Cypher is a declarative query language recently added to the Neo4j graph database. In this talk we explain the motivations for creating this language, describe its current features and design, and dive a little into its implementation. Finally, we discuss the future direction of how we expect the language to evolve.

1. FOSDEM 2012
Graph Processing Room
5 Feb 2012
Cypher Query Language
Andrés Taylor and Alistair Jones
Wednesday, February 8, 2012

2. What is Cypher?
• Graph Query Language for Neo4j
• Aims to make querying simple
Wednesday, February 8, 2012

3. Motivation
Something new?
• Existing Neo4j query mechanisms were not
simple enough
• Too verbose (Java API)
• Too prescriptive (Gremlin)
Wednesday, February 8, 2012

4. Motivation
SQL?
• Unable to express paths
• these are crucial for graph-based
reasoning
• neo4j is schema/table free
Wednesday, February 8, 2012

5. Motivation
SPARQL?
• SPARQL designed for a different data model
• namespaces
• properties as nodes
Wednesday, February 8, 2012

6. Design
Wednesday, February 8, 2012

7. Design Decisions
Declarative
Imperative Declarative
follow relationship specify starting point
breadth-first vs depth-first specify desired outcome
explicit algorithm algorithm adaptable
based on query
Wednesday, February 8, 2012

8. Design Decisions
Pattern matching
Wednesday, February 8, 2012

9. Design Decisions
Pattern matching
A
B C
Wednesday, February 8, 2012

10. Design Decisions A
Pattern matching
B C
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11. Design Decisions A
Pattern matching
B C
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12. Design Decisions A
Pattern matching
B C
Wednesday, February 8, 2012

13. Design Decisions A
Pattern matching
B C
Wednesday, February 8, 2012

14. Design Decisions
ASCII-art patterns
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15. Design Decisions
ASCII-art patterns
() --> ()
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16. Design Decisions
ASCII-art patterns
A B
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17. Design Decisions
ASCII-art patterns
A B
(A) --> (B)
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18. Design Decisions
ASCII-art patterns
LOVES
A B
Wednesday, February 8, 2012

19. Design Decisions
ASCII-art patterns
LOVES
A B
A -[:LOVES]-> B
Wednesday, February 8, 2012

20. Design Decisions
ASCII-art patterns
A B C
Wednesday, February 8, 2012

21. Design Decisions
ASCII-art patterns
A B C
A --> B --> C
Wednesday, February 8, 2012

22. Design Decisions
ASCII-art patterns
A
B C
Wednesday, February 8, 2012

23. Design Decisions
ASCII-art patterns
A
B C
A --> B --> C, A --> C
Wednesday, February 8, 2012

24. Design Decisions
ASCII-art patterns
A
B C
A --> B --> C, A --> C
A --> B --> C <-- A
Wednesday, February 8, 2012

25. Design Decisions
Variable length paths
A B
A B
A B
...
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26. Design Decisions
Variable length paths
A B
A B
A B
...
A -[*]-> B
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27. Design Decisions
Optional relationships
A B
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28. Design Decisions
Optional relationships
A B
A -[?]-> B
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29. Design Decisions
Closures
start london = node(1), moscow = node(2)
match path = london -[*]-> moscow
where all(city in nodes(path) where city.capital = true)
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30. Design Decisions
Parsed, not an internal DSL
Execution Semantics Serialisation
Type System Portability
Wednesday, February 8, 2012

31. Design Decisions
Familiar for SQL users
select
start
from
match
where
where
group by
return
order by
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32. Implementation
Wednesday, February 8, 2012

33. Implementation
Execution Plan
start n=node(0)
return n
Parameters()
Nodes(n)
Extract([n])
ColumnFilter([n])
Wednesday, February 8, 2012

34. Implementation
Execution Plan
start n=node(0)
match n-[*]-> b
return n.name, n, count(*)
order by n.age
Parameters()
Nodes(n)
PatternMatch(n-[*]->b)
Extract([n.name, n])
EagerAggregation( keys: [n.name, n], aggregates: [count(*)])
Extract([n.age])
Sort(n.age ASC)
ColumnFilter([n.name,n,count(*)])
Wednesday, February 8, 2012

35. Implementation
Execution Plan
start n=node(0)
match n-[*]-> b
return n.name, n, count(*)
order by n.name
Parameters()
Nodes(n)
PatternMatch(n-[*]->b)
Extract([n.name, n])
Sort(n.name ASC,n ASC)
EagerAggregation( keys: [n.name, n], aggregates: [count(*)])
ColumnFilter([n.name,n,count(*)])
Wednesday, February 8, 2012

36. Thanks for Listening!
Questions?
Andrés Taylor andres.taylor@neotechnology.com @andres_taylor
Alistair Jones alistair.jones@neotechnology.com @apcj
Wednesday, February 8, 2012