Building a Neo4j Reporting Service Part II

It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.

Sir Arthur Conan Doyle, Author of Sherlock Holmes stories

A Subgraph From Neo4j's Browser

Just as Sir Arthur Conan Doyle's character, Sherlock Holmes, manically collects facts and evidence to prove theories, we find ourselves doing much of the same today except on a much larger scale— web scale. The web is an ever growing expanse of facts and evidence. It is at our disposal to observe without much of a challenge, but to store it and retrieve it in a way that answers the big questions, that's challenging.

Continuing on from Building a Graph-based Reporting Platform: Part I, I posed some questions related to understanding how to build great community experiences around Neo4j using Meetup.com for local events. I presented an idea to use Neo4j to build a platform that could help us understand the demand for presenting compelling content at events.

Compelling content is at the core of great community experiences. That content fuels the conversations between people, ideas begin to flow, and innovation is born.

My idea was to build an open-source platform that would poll public APIs, translate collected data into a graph, and store it in a graph database to be analyzed, queried, and visualized over time. The first component of this architecture is the Data Import Scheduler, which this post describes in detail.

Polling Data From Public APIs

Let's start out by answering a basic question.

What does the data import scheduler do?

The analytics data import scheduler is a Node.js process that can be hosted for free on Heroku and is responsible for collecting time-based statistics from a public API. In this case, the Meetup.com REST API exposes a set of methods that provide a momentary snapshot into the number of members that a group has at the time of the request. The data import scheduler polls this endpoint once a day to retrieve Meetup group statistics to later be used for time-based analysis from our graph database, Neo4j.

As illustrated in the diagram below, the Node.js application wakes up once a day and checks in with the Meetup.com REST API.

The scheduler process polls Meetup.com's REST API daily. An HTTP GET request is dispatched for each city we're tracking, returning a JSON formatted response for groups in those cities. The JSON data for each group is then translated into a subgraph, formatted as Neo4j's Cypher query language. The Cypher query is then sent as a transaction to Neo4j and updates a snapshot of the group's stats for that day.

Importing a Meetup Group's Subgraph

The image below is a visualization of a Meetup group's subgraph, translated from JSON data polled on an arbitrary date.

Graph Database - San Francisco on 4/28/2014

We see that the group has a set of topic nodes, which may already exist within the database. The subgraph must be merged into the larger graph without duplicating any nodes. Using Cypher's MERGE clause we can get or create nodes, which is useful for expanding our graph's connected data. Each topic will collect more groups as new subgraphs are merged for daily imports. The same is also true for both day and location nodes.

After a few days of scheduled imports, a group's subgraph begins to take shape. As day nodes are connected to the previous day's node, membership statistics are connected.

A Meetup Group Statistics Subgraph, 4/23 to 4/28

The data import scheduler application is open-source and available on GitHub. Also, full documentation is available to help you get started with customizing your own graph-based reporting platform.

All analysis on the temporal stats collected from the data import scheduler is performed within the REST API module of the reporting platform. It also safely exposes the graph database to a front-end web dashboard, consumed from client-side JavaScript. The REST API uses Swagger, which is a specification and complete framework for describing, producing, consuming, and visualizing RESTful web services.

• Building a Graph-based Reporting Platform: Part I
• Meetup Analytics API Demo
• Meetup Analytics Web Dashboard Demo
• Meetup Reporting GitHub Repository

Building a Neo4j Reporting Service Part I

Data science is pretty hot right now. The obvious reason is that data is rapidly expanding in complexity and size. There is an opportunity to be had in building systems that can capture this data, classify it in multiple dimensions, and to scale it up to the demands of analysts looking to convert data into valuable reports.

As a developer evangelist for Neo4j, I am frequently out in the community talking about things I build using our database. We use Meetup.com to schedule and promote our community events all over the world.

If you're unfamiliar with Meetup.com, here is a description from their Wikipedia entry:

"Meetup is an online social networking portal that facilitates offline group meetings in various localities around the world. Meetup allows members to find and join groups unified by a common interest, such as politics, books, games, movies, health, pets, careers or hobbies. Users enter their postal code or their city and the topic they want to meet about, and the website helps them arrange a place and time to meet. Topic listings are also available for users who only enter a location."

At Neo4j, we're obsessed with data, especially connected data. We believe in our product because we use it to solve our own problems every day. With something like Meetup.com, we found ourselves guessing about many of the aspects of our community and how we could do a better job creating a great community experience.

Some of those questions were:

• How many people will show up to an event from the attendee list?

• What kind of content are people interested in hearing about?

• What's the best location to host our meetups to boost attendance?

I wanted to use Neo4j to do reporting. I decided to put together a platform to track some of this information and build some reports to visualize the data we collected. I started by breaking down the problem into a set of stories to be implemented as a report.

Problem

• Track meetup group growth over time
  
• Apply tags to meetup groups and report combined growth of all groups over time
  

Questions

• Given a start date and an end date, what is the time series that plots the membership growth of a given meetup group?
  
• Given a start date, an end date, and a combination of tags, what is the time series that plots the combined membership growth of all meetup groups with those tags?
  
• How do you generate the JSON data of a time series for a basic JS line chart plugin?
  

I decided to start with a GraphGist, which is an open source project we built to enable our community to put together a quick proof of concept using our database.

Neo4j for Graph Analytics: Meetup.com Example

I designed an example graph data model, which I then translated into Neo4j's Cypher query language to create an example dataset.

Now it was time to scale it up to a full platform. I decided to use Node.js.

There would be three Node.js driven components. One console application for importing data on a schedule and two web applications; a dashboard for displaying reports and REST API to communicate with the Neo4j graph database.

With an architecture in place, I went forward with building out each of the modules.

In my next blog post I will go through the details of building the import scheduler, which polls the Meetup.com API each day and imports the graph data model into Neo4j.

Feel free to take a look at the finished documentation which details the creation of each of the Node.js modules:

Graph-based Reporting Documentation

Also, I put a slide deck together:

Building a Graph-based Reporting Platform from Kenny Bastani