Understanding schemas

A schema is a way of describing a nested structure of a Java object. A typical Java object contains fields that have string names and data types.

Let's see the following Java class:

public class Position {
  double latitude; 
  double longitude;
}

This class has two fields called latitude and longitude, respectively, both of which are of the double type. The matching Schema property of this class would be as follows:

Position: Row
  latitude: double
  longitude: double

This notation declared a Position type with a schema of the Row type containing two fields, latitude and longitude, both of the double type. A Row is one of Apache Beam's built-in schema types with a nested structure – the others are Array, Iterable, and Map with their usual definitions in computer science. The difference between Array and Iterable is that Iterable does not have a known size until it's iterated over. This...