diff --git a/src/Currency.php b/src/Currency.php
index bedadd7..02cf51f 100644
--- a/src/Currency.php
+++ b/src/Currency.php
@@ -31,6 +31,13 @@ class Currency extends Model {
     }
     return $this->latest;
   }
+  protected $sources;
+  public function sources(): ?array {
+    if ($this->sources === null) {
+      $this->sources = $this->parentOf(Source::class, [Model::CHILD_KEY => 'currency_id']);
+    }
+    return $this->sources;
+  }
 
   protected static $fields = ['code', 'name'];
   public static function add(ModelFactory $factory, $info) {
@@ -49,7 +56,7 @@ class Currency extends Model {
   protected function checkCode(string $code): bool {
     return ($this->find(Currency::class)->where([['code', $code]])->one()) ? true : false;
   }
-  public function edit($info) {
+  public function edit($info): bool {
     $data = array_intersect_key((array) $info, array_combine(self::$fields, self::$fields));
     $edited = false;
     foreach ($data as $field => $value) {
diff --git a/src/Source.php b/src/Source.php
new file mode 100644
index 0000000..a271cb2
--- /dev/null
+++ b/src/Source.php
@@ -0,0 +1,27 @@
+<?php
+namespace ProVM\Money;
+
+use Carbon\CarbonInterval;
+use ProVM\Common\Alias\Model;
+
+/**
+ * @property int $id
+ * @property Currency $currency_id
+ * @property string $url
+ * @property \DateInterval $frecuency
+ */
+class Source extends Model {
+  protected $currency;
+  public function currency(): ?Currency {
+    if ($this->currency === null) {
+      $this->currency = $this->childOf(Currency::class, [Model::SELF_KEY => 'currency_id']);
+    }
+    return $this->currency;
+  }
+  public function frecuency(\DateInterval $frecuency = null) {
+    if ($frecuency == null) {
+      return new \CarbonInterval($this->fecuency);
+    }
+    $this->frecuency = CarbonInterval::getDateIntervalSpec($frecuency);
+  }
+}
diff --git a/src/Value.php b/src/Value.php
index 66824aa..4c51532 100644
--- a/src/Value.php
+++ b/src/Value.php
@@ -46,7 +46,7 @@ class Value extends Model {
     $result->value = $value->asArray();
     return $result;
   }
-  public function edit($info) {
+  public function edit($info): bool {
     $data = array_intersect_key((array) $info, array_combine(self::$fields, self::$fields));
     $edited = false;
     foreach ($data as $field => $value) {