diff --git a/UPGRADE.md b/UPGRADE.md
index 3e65299cfd6..10becb94a6d 100644
--- a/UPGRADE.md
+++ b/UPGRADE.md
@@ -8,6 +8,30 @@ awareness about deprecated code.
 
 # Upgrade to 3.2
 
+## Deprecated `udf*` methods of the `SQLitePlatform` methods.
+
+The following `SQLServerPlatform` methods have been deprecated in favor of their implementations
+in the `UserDefinedFunctions` class:
+- `udfSqrt()`,
+- `udfMod()`,
+- `udfLocate()`.
+
+## `SQLServerPlatform` methods marked internal.
+
+The following `SQLServerPlatform` methods have been marked internal:
+- `getDefaultConstraintDeclarationSQL()`,
+- `getAddExtendedPropertySQL()`,
+- `getDropExtendedPropertySQL()`,
+- `getUpdateExtendedPropertySQL()`.
+
+## `OraclePlatform` methods marked internal.
+
+The `OraclePlatform::getCreateAutoincrementSql()` and `::getDropAutoincrementSql()` have been marked internal.
+
+## Deprecated `OraclePlatform::assertValidIdentifier()`
+
+The `OraclePlatform::assertValidIdentifier()` method has been deprecated.
+
 ## Deprecated features of `Table::getColumns()`
 
 1. Using the returned array keys as column names is deprecated. Retrieve the name from the column
diff --git a/psalm.xml.dist b/psalm.xml.dist
index 1775c8e02a6..a0099aad042 100644
--- a/psalm.xml.dist
+++ b/psalm.xml.dist
@@ -150,6 +150,10 @@
                     TODO: remove in 4.0.0
                 -->
                 <referencedMethod name="Doctrine\DBAL\Schema\Schema::getMigrateToSql"/>
+                <!--
+                    TODO: remove in 4.0.0
+                -->
+                <referencedMethod name="Doctrine\DBAL\Platforms\OraclePlatform::assertValidIdentifier"/>
             </errorLevel>
         </DeprecatedMethod>
         <DeprecatedProperty>
diff --git a/src/Driver/API/SQLite/UserDefinedFunctions.php b/src/Driver/API/SQLite/UserDefinedFunctions.php
new file mode 100644
index 00000000000..6bce02291e0
--- /dev/null
+++ b/src/Driver/API/SQLite/UserDefinedFunctions.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace Doctrine\DBAL\Driver\API\SQLite;
+
+use function strpos;
+
+/**
+ * User-defined SQLite functions.
+ *
+ * @internal
+ */
+final class UserDefinedFunctions
+{
+    /**
+     * User-defined function that implements MOD().
+     *
+     * @param int $a
+     * @param int $b
+     *
+     * @return int
+     */
+    public static function mod($a, $b)
+    {
+        return $a % $b;
+    }
+
+    /**
+     * User-defined function that implements LOCATE().
+     *
+     * @param string $str
+     * @param string $substr
+     * @param int    $offset
+     *
+     * @return int
+     */
+    public static function locate($str, $substr, $offset = 0)
+    {
+        // SQL's LOCATE function works on 1-based positions, while PHP's strpos works on 0-based positions.
+        // So we have to make them compatible if an offset is given.
+        if ($offset > 0) {
+            $offset -= 1;
+        }
+
+        $pos = strpos($str, $substr, $offset);
+
+        if ($pos !== false) {
+            return $pos + 1;
+        }
+
+        return 0;
+    }
+}
diff --git a/src/Platforms/OraclePlatform.php b/src/Platforms/OraclePlatform.php
index a5a01cb963b..7a0d82e0b2f 100644
--- a/src/Platforms/OraclePlatform.php
+++ b/src/Platforms/OraclePlatform.php
@@ -35,6 +35,8 @@ class OraclePlatform extends AbstractPlatform
     /**
      * Assertion for Oracle identifiers.
      *
+     * @deprecated
+     *
      * @link http://docs.oracle.com/cd/B19306_01/server.102/b14200/sql_elements008.htm
      *
      * @param string $identifier
@@ -490,6 +492,8 @@ public function getDropViewSQL($name)
     }
 
     /**
+     * @internal The method should be only used from within the OraclePlatform class hierarchy.
+     *
      * @param string $name
      * @param string $table
      * @param int    $start
@@ -557,6 +561,8 @@ public function getCreateAutoincrementSql($name, $table, $start = 1)
     }
 
     /**
+     * @internal The method should be only used from within the OracleSchemaManager class hierarchy.
+     *
      * Returns the SQL statements to drop the autoincrement for the given table name.
      *
      * @param string $table The table name to drop the autoincrement for.
diff --git a/src/Platforms/SQLServerPlatform.php b/src/Platforms/SQLServerPlatform.php
index b9e862851b3..3c61cce87d2 100644
--- a/src/Platforms/SQLServerPlatform.php
+++ b/src/Platforms/SQLServerPlatform.php
@@ -438,6 +438,8 @@ protected function getCreateColumnCommentSQL($tableName, $columnName, $comment)
     /**
      * Returns the SQL snippet for declaring a default constraint.
      *
+     * @internal The method should be only used from within the SQLServerPlatform class hierarchy.
+     *
      * @param string  $table  Name of the table to return the default constraint declaration for.
      * @param mixed[] $column Column definition.
      *
@@ -843,6 +845,8 @@ protected function getRenameIndexSQL($oldIndexName, Index $index, $tableName)
     /**
      * Returns the SQL statement for adding an extended property to a database object.
      *
+     * @internal The method should be only used from within the SQLServerPlatform class hierarchy.
+     *
      * @link http://msdn.microsoft.com/en-us/library/ms180047%28v=sql.90%29.aspx
      *
      * @param string      $name       The name of the property to add.
@@ -876,6 +880,8 @@ public function getAddExtendedPropertySQL(
     /**
      * Returns the SQL statement for dropping an extended property from a database object.
      *
+     * @internal The method should be only used from within the SQLServerPlatform class hierarchy.
+     *
      * @link http://technet.microsoft.com/en-gb/library/ms178595%28v=sql.90%29.aspx
      *
      * @param string      $name       The name of the property to drop.
@@ -907,6 +913,8 @@ public function getDropExtendedPropertySQL(
     /**
      * Returns the SQL statement for updating an extended property of a database object.
      *
+     * @internal The method should be only used from within the SQLServerPlatform class hierarchy.
+     *
      * @link http://msdn.microsoft.com/en-us/library/ms186885%28v=sql.90%29.aspx
      *
      * @param string      $name       The name of the property to update.
diff --git a/src/Platforms/SqlitePlatform.php b/src/Platforms/SqlitePlatform.php
index 7f6e6c1619c..07dad0cca65 100644
--- a/src/Platforms/SqlitePlatform.php
+++ b/src/Platforms/SqlitePlatform.php
@@ -2,6 +2,7 @@
 
 namespace Doctrine\DBAL\Platforms;
 
+use Doctrine\DBAL\Driver\API\SQLite\UserDefinedFunctions;
 use Doctrine\DBAL\Exception;
 use Doctrine\DBAL\Schema\Column;
 use Doctrine\DBAL\Schema\Constraint;
@@ -27,7 +28,6 @@
 use function sqrt;
 use function str_replace;
 use function strlen;
-use function strpos;
 use function strtolower;
 use function trim;
 
@@ -594,6 +594,8 @@ public function getTruncateTableSQL($tableName, $cascade = false)
     /**
      * User-defined function for Sqlite that is used with PDO::sqliteCreateFunction().
      *
+     * @deprecated The driver will use {@link sqrt()} in the next major release.
+     *
      * @param int|float $value
      *
      * @return float
@@ -606,6 +608,8 @@ public static function udfSqrt($value)
     /**
      * User-defined function for Sqlite that implements MOD(a, b).
      *
+     * @deprecated The driver will use {@link UserDefinedFunctions::mod()} in the next major release.
+     *
      * @param int $a
      * @param int $b
      *
@@ -613,10 +617,12 @@ public static function udfSqrt($value)
      */
     public static function udfMod($a, $b)
     {
-        return $a % $b;
+        return UserDefinedFunctions::mod($a, $b);
     }
 
     /**
+     * @deprecated The driver will use {@link UserDefinedFunctions::locate()} in the next major release.
+     *
      * @param string $str
      * @param string $substr
      * @param int    $offset
@@ -625,19 +631,7 @@ public static function udfMod($a, $b)
      */
     public static function udfLocate($str, $substr, $offset = 0)
     {
-        // SQL's LOCATE function works on 1-based positions, while PHP's strpos works on 0-based positions.
-        // So we have to make them compatible if an offset is given.
-        if ($offset > 0) {
-            $offset -= 1;
-        }
-
-        $pos = strpos($str, $substr, $offset);
-
-        if ($pos !== false) {
-            return $pos + 1;
-        }
-
-        return 0;
+        return UserDefinedFunctions::locate($str, $substr, $offset);
     }
 
     /**