What is Cypher Query Language?

Cypher is a graph query language developed initially for the Neo4j graph database but has now been open-sourced through the openCypher project. It is inspired by SQL and allows us to focus on what to get rather than how to get it.

Why Cypher?

Cypher is like SQL for graphs. It is the go-to query language for the property graph model because of the features discussed below:

Syntax

Cypher has English-like syntax, which makes it human-readable.

Easy to learn

Cypher is very similar to other languages and hence easy to learn.

CRUD

Cypher is made for performing CRUDCreate, Read, Update, and Delete operations on graphs.

ASCII-Art

The property graph model comprises nodes and relationships which together make patterns. Cypher is also based on patterns that employ ASCII-Arttext art based on ASCII, hence providing a visual way for querying graphs:

  • Nodes are represented using round brackets () .

  • Relationships are represented using --> or <--.

  • Relationship types are represented using square brackets [].

Cypher also allows specifying labels and properties conveniently.

Example query

Suppose we want a Cypher expression that would represent the following example phrase:

"Joe loves Educative Answers."

Below is the property graph version of the above expression:

Graph representing example phrase

And the Cypher expression is as follows:

Cypher expression for the example phrase

The CREATE clause

We can create the above nodes and relationships using the CREATE clause in Cypher:

CREATE (p:Person {name:"Joe"})-[:LOVES]->(e:Educative {product:"Answers"});
Cypher CREATE clause

The MATCH clause

The MATCH works like SELECT in SQL. We can find out what Educative product Joe loves by using the following MATCH clause:

MATCH (p:Person {name:"Joe"})-[:LOVES]->(e:Educative)
RETURN e.product;
Cypher MATCH clause

Run the terminal below and wait for the Cypher Shell to start. Enter the above CREATE and MATCH queries to see the output. You can also try your own queries:

#*****************************************************************
# Neo4j configuration
#
# For more details and a complete list of settings, please see
# https://neo4j.com/docs/operations-manual/current/reference/configuration-settings/
#*****************************************************************

# The name of the default database
#dbms.default_database=neo4j

# Paths of directories in the installation.
#dbms.directories.data=data
#dbms.directories.plugins=plugins
#dbms.directories.logs=logs
#dbms.directories.lib=lib
#dbms.directories.run=run
#dbms.directories.licenses=licenses
#dbms.directories.transaction.logs.root=data/transactions

# This setting constrains all `LOAD CSV` import files to be under the `import` directory. Remove or comment it out to
# allow files to be loaded from anywhere in the filesystem; this introduces possible security problems. See the
# `LOAD CSV` section of the manual for details.
dbms.directories.import=import

# Whether requests to Neo4j are authenticated.
# To disable authentication, uncomment this line
dbms.security.auth_enabled=false

# Enable this to be able to upgrade a store from an older version.
#dbms.allow_upgrade=true

#********************************************************************
# Memory Settings
#********************************************************************
#
# Memory settings are specified kilobytes with the 'k' suffix, megabytes with
# 'm' and gigabytes with 'g'.
# If Neo4j is running on a dedicated server, then it is generally recommended
# to leave about 2-4 gigabytes for the operating system, give the JVM enough
# heap to hold all your transaction state and query context, and then leave the
# rest for the page cache.

# Java Heap Size: by default the Java heap size is dynamically calculated based
# on available system resources. Uncomment these lines to set specific initial
# and maximum heap size.
#dbms.memory.heap.initial_size=512m
#dbms.memory.heap.max_size=512m

# The amount of memory to use for mapping the store files.
# The default page cache memory assumes the machine is dedicated to running
# Neo4j, and is heuristically set to 50% of RAM minus the Java heap size.
#dbms.memory.pagecache.size=10g

# Limit the amount of memory that all of the running transaction can consume.
# By default there is no limit.
#dbms.memory.transaction.global_max_size=256m

# Limit the amount of memory that a single transaction can consume.
# By default there is no limit.
#dbms.memory.transaction.max_size=16m

# Transaction state location. It is recommended to use ON_HEAP.
dbms.tx_state.memory_allocation=ON_HEAP

#*****************************************************************
# Network connector configuration
#*****************************************************************

# With default configuration Neo4j only accepts local connections.
# To accept non-local connections, uncomment this line:
dbms.default_listen_address=0.0.0.0

# You can also choose a specific network interface, and configure a non-default
# port for each connector, by setting their individual listen_address.

# The address at which this server can be reached by its clients. This may be the server's IP address or DNS name, or
# it may be the address of a reverse proxy which sits in front of the server. This setting may be overridden for
# individual connectors below.
dbms.default_advertised_address=0.0.0.0

# You can also choose a specific advertised hostname or IP address, and
# configure an advertised port for each connector, by setting their
# individual advertised_address.

# By default, encryption is turned off.
# To turn on encryption, an ssl policy for the connector needs to be configured
# Read more in SSL policy section in this file for how to define a SSL policy.

# Bolt connector
dbms.connector.bolt.enabled=true
#dbms.connector.bolt.tls_level=DISABLED
dbms.connector.bolt.listen_address=:7687
dbms.connector.bolt.advertised_address=:7687

# HTTP Connector. There can be zero or one HTTP connectors.
dbms.connector.http.enabled=true
dbms.connector.http.listen_address=:7473
dbms.connector.http.advertised_address=:7473

# HTTPS Connector. There can be zero or one HTTPS connectors.
dbms.connector.https.enabled=false
dbms.connector.https.listen_address=:7473
dbms.connector.https.advertised_address=:7473

# Number of Neo4j worker threads.
#dbms.threads.worker_count=

#*****************************************************************
# SSL policy configuration
#*****************************************************************

# Each policy is configured under a separate namespace, e.g.
#    dbms.ssl.policy.<scope>.*
#    <scope> can be any of 'bolt', 'https', 'cluster' or 'backup'
#
# The scope is the name of the component where the policy will be used
# Each component where the use of an ssl policy is desired needs to declare at least one setting of the policy.
# Allowable values are 'bolt', 'https', 'cluster' or 'backup'.

# E.g if bolt and https connectors should use the same policy, the following could be declared
#   dbms.ssl.policy.bolt.base_directory=certificates/default
#   dbms.ssl.policy.https.base_directory=certificates/default
# However, it's strongly encouraged to not use the same key pair for multiple scopes.
#
# N.B: Note that a connector must be configured to support/require
#      SSL/TLS for the policy to actually be utilized.
#
# see: dbms.connector.*.tls_level

# SSL settings (dbms.ssl.policy.<scope>.*)
#  .base_directory       Base directory for SSL policies paths. All relative paths within the
#                        SSL configuration will be resolved from the base dir.
#
#  .private_key          A path to the key file relative to the '.base_directory'.
#
#  .private_key_password The password for the private key.
#
#  .public_certificate   A path to the public certificate file relative to the '.base_directory'.
#
#  .trusted_dir          A path to a directory containing trusted certificates.
#
#  .revoked_dir          Path to the directory with Certificate Revocation Lists (CRLs).
#
#  .verify_hostname      If true, the server will verify the hostname that the client uses to connect with. In order
#                        for this to work, the server public certificate must have a valid CN and/or matching
#                        Subject Alternative Names.
#
#  .client_auth          How the client should be authorized. Possible values are: 'none', 'optional', 'require'.
#
#  .tls_versions         A comma-separated list of allowed TLS versions. By default only TLSv1.2 is allowed.
#
#  .trust_all            Setting this to 'true' will ignore the trust truststore, trusting all clients and servers.
#                        Use of this mode is discouraged. It would offer encryption but no security.
#
#  .ciphers              A comma-separated list of allowed ciphers. The default ciphers are the defaults of
#                        the JVM platform.

# Bolt SSL configuration
#dbms.ssl.policy.bolt.enabled=true
#dbms.ssl.policy.bolt.base_directory=certificates/bolt
#dbms.ssl.policy.bolt.private_key=private.key
#dbms.ssl.policy.bolt.public_certificate=public.crt
#dbms.ssl.policy.bolt.client_auth=NONE

# Https SSL configuration
# dbms.ssl.policy.https.enabled=true
# dbms.ssl.policy.https.base_directory=certificates/https
# dbms.ssl.policy.https.private_key=private.key
# dbms.ssl.policy.https.public_certificate=public.crt
# dbms.ssl.policy.https.client_auth=NONE

# Cluster SSL configuration
#dbms.ssl.policy.cluster.enabled=true
#dbms.ssl.policy.cluster.base_directory=certificates/cluster
#dbms.ssl.policy.cluster.private_key=private.key
#dbms.ssl.policy.cluster.public_certificate=public.crt

# Backup SSL configuration
#dbms.ssl.policy.backup.enabled=true
#dbms.ssl.policy.backup.base_directory=certificates/backup
#dbms.ssl.policy.backup.private_key=private.key
#dbms.ssl.policy.backup.public_certificate=public.crt

#*****************************************************************
# Logging configuration
#*****************************************************************

# To enable HTTP logging, uncomment this line
#dbms.logs.http.enabled=true

# Number of HTTP logs to keep.
#dbms.logs.http.rotation.keep_number=5

# Size of each HTTP log that is kept.
#dbms.logs.http.rotation.size=20m

# To enable GC Logging, uncomment this line
#dbms.logs.gc.enabled=true

# GC Logging Options
# see https://docs.oracle.com/en/java/javase/11/tools/java.html#GUID-BE93ABDC-999C-4CB5-A88B-1994AAAC74D5
#dbms.logs.gc.options=-Xlog:gc*,safepoint,age*=trace

# Number of GC logs to keep.
#dbms.logs.gc.rotation.keep_number=5

# Size of each GC log that is kept.
#dbms.logs.gc.rotation.size=20m

# Log level for the debug log. One of DEBUG, INFO, WARN and ERROR. Be aware that logging at DEBUG level can be very verbose.
#dbms.logs.debug.level=INFO

# Size threshold for rotation of the debug log. If set to zero then no rotation will occur. Accepts a binary suffix "k",
# "m" or "g".
#dbms.logs.debug.rotation.size=20m

# Maximum number of history files for the internal log.
#dbms.logs.debug.rotation.keep_number=7

#*****************************************************************
# Miscellaneous configuration
#*****************************************************************

# Enable this to specify a parser other than the default one.
#cypher.default_language_version=3.5

# Determines if Cypher will allow using file URLs when loading data using
# `LOAD CSV`. Setting this value to `false` will cause Neo4j to fail `LOAD CSV`
# clauses that load data from the file system.
#dbms.security.allow_csv_import_from_file_urls=true


# Value of the Access-Control-Allow-Origin header sent over any HTTP or HTTPS
# connector. This defaults to '*', which allows broadest compatibility. Note
# that any URI provided here limits HTTP/HTTPS access to that URI only.
#dbms.security.http_access_control_allow_origin=*

# Value of the HTTP Strict-Transport-Security (HSTS) response header. This header
# tells browsers that a webpage should only be accessed using HTTPS instead of HTTP.
# It is attached to every HTTPS response. Setting is not set by default so
# 'Strict-Transport-Security' header is not sent. Value is expected to contain
# directives like 'max-age', 'includeSubDomains' and 'preload'.
#dbms.security.http_strict_transport_security=

# Retention policy for transaction logs needed to perform recovery and backups.
dbms.tx_log.rotation.retention_policy=1 days

# Only allow read operations from this Neo4j instance. This mode still requires
# write access to the directory for lock purposes.
#dbms.read_only=false

# Comma separated list of JAX-RS packages containing JAX-RS resources, one
# package name for each mountpoint. The listed package names will be loaded
# under the mountpoints specified. Uncomment this line to mount the
# org.neo4j.examples.server.unmanaged.HelloWorldResource.java from
# neo4j-server-examples under /examples/unmanaged, resulting in a final URL of
# http://localhost:7474/examples/unmanaged/helloworld/{nodeId}
#dbms.unmanaged_extension_classes=org.neo4j.examples.server.unmanaged=/examples/unmanaged

# A comma separated list of procedures and user defined functions that are allowed
# full access to the database through unsupported/insecure internal APIs.
#dbms.security.procedures.unrestricted=my.extensions.example,my.procedures.*

# A comma separated list of procedures to be loaded by default.
# Leaving this unconfigured will load all procedures found.
#dbms.security.procedures.allowlist=apoc.coll.*,apoc.load.*,gds.*

#********************************************************************
# JVM Parameters
#********************************************************************

# G1GC generally strikes a good balance between throughput and tail
# latency, without too much tuning.
dbms.jvm.additional=-XX:+UseG1GC

# Have common exceptions keep producing stack traces, so they can be
# debugged regardless of how often logs are rotated.
dbms.jvm.additional=-XX:-OmitStackTraceInFastThrow

# Make sure that `initmemory` is not only allocated, but committed to
# the process, before starting the database. This reduces memory
# fragmentation, increasing the effectiveness of transparent huge
# pages. It also reduces the possibility of seeing performance drop
# due to heap-growing GC events, where a decrease in available page
# cache leads to an increase in mean IO response time.
# Try reducing the heap memory, if this flag degrades performance.
dbms.jvm.additional=-XX:+AlwaysPreTouch

# Trust that non-static final fields are really final.
# This allows more optimizations and improves overall performance.
# NOTE: Disable this if you use embedded mode, or have extensions or dependencies that may use reflection or
# serialization to change the value of final fields!
dbms.jvm.additional=-XX:+UnlockExperimentalVMOptions
dbms.jvm.additional=-XX:+TrustFinalNonStaticFields

# Disable explicit garbage collection, which is occasionally invoked by the JDK itself.
dbms.jvm.additional=-XX:+DisableExplicitGC

#Increase maximum number of nested calls that can be inlined from 9 (default) to 15
dbms.jvm.additional=-XX:MaxInlineLevel=15

# Disable biased locking
dbms.jvm.additional=-XX:-UseBiasedLocking

# Restrict size of cached JDK buffers to 256 KB
dbms.jvm.additional=-Djdk.nio.maxCachedBufferSize=262144

# More efficient buffer allocation in Netty by allowing direct no cleaner buffers.
dbms.jvm.additional=-Dio.netty.tryReflectionSetAccessible=true

# Exits JVM on the first occurrence of an out-of-memory error. Its preferable to restart VM in case of out of memory errors.
# dbms.jvm.additional=-XX:+ExitOnOutOfMemoryError

# Expand Diffie Hellman (DH) key size from default 1024 to 2048 for DH-RSA cipher suites used in server TLS handshakes.
# This is to protect the server from any potential passive eavesdropping.
dbms.jvm.additional=-Djdk.tls.ephemeralDHKeySize=2048

# This mitigates a DDoS vector.
dbms.jvm.additional=-Djdk.tls.rejectClientInitiatedRenegotiation=true

# Enable remote debugging
#dbms.jvm.additional=-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=*:5005

# This filter prevents deserialization of arbitrary objects via java object serialization, addressing potential vulnerabilities.
# By default this filter whitelists all neo4j classes, as well as classes from the hazelcast library and the java standard library.
# These defaults should only be modified by expert users!
# For more details (including filter syntax) see: https://openjdk.java.net/jeps/290
#dbms.jvm.additional=-Djdk.serialFilter=java.**;org.neo4j.**;com.neo4j.**;com.hazelcast.**;net.sf.ehcache.Element;com.sun.proxy.*;org.openjdk.jmh.**;!*

# Increase the default flight recorder stack sampling depth from 64 to 256, to avoid truncating frames when profiling.
dbms.jvm.additional=-XX:FlightRecorderOptions=stackdepth=256

# Allow profilers to sample between safepoints. Without this, sampling profilers may produce less accurate results.
dbms.jvm.additional=-XX:+UnlockDiagnosticVMOptions
dbms.jvm.additional=-XX:+DebugNonSafepoints

# Disable logging JMX endpoint.
dbms.jvm.additional=-Dlog4j2.disable.jmx=true

# Limit JVM metaspace and code cache to allow garbage collection. Used by cypher for code generation and may grow indefinitely unless constrained.
# Useful for memory constrained environments
#dbms.jvm.additional=-XX:MaxMetaspaceSize=1024m
#dbms.jvm.additional=-XX:ReservedCodeCacheSize=512m

#********************************************************************
# Wrapper Windows NT/2000/XP Service Properties
#********************************************************************
# WARNING - Do not modify any of these properties when an application
#  using this configuration file has been installed as a service.
#  Please uninstall the service before modifying this section.  The
#  service can then be reinstalled.

# Name of the service
dbms.windows_service_name=neo4j

#********************************************************************
# Other Neo4j system properties
#********************************************************************
#dbms.netty.ssl.provider=OPENSSL
#dbms.ssl.policy.https.trust_all=true
dbms.security.http_access_control_allow_origin=*
Run Cypher CREATE and MATCH queries
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