The document provides a comprehensive overview of Neo4j, a graph database, focusing on its query language, Cypher. It explains how to work with graph structures, including creating, matching, and deleting nodes and relationships, as well as utilizing pattern matching and aggregation functionalities. Additionally, it highlights use cases and examples of graph data modeling and querying in various applications.

1. (Neo4j)-[: ]->Cypher
Michael Hunger - Neo Technology
1

2. (Michael) -[:WORKS_ON]-> (Neo4j)
console
Cypher community
graph
Community
ME
Server
Spring Cloud
2

3. 3

4. is a
4

5. NOSQL Neo4j
5

6. Graph Database
6

7. 7

8. We're talking about a
Property Graph
7

9. We're talking about a
Property Graph
Nodes
7

10. We're talking about a
Property Graph
Nodes
Relationships
7

11. We're talking about a
Property Graph
Em Joh
il a n
knows knows
Alli Tob Lar
Nodes
son ias knows s
knows
And And knows
knows rea rés
s
knows knows knows
Pet Miic
Mc knows Ian
er knows a
a
knows knows
De Mic
lia h ael
Relationships
Properties (each a key+value)
+ Indexes (for easy look-ups)
7

12. 7

13. 8

14. (Neo4j) -[:IS_A]-> (Graph Database)
Lucene
Sharding 1 M/s
Master/
Index
LS
Slave
TRAVERSA
HIG
TES
H_A
VA RA
G
IL. TE
IN
PROVIDES ACID
Server RUN
S_A LI TX
S CE
NS
ED
_L
ES_T
Ruby IK
RU
JS E
MySQL
S
_A
NS
SC AL
O
Clojure
_O
NS
.net
RU
N Mongo
34bn
embedded Heroku
Nodes 9

15. How do you query this
graph database?
10

16. With a Graph Query
Language:
Cypher
11

17. What is Cypher?
๏Pattern-Matching Query Language
๏Humane language
๏Expressive
๏Declarative: Say what you want, not how
๏borrows from well known query langs
๏Aggregation, Ordering, Limit
๏Update the Graph
12

18. Something new? Why?
๏ Existing Neo4j query mechanisms were not simple enough
• Too verbose (Java API)
• Too prescriptive (Gremlin)
๏ SQL: Unable to express paths
• these are crucial for graph-based reasoning
• Neo4j is schema/table free
๏ SPARQL: designed for a different data model
• namespaces
• properties as nodes
13

19. A Graph
Can‘t see the Patterns for the Trees
http://maxdemarzi.com/2012/02/13/visualizing-a-network-with-cypher/
14

20. It‘s all about Patterns
A
B C
We want to find this Pattern!
15

21. Patterns in a Graph
16

22. 17

23. 18

24. 19

25. 20

26. Patterns as ASCII-ART
21

27. Patterns as ASCII-ART
() --> ()
21

28. Named Nodes
A B
22

29. Named Nodes
A B
(A) --> (B)
22

30. Named Directed Rels
LOVES
A B
23

31. Named Directed Rels
LOVES
A B
A -[:LOVES]-> B
23

32. Paths
A B C
24

33. Paths
A B C
A --> B --> C
24

34. Cyclic-Path-Patterns
A
B C
25

35. Cyclic-Path-Patterns
A
B C
A --> B --> C, A --> C
25

36. Cyclic-Path-Patterns
A
B C
A --> B --> C, A --> C
A --> B --> C <-- A
25

37. Variable Length Paths
A B
A B
A B
...
A -[*]-> B 26

38. Optional Relationships
A B
27

39. Optional Relationships
A B
A -[?]-> B
27

40. 28

41. How does it work?
28

42. How does it work?
28

43. How does it work?
// lookup starting point in an index
start n=node:People(name = ‘Andreas’)
And
rea
s
28

44. How does it work?
// lookup starting point in an index
then traverse to find results
start n=node:People(name = ‘Andreas’)
match (n)--()--(foaf) return foaf
And
rea
s
28

45. 28

46. The Parts of Cypher
29

47. 30

48. Cypher: START + RETURN
๏ START <lookup> RETURN <expressions>
๏ START binds terms using simple look-up
•directly using known ids
•or based on indexed Property
๏ RETURN expressions specify result set
30

49. Cypher: START + RETURN
๏ START <lookup> RETURN <expressions>
๏ START binds terms using simple look-up
•directly using known ids
•or based on indexed Property
๏ RETURN expressions specify result set
// lookup node id 0, return that node
start n=node(0) return n
// lookup node in Index, return that node
start n=node:Person(name="Andreas") return n
// lookup all nodes, return all name properties
start n=node(*) return n.name
30

50. 31

51. Cypher: MATCH
๏ START <lookup> MATCH <pattern> RETURN <expr>
๏ MATCH describes a pattern of nodes+relationships
•node terms in optional parenthesis
•lines with arrows for relationships
31

52. Cypher: MATCH
๏ START <lookup> MATCH <pattern> RETURN <expr>
๏ MATCH describes a pattern of nodes+relationships
•node terms in optional parenthesis
•lines with arrows for relationships
// lookup 'n', traverse any relationship to some 'm'
start n=node(0) match (n)--(m) return n,m
// any outgoing relationship from 'n' to 'm'
start n=node(0) match n-->m return n,m
// only 'KNOWS' relationships from 'n' to 'm'
start n=node(0) match n-[:KNOWS]->m return n,m
// from 'n' to 'm' and capture the relationship as 'r'
start n=node(0) match n-[r]->m return n,r,m
// from 'n' outgoing to 'm', then incoming from 'o'
start n=node(0) match n-->m<--o return n,m,o
31

53. 32

54. Cypher: RETURN
๏ RETURN <expressions>, aggregation(expr) as alias
๏ RETURN nodes, rels, properties
๏ RETURN expressions of functions and operators
๏ RETURN aggregation functions on the above
32

55. Cypher: RETURN
๏ RETURN <expressions>, aggregation(expr) as alias
๏ RETURN nodes, rels, properties
๏ RETURN expressions of functions and operators
๏ RETURN aggregation functions on the above
// aggregate on n, count the m‘s
start n=node(0) match n--m return n,count(*)
// alias n.name as name
start n=node(0) return n.name as name
// aggregate m‘s into list
start n=node(*) match n--m return n,collect(m)
// filter m‘s by name
start n=node(*) match n--m return n,filter(x in collect(m):
m.name ˜= /A.*/) as a_block
32

56. 33

57. Cypher: WHERE
๏ START <lookup> [MATCH <pattern>]
WHERE <condition> RETURN <expr>
๏ WHERE filters nodes or relationships
•uses expressions to constrain elements
33

58. Cypher: WHERE
๏ START <lookup> [MATCH <pattern>]
WHERE <condition> RETURN <expr>
๏ WHERE filters nodes or relationships
•uses expressions to constrain elements
// lookup all nodes as 'n', constrained to name 'Andreas'
start n=node(*) where n.name='Andreas' return n
// filter nodes where age is less than 30
start n=node(*) where n.age<30 return n
// filter using a regular expression
start n=node(*) where n.name =~ /Tob.*/ return n
// filter for a property exists
start n=node(*) where has(n.name) return n
33

59. 34

60. Cypher: CREATE
๏ CREATE <node>[,node or relationship] RETURN <expr>
•create nodes with optional properties
•create relationship (must have a type)
34

61. Cypher: CREATE
๏ CREATE <node>[,node or relationship] RETURN <expr>
•create nodes with optional properties
•create relationship (must have a type)
// create an anonymous node
create n
// create node with a property, returning it
create n={name:'Andreas'} return n
// lookup 2 nodes, then create a relationship and return it
start n=node(0),m=node(1) create n-[r:KNOWS]-m return r
// lookup nodes, then create a relationship with properties
start n=node(1),m=node(2) create n-[r:KNOWS {since:2008}]->m
34

62. 35

63. Cypher: CREATE UNIQUE
๏ CREATE UNIQUE node-[rel]->(node {prop : value})
•„fixes“ the graph
•starts at bound nodes, properties rels and nodes by
comparing types and
tries to find
•if not found creates them
35

64. Cypher: CREATE UNIQUE
๏ CREATE UNIQUE node-[rel]->(node {prop : value})
•„fixes“ the graph
•starts at bound nodes, properties rels and nodes by
comparing types and
tries to find
•if not found creates them
// create a new relationship
start n=.., m=.. create unique n-[:KNOWS]->m
// create a new node AND relationship
start n=... create unique n-[:TAGGED]->(tag {name:“neo“})
// matches the tag node by name only creates new relationship
start n=... create unique n-[:TAGGED]->(tag {name:“neo“})
35

65. 36

66. Cypher: SET
๏ SET [<node property>] [<relationship property>]
•update a property on a node or relationship
•must follow a START
36

67. Cypher: SET
๏ SET [<node property>] [<relationship property>]
•update a property on a node or relationship
•must follow a START
// update the name property
start n=node(0) set n.name='Peter'
// update many nodes, using a calculation
start n=node(*) set n.size=n.size+1
// match & capture a relationship, update a property
start n=node(1) match n-[r]-m set r.times=10
36

68. 37

69. Cypher: DELETE
๏ DELETE [<node>|<relationship>|<property>]
•delete a node, relationship or property
•toall relationships must be deleted first
delete a node,
37

70. Cypher: DELETE
๏ DELETE [<node>|<relationship>|<property>]
•delete a node, relationship or property
•toall relationships must be deleted first
delete a node,
// delete a node
start n=node(5) delete n
// remove a node and all relationships
start n=node(3) match n-[r]-() delete n, r
// remove a property
start n=node(3) delete n.age
37

71. More Advanced
Examples
38

72. START user = node(1)
MATCH user -[user_skill]-> skill
RETURN skill, user_skill
SELECT skills.*, user_skill.*
FROM users
JOIN user_skill ON users.id = user_skill.user_id
JOIN skills ON user_skill.skill_id = skill.id WHERE users.id = 1
39

73. Example:
Old, Influential Friends
START me = node(...)
MATCH (me) - [f:FRIEND] - (old_friend)
- [:FRIEND ] - (fof)
WHERE ({today}-f.begin) > 365*10
WITH old_friend, collect(fof.name) as names
WHERE length(names) > 100
RETURN old_friend, names
ORDER BY old_friend.name ASC
f:FRIEND :FRIEND
me friend fof

74. Example:
Simple Recommendation
START me = node(...)
MATCH (me) -[r1:RATED ]->(thing)
<-[r2:RATED ]- (someone)
-[r3:RATED ]->(cool_thing)
WHERE ABS(r1.stars-r2.stars) <= 2
AND r3.stars > 3
RETURN cool_thing, count(*) AS cnt
ORDER BY cnt DESC LIMIT 10
r1:RATED thing r2:RATED
me so
TED
r 3: RA
cool
thing 41

75. Cypher Cheat Sheet
http://neo4j.org/resources/cypher
42

76. The Rabbithole
http://console.neo4j.org
This Graph: http://tinyurl.com/7cnvmlq
43

77. How to use Cypher
in YOUR programs
44

78. Neo4j API
ExecutionEngine engine = new ExecutionEngine(graphDB);
String query = „start n=node:Person(name={name})
match n-[:ACTS_IN]->movie<-[:ACTS_IN]-friend
return friend“;
ExecutionResult result = engine.query(query, map(„name“, „Keanu“);
for (Map<String,Object> row : result) {
Node friend = row.get(„friend“);
}
Iterator<Node> friends = result.columnAs(„friend“);
http://bit.ly/cypher-queries
45

79. How to get started?
46

80. How to get started?
๏ Documentation
46

81. How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference
46

82. How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference
• http://console.neo4j.org
46

83. How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference
• http://console.neo4j.org
• Neo4j in Action
46

84. How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference
• http://console.neo4j.org
• Neo4j in Action
• Good Relationships
46

85. How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference
• http://console.neo4j.org
• Neo4j in Action
• Good Relationships
๏ Get Neo4j
46

86. How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference
• http://console.neo4j.org
• Neo4j in Action
• Good Relationships
๏ Get Neo4j
• http://neo4j.org/download
46

87. How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference
• http://console.neo4j.org
• Neo4j in Action
• Good Relationships
๏ Get Neo4j
• http://neo4j.org/download
• http://addons.heroku.com/neo4j/
๏ Participate
• http://groups.google.com/group/neo4j
• http://neo4j.meetup.com
46

88. How to get started?
๏ Documentation
• docs.neo4j.org - tutorials+reference
• http://console.neo4j.org
• Neo4j in Action
• Good Relationships
๏ Get Neo4j
• http://neo4j.org/download
• http://addons.heroku.com/neo4j/
๏ Participate
• http://groups.google.com/group/neo4j
• http://neo4j.meetup.com
• a session like this one ;)
46

89. http://console.neo4j.org/r/GoT
https://dl.dropbox.com/u/14493611/got.txt
47

90. Neo4j-JDBC Driver & MovieDB Dataset
http://blog.neo4j.org/2012/06/wanted-your-
help-in-testing-neo4j-jdbc.html
48

91. Got a Conference? Need a Dataset?
http://blog.neo4j.org/2012/08/at-conference-
need-dataset-neo4j-at.html
49

92. Neo4j in Action
Software Metrics
50

93. Graphs in Software Technolgoy
๏ UML Diagrams are graphs
๏ dependencies between classes, packages, modules etc are graphs
๏ Software Metrics use dependency analysis
๏ Visualizations
๏ Cyclomatic Complexity,
๏ Fan-in (afferent-coupling) / Fan-out (efferent coupling) etc.
51

94. Code City
52

95. Class Diagram is a Graph
53

96. SonarJ
54

97. But there is more
๏Visualize & query Method, Field
dependencies
๏Collaborative filtering (co-usage)
๏Ranking
๏God classes
๏Paths between classes
55

98. Welcome to Class-Graph
๏take a JAR
๏put it under ASM
๏scan it superfast
๏pull everything into Neo4j
๏add categories, indexes
๏Have Fun
http://github.com/jexp/class-graph 56

99. Welcome to Class-Graph
57

100. Interactive Hands-On Session
๏Lots of tasks
๏use Cypher to solve them
http://neo4j.org/resources/cypher
๏be creative, work together
๏ask !
๏Server http://bit.ly/innoq-neo4j
๏just the beginning
58

101. Task: Find java.lang.Number and return it
59

102. Task: Find java.lang.Number and return it
START o=node:types(name="java.lang.Number")
RETURN o;
59

103. Task: Subclasses of Number?
•Return just the name
•Order them alphabetically
60

104. Task: Subclasses of Number?
START n=node:types(name="java.lang.Number")
MATCH n<-[:SUPER_TYPE]-s
RETURN s.name
ORDER BY s.name;
•Return just the name
•Order them alphabetically
60

105. Task: Which Methods does it have / how many
•Find the top 5 classes with the most members
61

106. Task: Which Methods does it have / how many
START n=node:types(name="java.lang.Number")
MATCH n-[:METHOD_OF|FIELD_OF]->m
RETURN m;
•Find the top 5 classes with the most members
61

107. Task: Calculate the fan-out of
java.lang.StringBuilder
•Calculate fan-in
•Which class has the highest fan-out
•What about package-level? 62

108. Task: Calculate the fan-out of
java.lang.StringBuilder
START o=node:types(name="j.l.StringBuilder")
MATCH o-[:FIELD_OF]->f-[:FIELD_TYPE]->tf,
o-[:METHOD_OF]->m-[:PARAM_TYPE]->tp,
m-[:RETURN_TYPE]->tr
RETURN o,count(distinct tf)
+ count(distinct tp)
+ count(distinct tr) as fan_out;
•Calculate fan-in
•Which class has the highest fan-out
•What about package-level? 62

109. Task: Find longest Inheritance Path
63

110. Task: Find longest Inheritance Path
start c=node:types(name="java.lang.Object")
match path=p<-[:SUPER_TYPE*]-c
return extract(n in nodes(path) : n.name),
length(path) as len
order by len desc
limit 5;
63

111. Task: Find the class that used IOException
most often
64

112. Task: Find the class that used IOException
most often
START ex=node:types(name="java.io.IOException"
MATCH ex<-[:THROWS]-m<-[:METHOD_OF]-c
RETURN c, count(*)
ORDER BY count(*)
LIMIT 5;
64

113. Task: Which other classes did classes that
threw IOException use most often?
•What could be a source of IOExceptions
65

114. Task: Which other classes did classes that
threw IOException use most often?
START ex=node:types(name="java.io.IOException")
MATCH ex<-[:THROWS]-m<-[:METHOD_OF]-c,
mbr<-[:METHOD_OF|FIELD_OF]-c,
mbr-[:FIELD_TYPE|PARAM_TYPE|
RETURN_TYPE|THROWS]->other_type
WHERE other_type.name =~ /.+[.].+/
RETURN other_type.name, count(*)
ORDER BY count(*) desc
LIMIT 10;
•What could be a source of IOExceptions
65

115. Task: Find a class you like and add a field with
your name and some type
66

116. Task: Find a class you like and add a field with
your name and some type
START c=node:types(name="void"),
t=node:types(name="java.lang.reflect.Proxy")
CREATE c-[:FIELD_OF]->(field {name:“Michael“})
-[:FIELD_TYPE]->t;
66

117. Task: Delete the most annoying class and all its
methods, fields and their relationships
67

118. Task: Delete the most annoying class and all its
methods, fields and their relationships
START c=node:types(name="java.awt.List"),
MATCH c-[r1:FIELD_OF|METHOD_OF]->mbr-[r2]-()
c-[r]-()
DELETE c,mbr,r1,r2,r;
67