diff --git a/src/controller.jsonnet b/src/controller.jsonnet
new file mode 100644
index 0000000..578138d
--- /dev/null
+++ b/src/controller.jsonnet
@@ -0,0 +1,42 @@
+local entity = import '../lib/entity.libsonnet';
+
+entity
+{
+  '$id': 'https://picc.app/schemata/v0.1-dev/controller',
+  title: 'Controller',
+  description: 'Describes a relationship between two entities.',
+
+  properties+: {
+    module: {
+      type: 'string',
+      description: 'Module name of the controller.',
+    },
+    arg: {
+      description: 'Additional arguments. Can be any JSON type.',
+    },
+    entities: {
+      type: 'array',
+      description: 'Entities this controller controls.',
+      items:
+        $.properties.id,
+    },
+    measures: {
+      type: 'array',
+      description: 'List of variables this controller measures.',
+      items: 'string',
+      minItems: 1,
+      uniqueItems: true,
+    },
+    controls: {
+      type: 'array',
+      description: 'List of variables this controller controls.',
+      items: 'string',
+      minItems: 1,
+      uniqueItems: true,
+    }
+  },
+  required+: [
+    'module',
+    'entities',
+  ],
+}
diff --git a/src/devices/sensor.jsonnet b/src/devices/sensor.jsonnet
index 7b6ecbb..5e4c519 100644
--- a/src/devices/sensor.jsonnet
+++ b/src/devices/sensor.jsonnet
@@ -1,3 +1,4 @@
+local types = import 'types.libsonnet';
 local entity = import 'entity.libsonnet';
 
 entity
@@ -7,4 +8,13 @@ entity
   description: |||
     A sensor device entity.
   |||,
+
+  properties+: {
+    measures: {
+      type: 'array',
+      items: types.id,
+      description: 'List of variables measured by sensor.',
+      uniqueItems: true,
+    }
+  }
 }
diff --git a/src/docs.jsonnet b/src/docs.jsonnet
index f9fa1d5..69fd7ee 100644
--- a/src/docs.jsonnet
+++ b/src/docs.jsonnet
@@ -1,7 +1,7 @@
 local loom = import 'lib/loom.libsonnet';
 
 loom.weave(import 'src/entity.jsonnet') +
-loom.weave(import 'src/room.jsonnet') +
+loom.weave(import 'src/locations/room.jsonnet') +
 loom.weave(import 'src/relationship.jsonnet') +
 loom.weave(import 'src/devices/light.jsonnet') +
 loom.weave(import 'src/devices/sensor.jsonnet')
diff --git a/src/locations/building.jsonnet b/src/locations/building.jsonnet
index c313703..71afeba 100644
--- a/src/locations/building.jsonnet
+++ b/src/locations/building.jsonnet
@@ -9,6 +9,7 @@ entity
   |||,
 
   properties+: {
+    location: types.location,
     rooms: {
       type: 'array',
       description: 'Rooms contained in this building.',
@@ -21,17 +22,5 @@ entity
         ],
       },
     },
-    relationships: {
-      type: 'array',
-      description: 'Relationships that bind other entities to this room.',
-      items: {
-        oneOf: [
-          {
-            '$ref': 'https://picc.app/schemata/v0.1-dev/relationship',
-          },
-          $.properties.id,
-        ],
-      },
-    },
   },
 }
diff --git a/src/locations/room.jsonnet b/src/locations/room.jsonnet
index cd2fa3e..9f24718 100644
--- a/src/locations/room.jsonnet
+++ b/src/locations/room.jsonnet
@@ -1,4 +1,5 @@
-local entity = import '../lib/entity.libsonnet';
+local entity = import 'entity.libsonnet';
+local types = import 'types.libsonnet';
 
 entity
 {
@@ -9,6 +10,7 @@ entity
   |||,
 
   properties+: {
+    location: types.location,
     relationships: {
       type: 'array',
       description: 'Relationships that bind other entities to this room.',
diff --git a/src/relationship.jsonnet b/src/relationship.jsonnet
index 91635aa..6197efc 100644
--- a/src/relationship.jsonnet
+++ b/src/relationship.jsonnet
@@ -4,26 +4,16 @@ entity
 {
   '$id': 'https://picc.app/schemata/v0.1-dev/relationship',
   title: 'Relationship',
-  description: 'Describes a relationship between two entities.',
+  description: 'Describes a relationship between entities. An arity of 1 is used to describe a property of an entity (a relationship of the entity to itself).',
 
   properties+: {
-    module: {
-      type: 'string',
-      description: 'Module name of the relationship.',
-    },
-    entities: {
-      type: 'array',
-      description: 'Entities invloved in the relationship.',
-      items:
-        $.properties.id,
-
-    },
-    arg: {
-      description: 'Additional arguments. Can be any JSON type.',
+    arity: {
+      type: 'number',
+      description: 'The number of entities involved in the relationship.',
+      minimum: 1,
     },
   },
   required+: [
-    'module',
-    'entities',
+    'description',
   ],
 }
diff --git a/src/schemata.jsonnet b/src/schemata.jsonnet
index 43c4515..e7e4c64 100644
--- a/src/schemata.jsonnet
+++ b/src/schemata.jsonnet
@@ -1,11 +1,14 @@
 local loom = import 'lib/loom.libsonnet';
 
 loom.tangle(import 'src/entity.jsonnet') +
+loom.tangle(import 'src/relationship.jsonnet') +
+loom.tangle(import 'src/controller.jsonnet') +
+
+loom.tangle(import 'src/variables/real.jsonnet') +
 
 loom.tangle(import 'src/locations/room.jsonnet') +
 loom.tangle(import 'src/locations/building.jsonnet') +
 loom.tangle(import 'src/locations/site.jsonnet') +
 
-loom.tangle(import 'src/relationship.jsonnet') +
 loom.tangle(import 'src/devices/light.jsonnet') +
 loom.tangle(import 'src/devices/sensor.jsonnet')
diff --git a/src/variables/real.jsonnet b/src/variables/real.jsonnet
new file mode 100644
index 0000000..fafe758
--- /dev/null
+++ b/src/variables/real.jsonnet
@@ -0,0 +1,34 @@
+local entity = import '../lib/entity.libsonnet';
+
+entity
+{
+  '$id': 'https://picc.app/schemata/v0.1-dev/variables/real',
+  title: 'Real',
+  description: 'Real-valued variable.',
+
+  properties+: {
+    moreThan: {
+        type: 'number',
+        description: 'Open lower bound on value of variable.',
+    },
+    moreThanEq : {
+        type: 'number',
+        description: 'Closed lower bound on value of variable.',
+    },
+    lessThan: {
+        type: 'number',
+        description: 'Open upper bound on value of variable.',
+    },
+    lessThanEq: {
+        type: 'number',
+        description: 'Closed lower bound on the value of variable.',
+    },
+    distribution: {
+        type: 'string',
+        description: 'Assumed distribution of variable.',
+        enum: ['normal', 'uniform', 'exponential', 'gamma'],
+    },
+  },
+  required+: [
+  ],
+}