# Serialization Formats in Neptune Streams
<a name="streams-change-formats"></a>

Amazon Neptune uses two different formats for serializing graph-changes data to log streams, depending on whether the graph was created using Gremlin or SPARQL.

Both formats share a common record serialization format, as described in [Neptune Streams API Response Format](streams-using-api-reponse.md), that contains the following fields:
+ `commitTimestamp`   –   The time at which the commit for the transaction was requested, in milliseconds from the Unix epoch.
+ `eventId`   –   The sequence identifier of the stream change record.
+ `data`   –   The serialized Gremlin, SPARQL, or OpenCypher change record. The serialization formats of each record are described in more detail in the next sections.
+ `op`   –   The operation that created the change.

**Topics**
+ [PG\_JSON Change Serialization Format](#streams-change-formats-gremlin)
+ [SPARQL NQUADS Change Serialization Format](#streams-change-formats-sparql)

## PG\_JSON Change Serialization Format
<a name="streams-change-formats-gremlin"></a>

**Note**  
The Gremlin stream output format (`GREMLIN_JSON`) output by the Gremlin stream endpoint (`https://{{Neptune-DNS}}:8182/gremlin/stream`) is deprecated. It is replaced by PG\_JSON, which is currently identical to `GREMLIN_JSON`.

A Gremlin or openCypher change record, contained in the `data` field of a log stream response, has the following fields:
+ `id` – String, required.

  The ID of the Gremlin or openCypher element.
+ `type` – String, required.

  The type of this Gremlin or openCypher element. Must be one of the following:
  + `vl` – Vertex label for Gremlin; node label for openCypher.
  + `vp` – Vertex properties for Gremlin; node properties for openCypher.
  + `e` – Edge and edge label for Gremlin; relationship and relationship type for openCypher.
  + `ep` – Edge properties for Gremlin; relationship properties for openCypher.
+ `key` – String, required.

  The property name. For element labels, this is "label".
+ `value` – `value` object, required.

  This is a JSON object that contains a `value` field for the value itself, and a `datatype` field for the JSON data type of that value.

  ```
    "value": {
      "value": "{{the new value}}",
      "dataType": "{{the JSON datatype of the new value}}"
    }
  ```
+ `from` – String, optional.

  If this is an edge (type="e"), the ID of the corresponding *from* vertex or source node.
+ `to` – String, optional.

  If this is an edge (type="e"), the ID of the corresponding *to* vertex or target node.

**Gremlin Examples**
+ The following is an example of a Gremlin vertex label.

  ```
  {
    "id": "{{an ID string}}",
    "type": "vl",
    "key": "label",
    "value": {
      "value": "{{the new value of the vertex label}}",
      "dataType": "String"
    }
  }
  ```
+ The following is an example of a Gremlin vertex property.

  ```
  {
    "id": "{{an ID string}}",
    "type": "vp",
    "key": "{{the property name}}",
    "value": {
      "value": "{{the new value of the vertex property}}",
      "dataType": "{{the datatype of the vertex property}}"
    }
  }
  ```
+ The following is an example of a Gremlin edge.

  ```
  {
    "id": "{{an ID string}}",
    "type": "e",
    "key": "label",
    "value": {
      "value": "{{the new value of the edge}}",
      "dataType": "String"
    },
    "from": "{{the ID of the corresponding "from" vertex}}",
    "to": "{{the ID of the corresponding "to" vertex}}"
  }
  ```

**openCypher Examples**
+ The following is an example of an openCypher node label.

  ```
  {
    "id": "{{an ID string}}",
    "type": "vl",
    "key": "label",
    "value": {
      "value": "{{the new value of the node label}}",
      "dataType": "String"
    }
  }
  ```
+ The following is an example of an openCypher node property.

  ```
  {
    "id": "{{an ID string}}",
    "type": "vp",
    "key": "{{the property name}}",
    "value": {
      "value": "{{the new value of the node property}}",
      "dataType": "{{the datatype of the node property}}"
    }
  }
  ```
+ The following is an example of an openCypher relationship.

  ```
  {
    "id": "{{an ID string}}",
    "type": "e",
    "key": "label",
    "value": {
      "value": "{{the new value of the relationship}}",
      "dataType": "String"
    },
    "from": "{{the ID of the corresponding source node}}",
    "to": "{{the ID of the corresponding target node}}"
  }
  ```

## SPARQL NQUADS Change Serialization Format
<a name="streams-change-formats-sparql"></a>

Neptune logs changes to SPARQL quads in the graph using the Resource Description Framework (RDF) `N-QUADS` language defined in the [W3C RDF 1.1 N-Quads](https://www.w3.org/TR/n-quads/) specification.

The `data` field in the change record simply contains a `stmt` field that holds an N-QUADS statement expressing the changed quad, as in the following example.

```
  "stmt" : "<https://test.com/s> <https://test.com/p> <https://test.com/o> .\n"
```