Add JSON schema to model dump.

doc/dump.schema

@@ -0,0 +1,55 @@
+{
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "definitions": {
+        "split_node": {
+            "type": "object",
+            "properties": {
+                "nodeid": {
+                    "type": "number",
+                    "minimum": 0
+                },
+                "depth": {
+                    "type": "number",
+                    "minimum": 0
+                },
+                "yes": {
+                    "type": "number",
+                    "minimum": 0
+                },
+                "no": {
+                    "type": "number",
+                    "minimum": 0
+                },
+                "split": {
+                    "type": "string"
+                },
+                "children": {
+                    "type": "array",
+                    "items": {
+                        "oneOf": [
+                            {"$ref": "#/definitions/split_node"},
+                            {"$ref": "#/definitions/leaf_node"}
+                        ]
+                    },
+                    "maxItems": 2
+                }
+            },
+            "required": ["nodeid", "depth", "yes", "no", "split", "children"]
+        },
+        "leaf_node": {
+            "type": "object",
+            "properties": {
+                "nodeid": {
+                    "type": "number",
+                    "minimum": 0
+                },
+                "leaf": {
+                    "type": "number"
+                }
+            },
+            "required": ["nodeid", "leaf"]
+        }
+    },
+    "type": "object",
+    "$ref": "#/definitions/split_node"
+}

src/tree/tree_model.cc

@@ -68,20 +68,20 @@ class TreeGenerator {
     return result;
   }
 
-  virtual std::string Indicator(RegTree const& tree, int32_t nid, uint32_t depth) {
+  virtual std::string Indicator(RegTree const& tree, int32_t nid, uint32_t depth) const {
     return "";
   }
-  virtual std::string Integer(RegTree const& tree, int32_t nid, uint32_t depth) {
+  virtual std::string Integer(RegTree const& tree, int32_t nid, uint32_t depth) const {
     return "";
   }
-  virtual std::string Quantitive(RegTree const& tree, int32_t nid, uint32_t depth) {
+  virtual std::string Quantitive(RegTree const& tree, int32_t nid, uint32_t depth) const {
     return "";
   }
-  virtual std::string NodeStat(RegTree const& tree, int32_t nid) {
+  virtual std::string NodeStat(RegTree const& tree, int32_t nid) const {
     return "";
   }
 
-  virtual std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) = 0;
+  virtual std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) const = 0;
 
   virtual std::string SplitNode(RegTree const& tree, int32_t nid, uint32_t depth) {
     auto const split_index = tree[nid].SplitIndex();
@@ -110,7 +110,7 @@ class TreeGenerator {
     return result;
   }
 
-  virtual std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) = 0;
+  virtual std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) const = 0;
   virtual std::string BuildTree(RegTree const& tree, int32_t nid, uint32_t depth) = 0;
 
  public:
@@ -181,7 +181,7 @@ class TextGenerator : public TreeGenerator {
   TextGenerator(FeatureMap const& fmap, std::string const& attrs, bool with_stats) :
       TreeGenerator(fmap, with_stats) {}
 
-  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     static std::string kLeafTemplate = "{tabs}{nid}:leaf={leaf}{stats}";
     static std::string kStatTemplate = ",cover={cover}";
     std::string result = SuperT::Match(
@@ -195,7 +195,7 @@ class TextGenerator : public TreeGenerator {
     return result;
   }
 
-  std::string Indicator(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string Indicator(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     static std::string const kIndicatorTemplate = "{nid}:[{fname}] yes={yes},no={no}";
     int32_t nyes = tree[nid].DefaultLeft() ?
                    tree[nid].RightChild() : tree[nid].LeftChild();
@@ -211,7 +211,7 @@ class TextGenerator : public TreeGenerator {
 
   std::string SplitNodeImpl(
       RegTree const& tree, int32_t nid, std::string const& template_str,
-      std::string cond, uint32_t depth) {
+      std::string cond, uint32_t depth) const {
     auto split_index = tree[nid].SplitIndex();
     std::string const result = SuperT::Match(
         template_str,
@@ -226,7 +226,7 @@ class TextGenerator : public TreeGenerator {
     return result;
   }
 
-  std::string Integer(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string Integer(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     static std::string const kIntegerTemplate =
         "{tabs}{nid}:[{fname}<{cond}] yes={left},no={right},missing={missing}";
     auto cond = tree[nid].SplitCond();
@@ -238,21 +238,21 @@ class TextGenerator : public TreeGenerator {
                          std::to_string(integer_threshold), depth);
   }
 
-  std::string Quantitive(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string Quantitive(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     static std::string const kQuantitiveTemplate =
         "{tabs}{nid}:[{fname}<{cond}] yes={left},no={right},missing={missing}";
     auto cond = tree[nid].SplitCond();
     return SplitNodeImpl(tree, nid, kQuantitiveTemplate, SuperT::ToStr(cond), depth);
   }
 
-  std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     auto cond = tree[nid].SplitCond();
     static std::string const kNodeTemplate =
         "{tabs}{nid}:[f{fname}<{cond}] yes={left},no={right},missing={missing}";
     return SplitNodeImpl(tree, nid, kNodeTemplate, SuperT::ToStr(cond), depth);
   }
 
-  std::string NodeStat(RegTree const& tree, int32_t nid) override {
+  std::string NodeStat(RegTree const& tree, int32_t nid) const override {
     static std::string const kStatTemplate = ",gain={loss_chg},cover={sum_hess}";
     std::string const result = SuperT::Match(
         kStatTemplate,
@@ -297,15 +297,15 @@ class JsonGenerator : public TreeGenerator {
   JsonGenerator(FeatureMap const& fmap, std::string attrs, bool with_stats) :
       TreeGenerator(fmap, with_stats) {}
 
-  std::string Indent(uint32_t depth) {
+  std::string Indent(uint32_t depth) const {
     std::string result;
     for (uint32_t i = 0; i < depth + 1; ++i) {
       result += "  ";
     }
     return result;
   }
 
-  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     static std::string const kLeafTemplate =
         R"L({ "nodeid": {nid}, "leaf": {leaf} {stat}})L";
     static std::string const kStatTemplate =
@@ -321,11 +321,11 @@ class JsonGenerator : public TreeGenerator {
     return result;
   }
 
-  std::string Indicator(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string Indicator(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     int32_t nyes = tree[nid].DefaultLeft() ?
                    tree[nid].RightChild() : tree[nid].LeftChild();
     static std::string const kIndicatorTemplate =
-        R"ID( "nodeid": {nid}, "depth": {depth}, "split": "{fname}", "yes": {yes}, "no": {no}})ID";
+        R"ID( "nodeid": {nid}, "depth": {depth}, "split": "{fname}", "yes": {yes}, "no": {no})ID";
     auto split_index = tree[nid].SplitIndex();
     auto result = SuperT::Match(
         kIndicatorTemplate,
@@ -337,8 +337,9 @@ class JsonGenerator : public TreeGenerator {
     return result;
   }
 
-  std::string SplitNodeImpl(RegTree const& tree, int32_t nid,
-                            std::string const& template_str, std::string cond, uint32_t depth) {
+  std::string SplitNodeImpl(RegTree const &tree, int32_t nid,
+                            std::string const &template_str, std::string cond,
+                            uint32_t depth) const {
     auto split_index = tree[nid].SplitIndex();
     std::string const result = SuperT::Match(
         template_str,
@@ -353,7 +354,7 @@ class JsonGenerator : public TreeGenerator {
     return result;
   }
 
-  std::string Integer(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string Integer(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     auto cond = tree[nid].SplitCond();
     const bst_float floored = std::floor(cond);
     const int32_t integer_threshold
@@ -367,7 +368,7 @@ class JsonGenerator : public TreeGenerator {
                          std::to_string(integer_threshold), depth);
   }
 
-  std::string Quantitive(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string Quantitive(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     static std::string const kQuantitiveTemplate =
         R"I( "nodeid": {nid}, "depth": {depth}, "split": "{fname}", )I"
         R"I("split_condition": {cond}, "yes": {left}, "no": {right}, )I"
@@ -376,7 +377,7 @@ class JsonGenerator : public TreeGenerator {
     return SplitNodeImpl(tree, nid, kQuantitiveTemplate, SuperT::ToStr(cond), depth);
   }
 
-  std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     auto cond = tree[nid].SplitCond();
     static std::string const kNodeTemplate =
         R"I( "nodeid": {nid}, "depth": {depth}, "split": {fname}, )I"
@@ -385,7 +386,7 @@ class JsonGenerator : public TreeGenerator {
     return SplitNodeImpl(tree, nid, kNodeTemplate, SuperT::ToStr(cond), depth);
   }
 
-  std::string NodeStat(RegTree const& tree, int32_t nid) override {
+  std::string NodeStat(RegTree const& tree, int32_t nid) const override {
     static std::string kStatTemplate =
         R"S(, "gain": {loss_chg}, "cover": {sum_hess})S";
     auto result = SuperT::Match(
@@ -529,7 +530,7 @@ class GraphvizGenerator : public TreeGenerator {
  protected:
   // Only indicator is different, so we combine all different node types into this
   // function.
-  std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string PlainNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     auto split = tree[nid].SplitIndex();
     auto cond = tree[nid].SplitCond();
     static std::string const kNodeTemplate =
@@ -563,7 +564,7 @@ class GraphvizGenerator : public TreeGenerator {
     return result;
   };
 
-  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) override {
+  std::string LeafNode(RegTree const& tree, int32_t nid, uint32_t depth) const override {
     static std::string const kLeafTemplate =
         "    {nid} [ label=\"leaf={leaf-value}\" {params}]\n";
     auto result = SuperT::Match(kLeafTemplate, {

tests/cpp/tree/test_tree_model.cc

@@ -151,6 +151,10 @@ TEST(Tree, DumpJson) {
 
   str = tree.DumpModel(fmap, false, "json");
   ASSERT_EQ(str.find("cover"), std::string::npos);
+
+
+  auto j_tree = Json::Load({str.c_str(), str.size()});
+  ASSERT_EQ(get<Array>(j_tree["children"]).size(), 2);
 }
 
 TEST(Tree, DumpText) {

tests/python/test_basic_models.py

@@ -325,7 +325,7 @@ def test_model_json_io(self):
         assert locale.getpreferredencoding(False) == loc
 
     @pytest.mark.skipif(**tm.no_json_schema())
-    def test_json_schema(self):
+    def test_json_io_schema(self):
         import jsonschema
         model_path = 'test_json_schema.json'
         path = os.path.dirname(
@@ -342,3 +342,35 @@ def test_json_schema(self):
         jsonschema.validate(instance=json_model(model_path, parameters),
                             schema=schema)
         os.remove(model_path)
+
+    @pytest.mark.skipif(**tm.no_json_schema())
+    def test_json_dump_schema(self):
+        import jsonschema
+
+        def validate_model(parameters):
+            X = np.random.random((100, 30))
+            y = np.random.randint(0, 4, size=(100,))
+
+            parameters['num_class'] = 4
+            m = xgb.DMatrix(X, y)
+
+            booster = xgb.train(parameters, m)
+            dump = booster.get_dump(dump_format='json')
+
+            for i in range(len(dump)):
+                jsonschema.validate(instance=json.loads(dump[i]),
+                                    schema=schema)
+
+        path = os.path.dirname(
+            os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+        doc = os.path.join(path, 'doc', 'dump.schema')
+        with open(doc, 'r') as fd:
+            schema = json.load(fd)
+
+        parameters = {'tree_method': 'hist', 'booster': 'gbtree',
+                      'objective': 'multi:softmax'}
+        validate_model(parameters)
+
+        parameters = {'tree_method': 'hist', 'booster': 'dart',
+                      'objective': 'multi:softmax'}
+        validate_model(parameters)