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@@ -9,20 +9,37 @@ created: Sunday, June 09, 2024
 
 ## Data structure
 
+### Non-relational tables
+
 DynamoDB is "NoSQL" because it does not support #SQL queries and is
 non-relational meaning there cannot be JOIN operations via
 [foreign_keys](Foreign_keys_in_SQL.md)
 
 ![](../img/dynamodb.png)
 
-Although the data is stored as a table, one of the attributes is a key and the
-rest of the attributes are effectively the values associated with it. Each item
-in the table is uniquely identifiable by its primary key.
+### Primary key
+
+Although the data is stored as a table, one of the attributes is a primary key
+and the rest of the attributes are effectively the values associated with it.
 
 Because DynamoDB is schemaless, neither the attributes or their data types need
 to be defined beforehand and each item can have its own distinct attributes.
 
-This attribute is known as the primary key.
+Each item in the table is uniquely identifiable by its primary key.
+
+There are two types of primary key available:
+
+- partition key: a simple primary key composed of one attribute only. Because
+  the primary key is hash-mapped items can be retrieved very rapidly using the
+  primary key.
+
+- composite key: this comprises a partition key and a _sort key_ both of which
+  are attributes
+
+However, you can also set one or more **secondary indices**. A secondary index
+lets you query the data in the table using an alternate key, in addition to
+queries against the primary key. DynamoDB doesn't require that you use indexes,
+but they give your applications more flexibility when querying your data.
 
 ## Usage