Created using Colaboratory

tutorial/Logica_tutorial.ipynb

@@ -124,7 +124,7 @@
         "#@title Install Logica.\n",
         "!pip install logica"
       ],
-      "execution_count": 9,
+      "execution_count": null,
       "outputs": [
         {
           "output_type": "stream",
@@ -149,7 +149,7 @@
         "# auth.authenticate_user()\n",
         "# colab_logica.SetProject('YOUR_PROJECT')"
       ],
-      "execution_count": 10,
+      "execution_count": null,
       "outputs": []
     },
     {
@@ -8938,7 +8938,7 @@
         "  w == a.z.w;\n",
         "  "
       ],
-      "execution_count": 12,
+      "execution_count": null,
       "outputs": [
         {
           "output_type": "display_data",
@@ -49117,6 +49117,43 @@
           "metadata": {}
         }
       ]
+    },
+    {
+      "cell_type": "markdown",
+      "source": [
+        "### Injectible and Concrete predicates\n",
+        "\n",
+        "A predicate denoted with `distinct` keyword is called _aggregating_. Note that `distinct` can be implict if aggregated value.\n",
+        "\n",
+        "```\n",
+        "# Example 1 of aggregating predicate.\n",
+        "\n",
+        "EmployeesOfRole(role:, employees? Array= office -> name) distinct :-\n",
+        "  Employee(name:, role:, office:)\n",
+        "\n",
+        "# Example 2 of aggregating predicate.\n",
+        "\n",
+        "EmployeesOfRoleF(role:) Array= office -> name :-\n",
+        "  Employee(name:, role:, office:)\n",
+        "```\n",
+        "\n",
+        "A predicate in Logica is called _injectable_ if it is defined by a single, non-aggregating rule. Injectable predicates may contain aggregating expressions. \n",
+        "\n",
+        "A predicate is called _concrete_ if it can be computed as a table, i.e. itself compiled as a SQL query.\n",
+        "\n",
+        "Any predicate in Logica must be _injectible_ or _concrete_ or both.\n",
+        "\n",
+        "Only _concrete_ predicates can be compiled to SQL. When a predicate Q is compiled and it uses a sub-predicate P then:\n",
+        "\n",
+        "* if P is injectible, then it's substituted into the formula of Q,\n",
+        "\n",
+        "* otherwise P must be concrete, and it is compiled as a sub-query.\n",
+        "\n",
+        "Aggregating expressions are always compiled into sub-queries."
+      ],
+      "metadata": {
+        "id": "q55qN2URLwu-"
+      }
     }
   ]
 }