gradoop, a framework for distributed graph analytics.

The project contains the grammar and a listener implementation which transforms GDL scripts into property graph model elements (i.e. graphs, vertices and edges).

Data model

The data model contains three elements: graphs, vertices and edges. Any element has an optional label and can have multiple attributes in the form of key-value pairs. Vertices and edges may be contained in an arbitrary number of graphs including zero graphs. Edges are binary and directed.

Language Examples

Define a vertex:

()

Define a vertex and assign it to variable alice:

(alice)

Define a vertex with label User:

(:User)

Define a vertex with label User, assign it to variable alice and give it some properties:

(alice:User {name : "Alice", age : 23})

Property values can also be null:

(alice:User {name : "Alice", age : 23, city : NULL})

Numeric property values can have specific data types:

(alice:User {name : "Alice", age : 23L, height : 1.82f, weight : 42.7d})

Define an outgoing edge:

(alice)-->()

Define an incoming edge:

(alice)<--()

Define an edge with label knows, assign it to variable e1 and give it some properties:

(alice)-[e1:knows {since : 2014}]->(bob)

Define multiple outgoing edges from the same source vertex (i.e. alice):

(alice)-[e1:knows {since : 2014}]->(bob)
(alice)-[e2:knows {since : 2013}]->(eve)

Define paths (four vertices and three edges are created):

()-->()<--()-->()

Define a graph with one vertex (graphs can be empty):

[()]

Define a graph and assign it to variable g:

g[()]

Define a graph with label Community:

:Community[()]

Define a graph with label Community, assign it to variable g and give it some properties:

g:Community {title : "Graphs", memberCount : 42}[()]

Define mixed path and graph statements (elements in the paths don't belong to a specific graph):

()-->()<--()-->()
[()]

Define a fragmented graph with variable reuse:

g[(a)-->()]
g[(a)-->(b)]
g[(b)-->(c)]

Define three graphs with overlapping vertex sets (e.g. alice is in g1 and g2):

g1:Community {title : "Graphs", memberCount : 23}[
    (alice:User)
    (bob:User)
    (eve:User)
]
g2:Community {title : "Databases", memberCount : 42}[
    (alice)
]
g2:Community {title : "Hadoop", memberCount : 31}[
    (bob)
    (eve)
]

Define three graphs with overlapping vertex and edge sets (e is in g1 and g2):

g1:Community {title : "Graphs", memberCount : 23}[
    (alice:User)-[:knows]->(bob:User),
    (bob)-[e:knows]->(eve:User),
    (eve)
]
g2:Community {title : "Databases", memberCount : 42}[
    (alice)
]
g2:Community {title : "Hadoop", memberCount : 31}[
    (bob)-[e]->(eve)
]

Query Expressions

As part of his thesis, Max extended the grammar to support MATCH .. WHERE .. statements analogous to Cypher. Besides defining a graph it is now also possible to formulate a query including patterns, variable length paths and predicates:

MATCH (alice:Person)-[:knows]->(bob:Person)-[:knows*2..2]->(eve:Person)
WHERE (alice.name = "Alice" AND bob.name = "Bob") 
OR (alice.age > bob.age)
OR (alice.age > eve.age)

Note that queries always start with the MATCH keyword optionally followed by one or more WHERE clauses.

Usage examples

Add dependency to your maven project:

<dependency>
    <groupId>com.github.s1ck</groupId>
    <artifactId>gdl</artifactId>
    <version>0.3</version>
</dependency>

Create a database from a GDL string:

GDLHandler handler = new GDLHandler.Builder().buildFromString("g[(alice)-[e1:knows {since : 2014}]->(bob)]");

for (Vertex v : handler.getVertices()) {
    // do something
}

// access elements by variable
Graph g = handler.getGraphCache().get("g");
Vertex alice = handler.getVertexCache().get("alice");
Edge e = handler.getEdgeCache().get("e1");

Read predicates from a Cypher query:

GDLHandler handler = new GDLHandler.Builder().buildFromString("MATCH (a:Person)-[e:knows]->(b:Person) WHERE a.age > b.age");

// prints (((a.age > b.age AND a.__label__ = Person) AND b.__label__ = Person) AND e.__label__ = knows)
handler.getPredicates().ifPresent(System.out::println);

Create a database from an InputStream or an input file:

GDLHandler handler1 = new GDLHandler.Builder().buildFromStream(stream);
GDLHandler handler2 = new GDLHandler.Builder().buildFromFile(fileName);

Append data to a given handler:

GDLHandler handler = new GDLHandler.Builder().buildFromString("g[(alice)-[e1:knows {since : 2014}]->(bob)]");

handler.append("g[(alice)-[:knows]->(eve)]");

License

Licensed under the Apache License, Version 2.0.