[Doc] Add docs for ProtobufNative Schema

site2/docs/schema-understand.md

@@ -198,29 +198,31 @@ Currently, Pulsar supports the following complex types:
 | Complex Type | Description |
 |---|---|
 | `keyvalue` | Represents a complex type of a key/value pair. |
-| `struct` | Supports **AVRO**, **JSON**, and **Protobuf**. |
+| `struct` | Handles structured data. It supports `AvroBaseStructSchema` and `ProtobufNativeSchema`. |
 
 #### keyvalue
 
 `Keyvalue` schema helps applications define schemas for both key and value. 
 
 For `SchemaInfo` of `keyvalue` schema, Pulsar stores the `SchemaInfo` of key schema and the `SchemaInfo` of value schema together.
 
-Pulsar provides two methods to encode a key/value pair in messages：
+Pulsar provides the following methods to encode a key/value pair in messages：
 
 * `INLINE`
 
 * `SEPARATED`
 
-Users can choose the encoding type when constructing the key/value schema.
+You can choose the encoding type when constructing the key/value schema.
 
-##### INLINE
+<!--DOCUSAURUS_CODE_TABS-->
 
-Key/value pairs will be encoded together in the message payload.
+<!--INLINE-->
 
-##### SEPARATED
+Key/value pairs are encoded together in the message payload.
 
-Key will be encoded in the message key and the value will be encoded in the message payload. 
+<!--SEPARATED-->
+
+Key is encoded in the message key and the value is encoded in the message payload. 
 
 **Example**
 
@@ -287,25 +289,36 @@ This example shows how to construct a key/value schema and then use it to produc
     KeyValue<Integer, String> kv = msg.getValue();
     ```
 
+<!--END_DOCUSAURUS_CODE_TABS-->
+
 #### struct
 
-Pulsar uses [Avro Specification](http://avro.apache.org/docs/current/spec.html) to declare the schema definition for `struct` schema. 
+This section describes the details of type and usage of the `struct` schema.
 
-This allows Pulsar:
+##### Type
 
-* to use same tools to manage schema definitions
+`struct` schema supports `AvroBaseStructSchema` and `ProtobufNativeSchema`.
 
-* to use different serialization/deserialization methods to handle data
+|Type|Description|
+---|---|
+`AvroBaseStructSchema`|Pulsar uses [Avro Specification](http://avro.apache.org/docs/current/spec.html) to declare the schema definition for `AvroBaseStructSchema`, which supports  `AvroSchema`, `JsonSchema`, and `ProtobufSchema`. <br><br>This allows Pulsar:<br>- to use the same tools to manage schema definitions<br>- to use different serialization or deserialization methods to handle data|
+`ProtobufNativeSchema`|`ProtobufNativeSchema` is based on protobuf native Descriptor. <br><br>This allows Pulsar:<br>- to use native protobuf-v3 to serialize or deserialize data<br>- to use `AutoConsume` to deserialize data.
 
-There are two methods to use `struct` schema：
+##### Usage
+
+Pulsar provides the following methods to use the `struct` schema:
 
 * `static`
 
 * `generic`
 
-##### static
+* `SchemaDefinition`
+
+<!--DOCUSAURUS_CODE_TABS-->
 
-You can predefine the `struct` schema, and it can be a POJO in Java, a `struct` in Go, or classes generated by Avro or Protobuf tools. 
+<!--static-->
+
+You can predefine the `struct` schema, which can be a POJO in Java, a `struct` in Go, or classes generated by Avro or Protobuf tools. 
 
 **Example** 
 
@@ -334,7 +347,7 @@ Pulsar gets the schema definition from the predefined `struct` using an Avro lib
     User user = consumer.receive();
     ```
 
-##### generic
+<!--generic-->
 
 Sometimes applications do not have pre-defined structs, and you can use this method to define schema and access data.
 
@@ -360,6 +373,39 @@ You can define the `struct` schema using the `GenericSchemaBuilder`, generate a
                 .build()).send();
     ```
 
+<!--SchemaDefinition-->
+
+You can define the `schemaDefinition` to generate a `struct` schema.
+
+**Example** 
+
+1. Create the _User_ class to define the messages sent to Pulsar topics.
+
+    ```java
+    public class User {
+        String name;
+        int age;
+    }
+    ```
+
+2. Create a producer with a `SchemaDefinition` and send messages.
+
+    ```java
+    SchemaDefinition<User> schemaDefinition =   SchemaDefinition.builder().withPojo(User.class).build();
+    Producer<User> producer = client.newProducer(schemaDefinition).create();
+    producer.newMessage().value(User.builder().userName("pulsar-user").userId(1L).build()).send();
+    ```
+
+3. Create a consumer with a `SchemaDefinition` schema and receive messages
+
+    ```java
+    SchemaDefinition<User> schemaDefinition = SchemaDefinition.builder().withPojo(User.class).build();
+    Consumer<User> consumer = client.newConsumer(schemaDefinition).subscribe();
+    User user = consumer.receive();
+    ```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
+
 ### Auto Schema
 
 If you don't know the schema type of a Pulsar topic in advance, you can use AUTO schema to produce or consume generic records to or from brokers.
@@ -399,7 +445,7 @@ pulsarProducer.produce(kafkaMessageBytes);
 
 `AUTO_CONSUME` schema helps a Pulsar topic validate whether the bytes sent by a Pulsar topic is compatible with a consumer, that is, the Pulsar topic deserializes messages into language-specific objects using the `SchemaInfo` retrieved from broker-side. 
 
-Currently, `AUTO_CONSUME` only supports **AVRO** and **JSON** schemas. It deserializes messages into `GenericRecord`.
+Currently, `AUTO_CONSUME` supports AVRO, JSON and ProtobufNativeSchema schemas. It deserializes messages into `GenericRecord`.
 
 **Example**