diff --git a/tests/test_core.py b/tests/test_core.py
index 688eca6..fa40524 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -24,7 +24,7 @@ def ds():
     ds = xr.Dataset(
         {
             'x': xr.DataArray(np.arange(4) - 2, dims='x'),
-            'foo': xr.DataArray(np.ones(4, dtype='i4'), dims='x'),
+            'foo': xr.DataArray(np.ones(4, dtype='i4'), dims='x', attrs=dict(units='K')),
             'bar': xr.DataArray(np.arange(8, dtype=np.float32).reshape(4, 2), dims=('x', 'y')),
         }
     )
@@ -222,29 +222,50 @@ def test_dataset_empty_constructor():
 
 def test_dataset_example(ds):
     ds_schema = DatasetSchema(
-        {
-            'foo': DataArraySchema(name='foo', dtype=np.int32, dims=['x']),
+        data_vars={
+            'foo': DataArraySchema(
+                name='foo',
+                dtype=np.int32,
+                dims=['x'],
+                attrs=AttrsSchema(attrs=dict(units=AttrSchema(value='K')))
+            ),
             'bar': DataArraySchema(name='bar', dtype=np.floating, dims=['x', 'y']),
-        }
+        },
+        coords={'x': DataArraySchema(name='x', dtype=np.int64, dims=['x'])},
+<<<<<<< HEAD
+=======
+        attrs={},
+>>>>>>> d3ba8807e2b69a26a98521c8ee927a13df0f0a5a
     )
 
     jsonschema.validate(ds_schema.json, ds_schema._json_schema)
 
     assert list(ds_schema.json['data_vars'].keys()) == ['foo', 'bar']
+    assert list(ds_schema.json['coords']['coords'].keys()) == ['x']
     ds_schema.validate(ds)
 
-    ds['foo'] = ds.foo.astype('float32')
+    ds2 = ds.copy()
+    ds2['foo'] = ds2.foo.astype('float32')
     with pytest.raises(SchemaError, match='dtype'):
-        ds_schema.validate(ds)
+        ds_schema.validate(ds2)
 
-    ds = ds.drop_vars('foo')
+    ds2 = ds2.drop_vars('foo')
     with pytest.raises(SchemaError, match='variable foo'):
-        ds_schema.validate(ds)
+        ds_schema.validate(ds2)
+
+    ds3 = ds.copy()
+    ds3['x'] = ds3.x.astype('float32')
+    with pytest.raises(SchemaError, match='dtype'):
+        ds_schema.validate(ds3)
+
+    ds3 = ds3.drop_vars('x')
+    with pytest.raises(SchemaError, match='coords has missing keys'):
+        ds_schema.validate(ds3)
 
     # json roundtrip
     rt_schema = DatasetSchema.from_json(ds_schema.json)
     assert isinstance(rt_schema, DatasetSchema)
-    rt_schema.json == ds_schema.json
+    assert rt_schema.json == ds_schema.json
 
 
 def test_checks_ds(ds):
@@ -271,7 +292,7 @@ def test_dataset_with_attrs_schema():
     expected_value = 'expected_value'
     actual_value = 'actual_value'
     ds = xr.Dataset(attrs={name: actual_value})
-    ds_schema = DatasetSchema(attrs={name: AttrSchema(value=expected_value)})
+    ds_schema = DatasetSchema(dict(attrs={name: AttrSchema(value=expected_value)}))
     jsonschema.validate(ds_schema.json, ds_schema._json_schema)
 
     ds_schema_2 = DatasetSchema(attrs=AttrsSchema({name: AttrSchema(value=expected_value)}))
diff --git a/xarray_schema/components.py b/xarray_schema/components.py
index d212ddc..e56f71f 100644
--- a/xarray_schema/components.py
+++ b/xarray_schema/components.py
@@ -396,13 +396,12 @@ def __init__(
 
     @classmethod
     def from_json(cls, obj: dict):
-        attrs = {}
-        for key, val in obj['attrs'].items():
-            attrs[key] = AttrSchema(**val)
+        attrs = obj.pop('attrs') if 'attrs' in obj else {}
+        attrs = {k: AttrSchema(**v) for k, v in attrs.items()}
         return cls(
             attrs,
-            require_all_keys=obj['require_all_keys'],
-            allow_extra_keys=obj['allow_extra_keys'],
+            require_all_keys=obj.get('require_all_keys'),
+            allow_extra_keys=obj.get('allow_extra_keys'),
         )
 
     def validate(self, attrs: Any) -> None:
diff --git a/xarray_schema/dataarray.py b/xarray_schema/dataarray.py
index 4a71e62..7f3d8d0 100644
--- a/xarray_schema/dataarray.py
+++ b/xarray_schema/dataarray.py
@@ -149,7 +149,7 @@ def attrs(self, value):
         if value is None or isinstance(value, AttrsSchema):
             self._attrs = value
         else:
-            self._attrs = AttrsSchema(value)
+            self._attrs = AttrsSchema(**value)
 
     @property
     def coords(self) -> Optional[CoordsSchema]:
@@ -213,7 +213,7 @@ def validate(self, da: xr.DataArray) -> None:
         if self.chunks is not None:
             self.chunks.validate(da.chunks, da.dims, da.shape)
 
-        if self.attrs:
+        if self.attrs is not None:
             self.attrs.validate(da.attrs)
 
         if self.array_type is not None:
diff --git a/xarray_schema/dataset.py b/xarray_schema/dataset.py
index 9be35ee..8146ef1 100644
--- a/xarray_schema/dataset.py
+++ b/xarray_schema/dataset.py
@@ -47,9 +47,9 @@ def from_json(cls, obj: dict):
                 k: DataArraySchema.from_json(v) for k, v in obj['data_vars'].items()
             }
         if 'coords' in obj:
-            kwargs['coords'] = {k: CoordsSchema.from_json(v) for k, v in obj['coords'].items()}
-        if 'attrs' in obj:
-            kwargs['attrs'] = {k: AttrsSchema.from_json(v) for k, v in obj['attrs'].items()}
+            kwargs['coords'] = CoordsSchema.from_json(obj['coords'])
+        if 'attrs' in obj and obj['attrs'] != {}:
+            kwargs['attrs'] = AttrsSchema.from_json(obj['attrs'])
 
         return cls(**kwargs)
 
@@ -79,10 +79,10 @@ def validate(self, ds: xr.Dataset) -> None:
                     else:
                         da_schema.validate(ds.data_vars[key])
 
-        if self.coords is not None:  # pragma: no cover
-            raise NotImplementedError('coords schema not implemented yet')
+        if self.coords is not None:
+            self.coords.validate(ds.coords)
 
-        if self.attrs:
+        if self.attrs is not None:
             self.attrs.validate(ds.attrs)
 
         if self.checks:
@@ -98,7 +98,7 @@ def attrs(self, value: Union[AttrsSchema, Dict[Hashable, Any], None]):
         if value is None or isinstance(value, AttrsSchema):
             self._attrs = value
         else:
-            self._attrs = AttrsSchema(value)
+            self._attrs = AttrsSchema(**value)
 
     @property
     def data_vars(self) -> Optional[Dict[Hashable, Optional[DataArraySchema]]]: