In this project, ETL pipeline is build on data warehouse hosted on AWS Redshift. The data is loaded from S3 to stagging tables on Redshift and SQL queries are written to create analytics tables from staging tables.

The dataset is composed of two files the Songs data and Logs data that is present in S3 bucket.

The song data is dataset with million of entries. Each file is in JSON format that contains the data about song, artist of that song. Moreover, the files are partitioned by the first three letters of song ID. The single entry of the song dataset looks like

• {
     "num_songs":1,
     "artist_id":"ARJIE2Y1187B994AB7",
     "artist_latitude":null,
     "artist_longitude":null,
     "artist_location":"",
     "artist_name":"Line Renaud",
     "song_id":"SOUPIRU12A6D4FA1E1",
     "title":"Der Kleine Dompfaff",
     "duration":152.92036,
     "year":0
  }
  

The second dataset consists of log files in JSON format generated by this event simulator based on the songs in the dataset above. These simulate app activity logs from an imaginary music streaming app based on configuration settings.

The logs dataset is also in the JSON formatted, which is formed by the event simulator based on the songs dataset. The logs dataset is the activity logs from the music app.

• {
      "artist": "Pavement",
      "auth": "Logged in",
      "firstName": "Sylvie",
      "gender": "F",
      "iteminSession": 0,
      "lastName": "Cruz",
      "length": 99.16036,
      "level": "free",
      "location": "Kiamath Falls, OR",
      "method": "PUT",
      "page": "NextSong",
      "registration": 1.540266e+12,
      "sessionId": 345,
      "song": "Mercy: The Laundromat",
      "status": 200,
      "ts": 1541990258796,
      "userAgent": "Mozzilla/5.0...",
      "userId": 10
  }
  

There are two staging tables: Event table: artist VARCHAR, auth VARCHAR, firstName VARCHAR, gender VARCHAR, itemInSession INT, lastName VARCHAR, length DOUBLE PRECISION, level VARCHAR, location VARCHAR, method VARCHAR , page VARCHAR, registration VARCHAR, sessionid INT, song VARCHAR, status INT, ts VARCHAR, userAgent VARCHAR, userId INT*

Song table* num_songs INTEGER,* artist_id VARCHAR, artist_latitude VARCHAR, artist_longitude VARCHAR, artist_location VARCHAR , artist_name VARCHAR, song_id VARCHAR, title VARCHAR, duration NUMERIC NOT NULL, year integer*

These staging tables helps forming dimension tables and fact tables:

*user_id, first_name, last_name, gender, level*

*song_id, title, artist_id, year, duration*

*artist_id, name, location, latitude, longitude*

*start_time, hour, day, week, month, year, weekday*

*songplay_id, start_time, user_id, level, song_id, artist_id, session_id, location, user_agent*

All the tables contains Primary Key as there should be something unique to identify the rows in the table.

The ETL process is comprises of two steps:

• Getting data from S3 bucket to staging table
• Insert the data in dimension and fact table from staging tables using Star Schema

- create_tables.py: When create_tables.py run, it will first create tables and drop if table already exists. 
- etl.py: read and process data files
- dwh.cfg: File contains the data warehouse settings for AWS. It contains CLUSTER, IAM_ROLE and S3 settings for the ETL pipeline
- sql_queries: Contains the sql queries for dropping, creation, selection data from tables.