Graph Database Neo4j: Part I

What are graph databases? Liitle refresher on Graph Theory (Refer Wiley book on graphs)

A Graph Database stores data in a Graph, the most generic of data structures, capable of elegantly representing any kind of data in a highly accessible way. The records in a graph database are called Nodes. Nodes are connected through typed, directed arcs, called Relationships. Each node and relationship can have named attributes referred to as Properties. A Label is a name that organizes nodes into groups.

In Neo4j, a node can be simply represented as (a) or (), for an empty node. It is not mandatory that nodes should be connected. The real advantage is to build relationships between nodes, (arcs in graph theory).

A relationship can be represented as (a)-->(b)/(a)-->()

We can query the graph database to find out matching of patterns by defining relationships. for example, if we want to know with whom all node ‘x’ has relationships with, then we can query (x)-[r]->()

If node ‘x’ has many types of relationships like worked in this company, acted in the movie, etc… we can retreive that in our query by asking, (a)-[:WORKED_AT]->(c)

We can also query with labels. Imagine Label is like a node’s property. If multiple nodes have same property, then we can group them. For example, if we have many nodes with labels like man, woman, American, British, then we can group them as American women, British women, etc…

For example,

(a:man {citizen:"American"}) list of American men in our database

(a:woman {citizen:"British"})->[WORKED_AT]->(c:ORC Solutions)

list of British women worked at ORC Solutions Pvt Ltd (just an example)

So What is Neo4j really?

Neo4j is a one of the NoSQL databases whose data model is a Graph, specifically a Property Graph. Cypher is Neo4j’s graph query language (SQL for graphs or GQL). It is a declarative query language where we can describe what we are interested in, not how it is acquired. Supposedly very readable and expressive.