The primary key structure for the table. Each KeySchemaElement consists of:
AttributeName - The name of the attribute. KeyType - The role of the attribute: HASH - partition key RANGE - sort key The partition key of an item is also known as its hash attribute. The
term "hash attribute" derives from DynamoDB' usage of an internal hash function to evenly distribute data items across partitions, based on their partition key values.
The sort key of an item is also known as its range attribute. The term "range attribute" derives from the way DynamoDB stores items with the same partition key physically close together, in sorted order by the sort key value.
For more information about primary keys, see Primary Key (http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DataModel.html#DataModelPrimaryKey)
in the Amazon DynamoDB Developer Guide.