Add api-ref doc for data model api

Change-Id: I7d2203f35623ac6b0649ba5d99a04e9d6ca4430f

api-ref/source/watcher-api-v1-datamodel.inc

@@ -0,0 +1,55 @@
+.. -*- rst -*-
+
+==========
+Data Model
+==========
+
+``Data Model`` is very important for Watcher to generate resource
+optimization solutions. Users can easily view the data model by the
+API.
+
+
+List Data Model
+===============
+
+.. rest_method::  GET /v1/data_model
+
+Returns the information about Data Model.
+
+Normal response codes: 200
+
+Error codes: 400,401
+
+Request
+-------
+
+.. rest_parameters:: parameters.yaml
+
+   - audit: r_audit
+   - type: r_type
+
+Response
+--------
+
+.. rest_parameters:: parameters.yaml
+
+    - server_uuid: server_uuid
+    - server_name: server_name
+    - server_vcpus: server_vcpus
+    - server_memory: server_memory
+    - server_disk: server_disk
+    - server_state: server_state
+    - node_uuid: node_uuid
+    - node_hostname: node_hostname
+    - node_vcpus: node_vcpus
+    - node_vcpu_ratio: node_vcpu_ratio
+    - node_memory: node_memory
+    - node_memory_ratio: node_memory_ratio
+    - node_disk: node_disk
+    - node_disk_ratio: node_disk_ratio
+    - node_state: node_state
+
+**Example JSON representation of a Data Model:**
+
+.. literalinclude:: samples/datamodel-list-response.json
+   :language: javascript