참고 자료: https://learn.deeplearning.ai/courses/knowledge-graphs-rag/lesson/1/introduction
What is Knowledge Graph?
A Database that stores information in nodes and relationships
- provides way to sort and organize data
- emphasizes the relationship between things
- uses graph based structure:
- nodes: represents entity
- edges: represents relationship between nodes
Fundamentals
Nodes and Edges
Representation: (Person) - [Knows] - (Person)
Nodes are “in” relationship, relation with properties
Representation: (Person) - [TEACHES] → (Course) ← [INTRODUCES] - (Person)
- Like node, Edges also has key/value structure
Knowledge Graph Overview:
- Knowledge Graph: Stores information in nodes and relationships
- Nodes and Relationships: Both can have properties
- Nodes: Can be labeled to group them together
- Relationships: Always have a type and direction
Querying Knowledge Graphs
- Knowledge Graph used: Neo4jGraph
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from langchain_community.graphs import Neo4jGraph
kg = Neo4jGraph(
url=NEO4J_URI, username=NEO4J_USERNAME, password=NEO4J_PASSWORD, database=NEO4J_DATABASE
)
(Person) - [ACTED_IN] → (Movie)
Node properties
Edges-Relationships between a Person and a Movie
- enables description of perplex situations when a person acted in AND directed a movie
Cypher
- Neo4j’s query language
- uses pattern matching to find thins inside of the grass
Basic
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# number of all the nodes
cypher = """
MATCH (n)
RETURN count(n)
"""
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result = kg.query(cypher)
result
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[{'count(n)': 171}]
Alias
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cypher = """
MATCH (n)
RETURN count(n) AS numberOfNodes
"""
result = kg.query(cypher)
result
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[{'numberOfNodes': 171}]
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print(f"There are {result[0]['numberOfNodes']} nodes in this graph.")
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There are 171 nodes in this graph.
Match
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cypher = """
MATCH (n:Movie)
RETURN count(n) AS numberOfMovies
"""
kg.query(cypher)
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[{'numberOfMovies': 38}]
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cypher = """
MATCH (tom:Person {name:"Tom Hanks"})
RETURN tom
"""
kg.query(cypher)
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[{'tom': {'born': 1956, 'name': 'Tom Hanks'}}]