To use Snowplow successfully, you need to have a good idea of:
- What events you care about in your business
- What events occur in your website / mobile application / server side systems / factories / call centers / dispatch centers / etc
- What decisions you make based on those events
- What you need to know about those events to make those decisions
That’s where event dictionary comes into play. It is a document that defines the universe of events that a company is interested in tracking. For each event, it defines:
- What the event is (often this might be illustrated e.g. with screenshots)
- What data is captured when the event occurs, that represents the event. This is a data structure for the event.
- Details on how the relevant Snowplow tracker has been setup to pass the event data into Snowplow.
We use a schema registry to store these definitions.
Schema registry provides a serving layer for your metadata. It provides a RESTful interface for storing and retrieving schemas. It stores a versioned history of all schemas and allows evolution of schemas.
When an event occurs, it generally involves a number of entities, and takes place in a particular setting.
An entity is the group of entities associated with or describing the setting in which an event has taken place.
Due to the nature of custom (as well as Snowplow authored) events/entities there has to be some mechanism in place ensuring validity of the captured data.
JSON schema plays a significant part in this mechanism. Both events and entities have schemas which define what data is recorded about the event, or entity, at data capture time.
JSON schema specifies a JSON-based format to define the structure of JSON data for validation, documentation, and interaction control.
Snowplow requires that you put together schemas for your events and entities, ahead of data collection time. It then uses those schemas to process the data, in particular:
- To validate that the data coming in is “good data” that conforms to the schema
- Process the data correctly, in particular, shredding the JSONs that represent the data into tidy tables in Redshift suitable for analysis
Iglu is a key technology for making this possible. It is machine-readable, open-source schema registry for JSON and Thrift schemas from the team at Snowplow Analytics. A schema registry is like Git but holds data schemas instead of software or code.