Basic concepts of neo4j graph database

brief introduction ： This paper takes the movie diagram as an example , explain neo4j Figure basic concepts in database

Movie diagram

The circle in the following figure represents three nodes （node）, Each node has a label representing the category （label） And attribute （properties）, Such as ：name、born、title、released, Nodes are connected by one-way arrows to represent the relationship between nodes （relationships）, Such as ：ACTED_IN、DIRECTED

following Cycher Statement to generate the above graph structure

CREATE (:Person:Actor {name: 'Tom Hanks', born: 1956})-[:ACTED_IN {roles: ['Forrest']}]->(:Movie {title: 'Forrest Gump'})<-[:DIRECTED]-(:Person {name: 'Robert Zemeckis', born: 1951})

node node

Each circle in the movie graph represents a node （node）, Each node represents an entity , The first node is analyzed in detail below

Nodes in the Person、Actor For node label （label）, Nodes with the same label can be divided into the same class , Be similar to Java The concept of middle class . A node can have multiple labels , The relationship between tags is similar to that between classes （ Inherit ）, In this node Actor It can be seen as Person Subclasses of ;

name:'Tom Hanks' born:1956 For node attribute （properties）, Be similar to Java Properties in a class

java The implementation code is as follows

public class Person{
    
    String name;
    long born;
}
class Actor extends Person{
    }

This node can be composed of the following Cypher Statements generated

CREATE (:Person:Actor {name: 'Tom Hanks', born: 1956})

Statements explain ：

1. Create the label to which the node belongs :Person、:Actor
2. Pair with key value （key-value pairs） Declare attributes in the form of , And braces {} Include

Relationship relationship

Describe how interconnected start and end nodes are related （describes how a connection between a source node and a target node are related）, Relationships can make nodes into linked lists （list）、 Trees （tree）、 chart （map）、 Composite entities .

characteristic ：

1. Directional and unidirectional
2. There must be a type （type） To define what kind of relationship
   Must have a type (one type) to define (classify) what type of relationship it is.
3. Nodes can be represented by relationships that point to themselves
4. Relationships can have attributes

The type of relationship shown in the figure above （type） yes ACTED_IN, The attribute is roles: ['Forrest']、performance: 5

Cypher Statement for ：

CREATE ()-[:ACTED_IN {roles: ['Forrest'], performance: 5}]->()

() Representation node

-[:ACTED_IN {roles: ['Forrest'], performance: 5}]-> Is a statement that declares a relationship , Key value pairs also represent attributes （properties）

attribute properties

Attributes describe nodes in the form of key value pairs （node） And relationship （relationships） The data of

Attributes can be of various data types , Such as ：number、string or boolean; It can be used to store similar data array or list, Such as ：strings、numbers、bollean values

CREATE (:Example {a: 1, b: 3.14})  //  attribute a Storage integer Type value 1, attribute b Storage float Data of type 
CREATE (:Example {c: 'This is an example string', d: true, e: false})
CREATE (:Example {f: [1, 2, 3], g: [2.71, 3.14], h: ['abc', 'example'], i: [true, true, false]})

Other concepts

Other concepts in the figure database will not be detailed for the time being , Such as ：Traversals（ Traverse ）、paths（ route ）、Schema、Indexes（ Indexes ）、Constraints（ constraint ）

Add

The movie database is neo4j The official example of , You can use :guide movie-graph Command view . About attributes 、 Concepts such as tags can be verified and understood with the help of the following query statements .

Match (n) 
return ID(n) as id, properties(n) AS properties, labels(n) AS label

neo4j Naming conventions in

Label of the node 、 The type of relationship 、 Attributes are case sensitive , for example ： attribute name≠Name, For a moment neo4j Officially recommended naming conventions

Graph entity	Recommended style	Example
Node label	Camel case, beginning with an upper-case character	:VehicleOwner rather than :vehice_owner
Relationship type	Upper case, using underscore to separate words	:OWNS_VEHICLE rather than :ownsVehicle
Property	Lower camel case, beginning with a lower-case character	firstName rather than first_name

Comparative graph theory

In graph theory , Nodes are also called vertices （vertices ） Or point （point）
Relationships are also called edges （edges）、 link （links） Or line （lines）

Create nodes

The syntax for creating nodes , You can name the node n. Because the node name is not used as a unique identifier , Similar to temporary variables , Using the same node name does not affect the creation of the database

CREATE (n:Person {name:'Sally'}) RETURN n
CREATE (n:Person {name:'Steve'}) RETURN n
CREATE (n:Person {name:'Mike'}) RETURN n

neo4j Image export

If exported as svg, You can use vscode or notepad Edit content , lookup font-size Set font size , lookup font-family Set the font format , And then use photoshop take svg Export to png Or with the help of online transfer png Website

neo4j Interactive settings

Click on any node , A gray circle appears , Respectively represent the position of the fixed node 、 Hide nodes 、 Display other nodes related to this node

Click the tab of the node on the right Person, You can adjust the color and size of nodes

Click on the arrow , You can set the thickness and color of the arrows representing the relationship

---

Reference article ：

meo4j 4.4 Official documents Graph database concepts

Neo4j Figure Chinese document of database —neo4j 0.1.0a documentation

be based on Neo4j Build a movie map - You know (zhihu.com)

neo4j Figure database node name 、 Tag name 、 Property name - Simple books (jianshu.com)

neo4j Export high definition pictures and adjust Fonts - You know (zhihu.com)