Neo4j comes with enhanced connectivity of data and whiteboard friendly paradigm. It also brings a gremlin in your code : one of the supported graph query language brings a refreshing look at how one can search for data in a vast and interconnect web of data. Gremlin provides an abstract layer that make it easy to express your business logic without fighting with the code. It may even change your mind on object oriented programming.

1. A gremlin
in your graph
in your graph
Montreal, Québec, Canada, February, 28th 2014

2. What is gremlin?
G : graph, or the dataset
V : Vertices, or nodes or objects
E : Edges, or links or relations

4. graph database, http://www.neo4j.org/

5. Speaker
Damien Seguy
dams@php.net
Exakat : Expert services in PHP

6. Yes we take
questions
?

7. Graph Database
http://www.neo4j.org/
http://localhost:7474/
Console -> Gremlin
==>
==>
,,,/
==>
(o o)
==> -----oOOo-(_)-oOOo----==>
==> Available variables:
==>
g = (neo4jgraph[EmbeddedGraphDatabase [data/graph.db]]
==> , null) out = (java.io.PrintStream@398a3257
==> , null)
gremlin>
Console in web browser!

8. Welcome to the
graph
g is the graph where the nodes live
v represents all the vertices
g.v(1) =>
Nodes always have an id
v(1)

9. Properties
Graph is schemaless
g.v(1).id
=> 1
g.v(1).name
=> ext/datetime
g.v(1).version => null

10. Node discovery
g.v(2).map =>
{name=timezonedb, version=2013.9}
map is convenient to discover the
graph

11. In the graph
Only objects and relations
Vertices have id and properties
Edges have id, label and properties

12. Edges
g.v(1).in => v(4)
g.v(1).out => v(2)
v(3)
g.v(1).both => v(2)
v(3)
v(4)
Directed graph

13. g.v(1).inE.id => 2
3
4
8
g.v(1).inE.label => WROTE
WROTE
WROTE
HAS

14. PECL database
database of PHP extension authors.
The extensions are stored in categories
http://pecl.php.net/
Gephi

15. Following edges
g.v(1).in(‘WROTE’).name => Derick Rethans
Hannes Magnusson
Jeremy Mikola
g.v(1).in(‘WROTE’,‘HAS’).name =>
/*same as previous plus */ DB

16. Collaborators
g.v(2).out(‘WROTE’).in(‘WROTE’).name =>
Hannes Magnusson
Jeremy Mikola
Derick Rethans

17. Collaborators
g.v(2).out(‘WROTE’).in(‘WROTE’).
except(g.v(2)).name =>
Hannes Magnusson
Jeremy Mikola

18. Intro recap
nodes and vertices : basic blocs
in and out (and both) : navigation
except(), in(‘label’) : filtering

19. Traversing the
graph
Means reading information in the graph
Traversing involves listing nodes then following
links until all conditions are met
The graph contains Vertices and Edges. Is there
anything else ?

20. PECL database
Authors
Ext
Categories

21. Count authors
count()
All vertices are
created equal

22. Count contributors
g.V.out(‘wrote’)
.count()
=> 5
Too manys!

23. Arrays or pipes
g.V.out(‘wrote’)[1]
v(12)
g.V.out(‘wrote’)[1..2]
.name ext/xdebug
ext/mongo

24. Count contributors
g.V.in(‘wrote’)
.unique()
.count()==> 3

25. Gremlin functions
Pipe level function
in, out, unique, count,
Node level function
map, has, filter{}
Value level
{property}

26. Property level
// making name UPPERCASE
g.v(79).name.toUpperCase(); EXT/GEARMAN
// size of the name’s string
g.v(130).name.toList().size(); 13
// extracting words http://groovy.codehaus.o
in a string
Documentation
g.v(146).transform{ it.name.tokenize();}
[Johann-Peter, Hartmann]

27. Vertex level
g.v(130).map;
{name=Ben Ramsey}
g.v(14).propertykeys name
g.v(12).setProperty(‘ext_nb’,
g(12).out(‘wrote’).count()
);

28. Collaborating
Adding collaborators to the graph
g.addEdge(
g.v(1),
g.v(1).out(‘WROTE’).
in(‘WROTE’).
except(g.v(1)),
‘COLLABORATE’);
==> No signature of method: com.tinkerpop.gremlin.groovy.GremlinGro
ovyPipeline.except() is applicable for argument types: (com.tinkerp
op.blueprints.pgm.impls.neo4j.Neo4jVertex) values: [v[1]]
==> Possible solutions: except(java.util.Collection), select(),
next(), reset(), cap(), toSet()
Except() produces a pipe!
g.addedge doesn’t accept it

29. Collaborating
Adding collaborator
g.addEdge(
g.v(1),
g.v(1).out(‘WROTE’).
in(‘WROTE’).
except(g.v(1)).next(),
‘COLLABORATE’);
Adding collaborators
g.v(1).out(‘WROTE’).in(‘WROTE’).except(g.v(1)).each{
g.addEdge(g.v(1), it, ‘COLLABORATE’)
}
wonderful world of closures

30. Working with pipes
Pipes functions often offer possibility for closure
Closure is between {}
and uses ‘it’ as current node
Closure often have a standard default behavior, so
they are sometimes stealth

31. Filtering
filter links by label (in/out/both(‘label’))
Filter node with has(‘property’,
‘value’)
or
hasNot(‘property’, null)
Filter authors with 14 or more extensions
g.V.in(‘WROTE’).filter{it.out(‘WROTE’).count() > 14}
Ilia Alshanetsky, Wez Furlong, Sara Golemon
Filter allows us to work within the pipe

32. Filtering
List of contributors with more ext in two categories
g.V.in(‘wrote’).filter{
it.out(‘wrote’).in(‘has’).unique().count() > 2
}.name
Filter longer than query ?

33. GroupCount
groupCount(m)
Number of categories by author
g.V.out(‘wrote’).in(‘has’).groupCount(m)
Apparently counted but
who is v(274) ?
==> v[380]=1=
v[379]=1==>
v[378]=2==>
v[273]=2==>
v[274]=2==>
v[272]=2==>
v[173]=3==>
v[240]=2==>

34. GroupCount
g.V.out(‘has’)
.in(‘wrote’)
.groupCount(m)
Georg Richter =2==> Warren Read =2==> Jay Kint =2==> shekhar
euvel =1==>{it.name}
Grant Croker =1

35. GroupCount
Count of categories, without PHP standard
distribution
The second closure counts elements (default +1)
g.V.has(‘wrote’)
.in(‘has’)
.groupCount(m)
{it.name}
{if (!it.name in [‘mysql’, ‘timezonedb’,’gd’,
‘dbase’ /* ....*/]) { it.b + 1;} }

36. Pipes
array notation
closure usage
useful function for pipes :
groupcount, groupby{key}{value}{mapreduce},
ordermap, [n..m] operator,
More on http://gremlindocs.com/

37. Graph modifications
Gremlin allows graph modification
Adding a type property to authors
g.V.in(‘WROTE’).each{
it.setProperty(‘type’, ‘author’);
}

38. Updating on the way
sideEffect runs a closure, but keep running the
query
Adding type to extensions AND categories in the
same query
g.V.as(‘ext’)
.in(‘HAS’)
.sideEffect{
it.setProperty(‘type’, ‘Category’);
.back(‘ext’)
.sideEffect{
it.setProperty(‘type’, ‘Extension’);
}
}

39. back tracking
back( ‘name’ ) : goes back to the vertex or edge
that was named with as(‘name’)
back( n ) : goes back n vertex or edges behind
Make is possible to check a branch, come back and
check another branch

40. Manipulating vertex
g.addVertex(id or null, [property:value,...]);
g.addEdge(origin vertex,
destination vertex,
label,
[property:value...]);
g.removeVertex(vertex);
g.removeEdge(edge);

41. Application to OOP?
Gremlin goes beyond class specifics
g.v(1).out(‘WROTE’).in(‘HAS’).unique().count()
$total = array();
$author = new Author(1);foreach($author>getExtensions() as $ext) {
$total[$ext->getCategory()] = true;}
return count($total);
return count($total);
Gremlin generalizes the navigation

42. Thanks
Dams@php.net
http://www.slideshare.net/dseguy/
on the http://confoo.ca/

43. Kevin Bacon
Suggest collaborators to authors ?
Authors who worked with collaborators but not with
the author, are recommendations
g.V.has(‘name’, ‘contrib’).sideEffect{init =
it}out(‘wrote’).in(‘wrote’).except(init).has(‘name’,‘con
trib2’).path