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Neo4j

Neo4j is a graph database management system developed by Neo4j, Inc.

The data elements Neo4j stores are nodes, edges connecting them, and attributes of nodes and edges. Described by its developers as an ACID-compliant transactional database with native graph storage and processing, Neo4j is available in a non-open-source “community edition” licensed with a modification of the GNU General Public License, with online backup and high availability extensions licensed under a closed-source commercial license. Neo also licenses Neo4j with these extensions under closed-source commercial terms.

This notebook shows how to use LLMs to provide a natural language interface to a graph database you can query with the Cypher query language.

Cypher is a declarative graph query language that allows for expressive and efficient data querying in a property graph.

Setting up​

You will need to have a running Neo4j instance. One option is to create a free Neo4j database instance in their Aura cloud service. You can also run the database locally using the Neo4j Desktop application, or running a docker container. You can run a local docker container by running the executing the following script:

docker run \
    --name neo4j \
    -p 7474:7474 -p 7687:7687 \
    -d \
    -e NEO4J_AUTH=neo4j/password \
    -e NEO4J_PLUGINS=\[\"apoc\"\]  \
    neo4j:latest

If you are using the docker container, you need to wait a couple of second for the database to start.

from langchain.chains import GraphCypherQAChain
from langchain_community.graphs import Neo4jGraph
from langchain_openai import ChatOpenAI
graph = Neo4jGraph(url="bolt://localhost:7687", username="neo4j", password="password")

Seeding the database​

Assuming your database is empty, you can populate it using Cypher query language. The following Cypher statement is idempotent, which means the database information will be the same if you run it one or multiple times.

graph.query(
    """
MERGE (m:Movie {name:"Top Gun", runtime: 120})
WITH m
UNWIND ["Tom Cruise", "Val Kilmer", "Anthony Edwards", "Meg Ryan"] AS actor
MERGE (a:Actor {name:actor})
MERGE (a)-[:ACTED_IN]->(m)
"""
)
[]

Refresh graph schema information​

If the schema of database changes, you can refresh the schema information needed to generate Cypher statements.

graph.refresh_schema()
print(graph.schema)
Node properties:
Movie {runtime: INTEGER, name: STRING}
Actor {name: STRING}
Relationship properties:

The relationships:
(:Actor)-[:ACTED_IN]->(:Movie)

Enhanced schema information​

Choosing the enhanced schema version enables the system to automatically scan for example values within the databases and calculate some distribution metrics. For example, if a node property has less than 10 distinct values, we return all possible values in the schema. Otherwise, return only a single example value per node and relationship property.

enhanced_graph = Neo4jGraph(
    url="bolt://localhost:7687",
    username="neo4j",
    password="password",
    enhanced_schema=True,
)
print(enhanced_graph.schema)
Node properties:
- **Movie**
  - `runtime: INTEGER` Min: 120, Max: 120
  - `name: STRING` Available options: ['Top Gun']
- **Actor**
  - `name: STRING` Available options: ['Tom Cruise', 'Val Kilmer', 'Anthony Edwards', 'Meg Ryan']
Relationship properties:

The relationships:
(:Actor)-[:ACTED_IN]->(:Movie)

Querying the graph​

We can now use the graph cypher QA chain to ask question of the graph

chain = GraphCypherQAChain.from_llm(
    ChatOpenAI(temperature=0), graph=graph, verbose=True
)
chain.invoke({"query": "Who played in Top Gun?"})


> Entering new GraphCypherQAChain chain...
Generated Cypher:
MATCH (a:Actor)-[:ACTED_IN]->(m:Movie)
WHERE m.name = 'Top Gun'
RETURN a.name
Full Context:
[{'a.name': 'Anthony Edwards'}, {'a.name': 'Meg Ryan'}, {'a.name': 'Val Kilmer'}, {'a.name': 'Tom Cruise'}]

> Finished chain.
{'query': 'Who played in Top Gun?',
 'result': 'Anthony Edwards, Meg Ryan, Val Kilmer, Tom Cruise played in Top Gun.'}

Limit the number of results​

You can limit the number of results from the Cypher QA Chain using the top_k parameter. The default is 10.

chain = GraphCypherQAChain.from_llm(
    ChatOpenAI(temperature=0), graph=graph, verbose=True, top_k=2
)
chain.invoke({"query": "Who played in Top Gun?"})


> Entering new GraphCypherQAChain chain...
Generated Cypher:
MATCH (a:Actor)-[:ACTED_IN]->(m:Movie)
WHERE m.name = 'Top Gun'
RETURN a.name
Full Context:
[{'a.name': 'Anthony Edwards'}, {'a.name': 'Meg Ryan'}]

> Finished chain.
{'query': 'Who played in Top Gun?',
 'result': 'Anthony Edwards, Meg Ryan played in Top Gun.'}

Return intermediate results​

You can return intermediate steps from the Cypher QA Chain using the return_intermediate_steps parameter

chain = GraphCypherQAChain.from_llm(
    ChatOpenAI(temperature=0), graph=graph, verbose=True, return_intermediate_steps=True
)
result = chain.invoke({"query": "Who played in Top Gun?"})
print(f"Intermediate steps: {result['intermediate_steps']}")
print(f"Final answer: {result['result']}")


> Entering new GraphCypherQAChain chain...
Generated Cypher:
MATCH (a:Actor)-[:ACTED_IN]->(m:Movie)
WHERE m.name = 'Top Gun'
RETURN a.name
Full Context:
[{'a.name': 'Anthony Edwards'}, {'a.name': 'Meg Ryan'}, {'a.name': 'Val Kilmer'}, {'a.name': 'Tom Cruise'}]

> Finished chain.
Intermediate steps: [{'query': "MATCH (a:Actor)-[:ACTED_IN]->(m:Movie)\nWHERE m.name = 'Top Gun'\nRETURN a.name"}, {'context': [{'a.name': 'Anthony Edwards'}, {'a.name': 'Meg Ryan'}, {'a.name': 'Val Kilmer'}, {'a.name': 'Tom Cruise'}]}]
Final answer: Anthony Edwards, Meg Ryan, Val Kilmer, Tom Cruise played in Top Gun.

Return direct results​

You can return direct results from the Cypher QA Chain using the return_direct parameter

chain = GraphCypherQAChain.from_llm(
    ChatOpenAI(temperature=0), graph=graph, verbose=True, return_direct=True
)
chain.invoke({"query": "Who played in Top Gun?"})


> Entering new GraphCypherQAChain chain...
Generated Cypher:
MATCH (a:Actor)-[:ACTED_IN]->(m:Movie)
WHERE m.name = 'Top Gun'
RETURN a.name

> Finished chain.
{'query': 'Who played in Top Gun?',
 'result': [{'a.name': 'Anthony Edwards'},
  {'a.name': 'Meg Ryan'},
  {'a.name': 'Val Kilmer'},
  {'a.name': 'Tom Cruise'}]}

Add examples in the Cypher generation prompt​

You can define the Cypher statement you want the LLM to generate for particular questions

from langchain_core.prompts.prompt import PromptTemplate

CYPHER_GENERATION_TEMPLATE = """Task:Generate Cypher statement to query a graph database.
Instructions:
Use only the provided relationship types and properties in the schema.
Do not use any other relationship types or properties that are not provided.
Schema:
{schema}
Note: Do not include any explanations or apologies in your responses.
Do not respond to any questions that might ask anything else than for you to construct a Cypher statement.
Do not include any text except the generated Cypher statement.
Examples: Here are a few examples of generated Cypher statements for particular questions:
# How many people played in Top Gun?
MATCH (m:Movie {{title:"Top Gun"}})<-[:ACTED_IN]-()
RETURN count(*) AS numberOfActors

The question is:
{question}"""

CYPHER_GENERATION_PROMPT = PromptTemplate(
    input_variables=["schema", "question"], template=CYPHER_GENERATION_TEMPLATE
)

chain = GraphCypherQAChain.from_llm(
    ChatOpenAI(temperature=0),
    graph=graph,
    verbose=True,
    cypher_prompt=CYPHER_GENERATION_PROMPT,
)

API Reference:

chain.invoke({"query": "How many people played in Top Gun?"})


> Entering new GraphCypherQAChain chain...
Generated Cypher:
MATCH (:Movie {name:"Top Gun"})<-[:ACTED_IN]-()
RETURN count(*) AS numberOfActors
Full Context:
[{'numberOfActors': 4}]

> Finished chain.
{'query': 'How many people played in Top Gun?',
 'result': 'There were 4 actors who played in Top Gun.'}

Use separate LLMs for Cypher and answer generation​

You can use the cypher_llm and qa_llm parameters to define different llms

chain = GraphCypherQAChain.from_llm(
    graph=graph,
    cypher_llm=ChatOpenAI(temperature=0, model="gpt-3.5-turbo"),
    qa_llm=ChatOpenAI(temperature=0, model="gpt-3.5-turbo-16k"),
    verbose=True,
)
chain.invoke({"query": "Who played in Top Gun?"})


> Entering new GraphCypherQAChain chain...
Generated Cypher:
MATCH (a:Actor)-[:ACTED_IN]->(m:Movie)
WHERE m.name = 'Top Gun'
RETURN a.name
Full Context:
[{'a.name': 'Anthony Edwards'}, {'a.name': 'Meg Ryan'}, {'a.name': 'Val Kilmer'}, {'a.name': 'Tom Cruise'}]

> Finished chain.
{'query': 'Who played in Top Gun?',
 'result': 'Anthony Edwards, Meg Ryan, Val Kilmer, and Tom Cruise played in Top Gun.'}

Ignore specified node and relationship types​

You can use include_types or exclude_types to ignore parts of the graph schema when generating Cypher statements.

chain = GraphCypherQAChain.from_llm(
    graph=graph,
    cypher_llm=ChatOpenAI(temperature=0, model="gpt-3.5-turbo"),
    qa_llm=ChatOpenAI(temperature=0, model="gpt-3.5-turbo-16k"),
    verbose=True,
    exclude_types=["Movie"],
)
# Inspect graph schema
print(chain.graph_schema)
Node properties are the following:
Actor {name: STRING}
Relationship properties are the following:

The relationships are the following:

Validate generated Cypher statements​

You can use the validate_cypher parameter to validate and correct relationship directions in generated Cypher statements

chain = GraphCypherQAChain.from_llm(
    llm=ChatOpenAI(temperature=0, model="gpt-3.5-turbo"),
    graph=graph,
    verbose=True,
    validate_cypher=True,
)
chain.invoke({"query": "Who played in Top Gun?"})


> Entering new GraphCypherQAChain chain...
Generated Cypher:
MATCH (a:Actor)-[:ACTED_IN]->(m:Movie)
WHERE m.name = 'Top Gun'
RETURN a.name
Full Context:
[{'a.name': 'Anthony Edwards'}, {'a.name': 'Meg Ryan'}, {'a.name': 'Val Kilmer'}, {'a.name': 'Tom Cruise'}]

> Finished chain.
{'query': 'Who played in Top Gun?',
 'result': 'Anthony Edwards, Meg Ryan, Val Kilmer, Tom Cruise played in Top Gun.'}

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