openCypher: Naming and Addressing Multiple Graphs

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Multiple Graph Processing
Naming and Addressing
Alastair Green
Neo Technology Cypher Language Group

opencypher.org | opencypher@googlegroups.com
Problem #1 Loading and saving
> 1 Store → > 1 persistent graph
Local File
System
BOLT

Problem #1 Loading and saving
Neo4j instance
= 1 graph
Local File
System
BOLT GraphX/Frame
conventional
V+E files = 1
graph
Neo4j CSV
fileset = 1 graph
.graphml = 1
graph
.nq = n graphs

Containers and storage (rep + encoding) standards
Storage type Container type URI scheme Storage Format PG?
Neo4j Neo4j Server bolt:// Opaque Y
CSV fileset LFS, HDFS ... file://, hdfs:// Under-specified Y
.graphml LFS, HDFS ... file://, hdfs:// Well-specified N
GraphX/Frames
V+E files
HDFS, LFS, ... file://, hdfs:// Under-specified N
N-Quads LFS, HDFS, ... file://, hdfs:// Well-specified N
...

URI [+ directory/file convention] [+ PG convention]
How do we know where to find edges and vertices?
file:///path/to/the/data/devices/edges/*.csv | .txt
file:///path/to/the/data/devices/vertices/*.csv
How do we know where to find labels/types in *.csv?
What happens if we want to model graph properties?
■ These questions have to be answered by (small) specifications
■ Conventional/assumed answers may not be systematic or complete

graph:// URIs
A URI scheme that can
■ incorporate other URI schemes
■ register/refer to sub-specifications or URI scheme extensions that define
PG conventions
■ allow the hierarchical path convention used by many URI schemes to be
used to locate/identify containers or “spaces”
■ allows every path to terminate with the unqualfied name of a graph
graph://bolt/’bolt+routing://neo4j-server:4567/social-networks/europe’
The meaning/depth of the path is implementation determined
It might imply folders, partitions or instances or tenants … or nothing

Loading and saving graphs in Cypher queries*
IN GRAPH
EuropeSocialNetwork
AT
MATCH
(p1)-[:friends]-(p2)-[:friends]-(p3)-[:friends]-(p1)
CREATE
(t:FriendsTriangle),
(t)-[:contains]->(p1),
(t)-[:contains]->(p2),
(t)-[:contains]->(p3)
IN GRAPH
FriendsTriangles
AT
graph://graphml+pg/’hdfs://my-big-data/europe/snapshots/2017-08-23/friendsTriangles’
* Example use case and pattern concepts from LDBC QL TF input by Hannes Voigt
Load
Save

Or perhaps … or as well
GRAPH [europe]
AT
IN GRAPH
europe
MATCH
DEFAULT GRAPH AT
MATCH
Implicit?
Anonymous
Explicit

Problem #2 Graphs in the scope of queries
Cypher queries are made up of parts
■ Intermediate results are chained from part to part
■ We will want to allow those results to be graphs
■ There could be more than one, so names are needed
■ And it might be good to allow intermediate graphs to be persisted
WITH or IN?
A named graph could have global scope in the query (cf. current Cypher anon graph)
This would mean it could always be referred to in a later part
And also used in RETURN as a final result

Problem #3 Graphs in the scope of sub-queries
A sub-query must be able to return a graph
IN
{IN GRAPH someGraph MATCH CREATE ... AS GRAPH} // anonymous
MATCH
...
and it might be useful to name it (and perhaps persist it) for later reference
DECLARE DEFAULT GRAPH AT
IN
{MATCH ... CREATE ... AS GRAPH g [AT <url>]} // named [optionally saved]
MATCH
...

Problem #4 Queries returning graphs
Persisting a graph is not the same as returning a graph to a caller
■ Critical to allowing graph queries to be part of function chains
■ May be more than one graph that results from a query
■ If so then each graph needs a name
CREATE
(t:FriendsTriangle), (t)-[:contains]->(p1),
(t)-[:contains]->(p2),(t)-[:contains]->(p3)
IN GRAPH
FriendsTriangles
RETURN
FriendsTriangles

Problem #5 Views
Logically we compose queries as functions over views q(v(G))
IN GRAPH
EuropeSocialNetwork
MATCH
CREATE
(t:FriendsTriangle), (t)-[:contains]->(p1),
(t)-[:contains]->(p2), (t)-[:contains]->(p3)
IN GRAPH
FriendsTriangles AS VIEW
IN GRAPH
FriendsTriangles
MATCH
...

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