diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1554,6 +1554,7 @@
     'PhabricatorEdgeGraph' => 'infrastructure/edges/util/PhabricatorEdgeGraph.php',
     'PhabricatorEdgeQuery' => 'infrastructure/edges/query/PhabricatorEdgeQuery.php',
     'PhabricatorEdgeTestCase' => 'infrastructure/edges/__tests__/PhabricatorEdgeTestCase.php',
+    'PhabricatorEdgeType' => 'infrastructure/edges/constants/PhabricatorEdgeType.php',
     'PhabricatorEditor' => 'infrastructure/PhabricatorEditor.php',
     'PhabricatorEmailLoginController' => 'applications/auth/controller/PhabricatorEmailLoginController.php',
     'PhabricatorEmailVerificationController' => 'applications/auth/controller/PhabricatorEmailVerificationController.php',
@@ -1704,6 +1705,7 @@
     'PhabricatorJavelinLinter' => 'infrastructure/lint/linter/PhabricatorJavelinLinter.php',
     'PhabricatorJumpNavHandler' => 'applications/search/engine/PhabricatorJumpNavHandler.php',
     'PhabricatorKeyValueDatabaseCache' => 'applications/cache/PhabricatorKeyValueDatabaseCache.php',
+    'PhabricatorLegacyEdgeType' => 'infrastructure/edges/constants/PhabricatorLegacyEdgeType.php',
     'PhabricatorLegalpadConfigOptions' => 'applications/legalpad/config/PhabricatorLegalpadConfigOptions.php',
     'PhabricatorLegalpadPHIDTypeDocument' => 'applications/legalpad/phid/PhabricatorLegalpadPHIDTypeDocument.php',
     'PhabricatorLipsumArtist' => 'applications/lipsum/image/PhabricatorLipsumArtist.php',
@@ -4393,6 +4395,7 @@
     'PhabricatorEdgeGraph' => 'AbstractDirectedGraph',
     'PhabricatorEdgeQuery' => 'PhabricatorQuery',
     'PhabricatorEdgeTestCase' => 'PhabricatorTestCase',
+    'PhabricatorEdgeType' => 'Phobject',
     'PhabricatorEditor' => 'Phobject',
     'PhabricatorEmailLoginController' => 'PhabricatorAuthController',
     'PhabricatorEmailVerificationController' => 'PhabricatorAuthController',
@@ -4550,6 +4553,7 @@
     'PhabricatorIteratedMD5PasswordHasher' => 'PhabricatorPasswordHasher',
     'PhabricatorJavelinLinter' => 'ArcanistLinter',
     'PhabricatorKeyValueDatabaseCache' => 'PhutilKeyValueCache',
+    'PhabricatorLegacyEdgeType' => 'PhabricatorEdgeType',
     'PhabricatorLegalpadConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorLegalpadPHIDTypeDocument' => 'PhabricatorPHIDType',
     'PhabricatorLipsumGenerateWorkflow' => 'PhabricatorLipsumManagementWorkflow',
diff --git a/src/infrastructure/edges/constants/PhabricatorEdgeConfig.php b/src/infrastructure/edges/constants/PhabricatorEdgeConfig.php
--- a/src/infrastructure/edges/constants/PhabricatorEdgeConfig.php
+++ b/src/infrastructure/edges/constants/PhabricatorEdgeConfig.php
@@ -78,6 +78,13 @@
   const TYPE_OBJECT_NEEDS_SIGNATURE     = 49;
   const TYPE_SIGNATURE_NEEDED_BY_OBJECT = 50;
 
+/* !!! STOP !!! STOP !!! STOP !!! STOP !!! STOP !!! STOP !!! STOP !!! STOP !! */
+
+  // HEY! DO NOT ADD NEW CONSTANTS HERE!
+  // Instead, subclass PhabricatorEdgeType.
+
+/* !!! STOP !!! STOP !!! STOP !!! STOP !!! STOP !!! STOP !!! STOP !!! STOP !! */
+
   const TYPE_TEST_NO_CYCLE              = 9000;
 
   const TYPE_PHOB_HAS_ASANATASK         = 80001;
@@ -89,6 +96,34 @@
   const TYPE_PHOB_HAS_JIRAISSUE         = 80004;
   const TYPE_JIRAISSUE_HAS_PHOB         = 80005;
 
+  public static function getLegacyTypes($exclude) {
+    $consts = array_merge(
+      range(1, 50),
+      array(9000),
+      range(80000, 80005));
+    $consts = array_diff($consts, $exclude);
+
+    $map = array();
+    foreach ($consts as $const) {
+      $prevent_cycles = self::shouldPreventCycles($const);
+      $inverse_constant = self::getInverse($const);
+
+      $map[$const] = id(new PhabricatorLegacyEdgeType())
+        ->setEdgeConstant($const)
+        ->setShouldPreventCycles($prevent_cycles)
+        ->setInverseEdgeConstant($inverse_constant)
+        ->setStrings(
+          array(
+            self::getAddStringForEdgeType($const),
+            self::getRemoveStringForEdgeType($const),
+            self::getEditStringForEdgeType($const),
+            self::getFeedStringForEdgeType($const),
+          ));
+    }
+
+    return $map;
+  }
+
   public static function getInverse($edge_type) {
     static $map = array(
       self::TYPE_TASK_HAS_COMMIT => self::TYPE_COMMIT_HAS_TASK,
@@ -136,7 +171,7 @@
       self::TYPE_DREV_HAS_COMMIT => self::TYPE_COMMIT_HAS_DREV,
       self::TYPE_COMMIT_HAS_DREV => self::TYPE_DREV_HAS_COMMIT,
 
-      self::TYPE_OBJECT_HAS_CONTRIBUTOR => self::TYPE_SUBSCRIBED_TO_OBJECT,
+      self::TYPE_OBJECT_HAS_CONTRIBUTOR => self::TYPE_CONTRIBUTED_TO_OBJECT,
       self::TYPE_CONTRIBUTED_TO_OBJECT => self::TYPE_OBJECT_HAS_CONTRIBUTOR,
 
       self::TYPE_TASK_HAS_MOCK => self::TYPE_MOCK_HAS_TASK,
diff --git a/src/infrastructure/edges/constants/PhabricatorEdgeType.php b/src/infrastructure/edges/constants/PhabricatorEdgeType.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/edges/constants/PhabricatorEdgeType.php
@@ -0,0 +1,217 @@
+<?php
+
+/**
+ * Defines an edge type.
+ *
+ * Edges are typed, directed connections between two objects. They are used to
+ * represent most simple relationships, like when a user is subscribed to an
+ * object or an object is a member of a project.
+ *
+ * @task load   Loading Types
+ */
+abstract class PhabricatorEdgeType extends Phobject {
+
+  abstract public function getEdgeConstant();
+
+  public function getInverseEdgeConstant() {
+    return null;
+  }
+
+  public function shouldPreventCycles() {
+    return false;
+  }
+
+  public function getTransactionAddString(
+    $actor,
+    $add_count,
+    $add_edges) {
+
+    return pht(
+      '%s added %s edge(s): %s.',
+      $actor,
+      $add_count,
+      $add_edges);
+  }
+
+  public function getTransactionRemoveString(
+    $actor,
+    $rem_count,
+    $rem_edges) {
+
+    return pht(
+      '%s removed %s edge(s): %s.',
+      $actor,
+      $rem_count,
+      $rem_edges);
+  }
+
+  public function getTransactionEditString(
+    $actor,
+    $total_count,
+    $add_count,
+    $add_edges,
+    $rem_count,
+    $rem_edges) {
+
+    return pht(
+      '%s edited %s edges, added %s: %s; removed %s: %s.',
+      $actor,
+      $total_count,
+      $add_count,
+      $add_edges,
+      $rem_count,
+      $rem_edges);
+  }
+
+  public function getFeedAddString(
+    $actor,
+    $object,
+    $add_count,
+    $add_edges) {
+
+    return pht(
+      '%s added %s edge(s) to %s: %s.',
+      $actor,
+      $add_count,
+      $object,
+      $add_edges);
+  }
+
+  public function getFeedRemoveString(
+    $actor,
+    $object,
+    $rem_count,
+    $rem_edges) {
+
+    return pht(
+      '%s removed %s edge(s) from %s: %s.',
+      $actor,
+      $object,
+      $rem_count,
+      $rem_edges);
+  }
+
+  public function getFeedEditString(
+    $actor,
+    $object,
+    $total_count,
+    $add_count,
+    $add_edges,
+    $rem_count,
+    $rem_edges) {
+
+    return pht(
+      '%s edited %s edges for %s, added %s: %s; removed %s: %s.',
+      $actor,
+      $total_count,
+      $object,
+      $add_count,
+      $add_edges,
+      $rem_count,
+      $rem_edges);
+  }
+
+
+/* -(  Loading Types  )------------------------------------------------------ */
+
+
+  /**
+   * @task load
+   */
+  public static function getAllTypes() {
+    static $type_map;
+
+    if ($type_map === null) {
+      $types = id(new PhutilSymbolLoader())
+        ->setAncestorClass(__CLASS__)
+        ->loadObjects();
+
+      $map = array();
+
+
+      // TODO: Remove this once everything is migrated.
+      $exclude = mpull($types, 'getEdgeConstant');
+      $map = PhabricatorEdgeConfig::getLegacyTypes($exclude);
+      unset($types['PhabricatorLegacyEdgeType']);
+
+
+      foreach ($types as $class => $type) {
+        $const = $type->getEdgeConstant();
+
+        if (!is_int($const) || ($const <= 0)) {
+          throw new Exception(
+            pht(
+              'Edge type "%s" has an invalid edge constant. Edge constants '.
+              'must be positive integers.',
+              $class));
+        }
+
+        if (isset($map[$const])) {
+          throw new Exception(
+            pht(
+              'Two edge types ("%s", "%s") share the same edge constant '.
+              '(%d). Each edge type must have a unique constant.',
+              $class,
+              get_class($map[$const]),
+              $const));
+        }
+
+        $map[$const] = $type;
+      }
+
+      // Check that all the inverse edge definitions actually make sense. If
+      // edge type A says B is its inverse, B must exist and say that A is its
+      // inverse.
+
+      foreach ($map as $const => $type) {
+        $inverse = $type->getInverseEdgeConstant();
+        if ($inverse === null) {
+          continue;
+        }
+
+        if (empty($map[$inverse])) {
+          throw new Exception(
+            pht(
+              'Edge type "%s" ("%d") defines an inverse type ("%d") which '.
+              'does not exist.',
+              get_class($type),
+              $const,
+              $inverse));
+        }
+
+        $inverse_inverse = $map[$inverse]->getInverseEdgeConstant();
+        if ($inverse_inverse !== $const) {
+          throw new Exception(
+            pht(
+              'Edge type "%s" ("%d") defines an inverse type ("%d"), but that '.
+              'inverse type defines a different type ("%d") as its '.
+              'inverse.',
+              get_class($type),
+              $const,
+              $inverse,
+              $inverse_inverse));
+        }
+      }
+
+      $type_map = $map;
+    }
+
+    return $type_map;
+  }
+
+
+  /**
+   * @task load
+   */
+  public static function getByConst($const) {
+    $type = idx(self::getAllTypes(), $const);
+
+    if (!$type) {
+      throw new Exception(
+        pht('Unknown edge constant "%s"!', $const));
+    }
+
+    return $type;
+  }
+
+}
diff --git a/src/infrastructure/edges/constants/PhabricatorLegacyEdgeType.php b/src/infrastructure/edges/constants/PhabricatorLegacyEdgeType.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/edges/constants/PhabricatorLegacyEdgeType.php
@@ -0,0 +1,119 @@
+<?php
+
+/**
+ * Supports legacy edges. Do not use or extend this class!
+ *
+ * TODO: Move all edge constants out of PhabricatorEdgeConfig, then throw this
+ * away.
+ */
+final class PhabricatorLegacyEdgeType extends PhabricatorEdgeType {
+
+  private $edgeConstant;
+  private $inverseEdgeConstant;
+  private $shouldPreventCycles;
+  private $strings;
+
+  public function getEdgeConstant() {
+    return $this->edgeConstant;
+  }
+
+  public function getInverseEdgeConstant() {
+    return $this->inverseEdgeConstant;
+  }
+
+  public function getShouldPreventCycles() {
+    return $this->shouldPreventCycles;
+  }
+
+  public function setEdgeConstant($edge_constant) {
+    $this->edgeConstant = $edge_constant;
+    return $this;
+  }
+
+  public function setInverseEdgeConstant($inverse_edge_constant) {
+    $this->inverseEdgeConstant = $inverse_edge_constant;
+    return $this;
+  }
+
+  public function setShouldPreventCycles($should_prevent_cycles) {
+    $this->shouldPreventCycles = $should_prevent_cycles;
+    return $this;
+  }
+
+  public function setStrings(array $strings) {
+    $this->strings = $strings;
+    return $this;
+  }
+
+  private function getString($idx, array $argv) {
+    array_unshift($argv, idx($this->strings, $idx, ''));
+
+    // TODO: Burn this class in a fire. Just hiding this from lint for now.
+    $pht_func = 'pht';
+    return call_user_func_array($pht_func, $argv);
+  }
+
+  public function getTransactionAddString(
+    $actor,
+    $add_count,
+    $add_edges) {
+
+    $args = func_get_args();
+    return $this->getString(0, $args);
+  }
+
+  public function getTransactionRemoveString(
+    $actor,
+    $rem_count,
+    $rem_edges) {
+
+    $args = func_get_args();
+    return $this->getString(1, $args);
+  }
+
+  public function getTransactionEditString(
+    $actor,
+    $total_count,
+    $add_count,
+    $add_edges,
+    $rem_count,
+    $rem_edges) {
+
+    $args = func_get_args();
+    return $this->getString(2, $args);
+  }
+
+  public function getFeedAddString(
+    $actor,
+    $object,
+    $add_count,
+    $add_edges) {
+
+    $args = func_get_args();
+    return $this->getString(3, $args);
+  }
+
+  public function getFeedRemoveString(
+    $actor,
+    $object,
+    $rem_count,
+    $rem_edges) {
+
+    $args = func_get_args();
+    return $this->getString(3, $args);
+  }
+
+  public function getFeedEditString(
+    $actor,
+    $object,
+    $total_count,
+    $add_count,
+    $add_edges,
+    $rem_count,
+    $rem_edges) {
+
+    $args = func_get_args();
+    return $this->getString(3, $args);
+  }
+
+}