diff --git a/17-ClassDogs.php b/17-ClassDogs.php
new file mode 100644
index 0000000..2611edb
--- /dev/null
+++ b/17-ClassDogs.php
@@ -0,0 +1,58 @@
+<?php
+
+Class Dogs {
+
+    public string $name = "";
+    public string $breed = "";
+    public int $age = 0;
+    
+    public function __construct ( string $name1, string $breed1, int $age1) {
+    $this -> name = $name1;
+    $this -> breed = $breed1;
+    $this->age = $age1;
+}
+
+public function getDogsData() {
+
+    $data = "
+        <h2> Data Dogs </h2>
+        Name : {$this->name}<br>
+        Breed : {$this ->breed}<br>
+        Age : {$this->age}<br>
+    ";
+    return $data;
+}
+}
+
+/* 3 methods Formats !!!
+
+
+public function setName () {
+    return $this -> name;
+}
+
+public function getName ($name) {
+    $this -> name = $name;
+    return $this -> name;    
+} 
+
+public function setBreed () {
+    return $this -> breed;
+}
+
+public function getBreed ($breed) {
+    $this -> breed = $breed;
+    return $this;
+}
+
+public function setAge () {
+    return $this -> age;
+}
+
+public function getAge ($age) {
+    $this -> age = $age;
+    return $this;
+} */
+
+
+?>
\ No newline at end of file
diff --git a/18-ClassDogs2.php b/18-ClassDogs2.php
new file mode 100644
index 0000000..45b4364
--- /dev/null
+++ b/18-ClassDogs2.php
@@ -0,0 +1,35 @@
+<?php
+
+class Dogs2 extends Dogs {
+
+    public string $type = "";
+
+    public string $firstName = "";
+
+    public function __construct (string $name1, string $firstName, string $breed1, int $age1, string $type1) {
+        $this-> name = $name1;
+        $this -> firstName = $firstName;
+        $this -> breed = $breed1;
+        $this-> age = $age1;
+        $this -> type = $type1;
+    }
+
+    public function __destruct() {
+        echo "This properties get deleted: ".$this-> name;
+    }
+
+    public function getDogsData1() {
+
+        $data1 = "
+            <h2> Data Dogs 2 </h2>
+            Name : {$this->name}<br>
+            First Name : {$this->firstName}<br>
+            Breed : {$this ->breed}<br>
+            Age : {$this->age}<br>
+            Type : {$this->type}<br><br>
+        ";
+        return $data1;
+    }
+}
+
+?>
\ No newline at end of file
diff --git a/19-indexdogs.php b/19-indexdogs.php
new file mode 100644
index 0000000..08671a2
--- /dev/null
+++ b/19-indexdogs.php
@@ -0,0 +1,19 @@
+<?php
+
+require_once("ClassDogs.php");
+
+$dog1 = new Dogs("Max", "Bulldog", 10);
+
+$pet1 = $dog1->getDogsData();
+
+echo $pet1;
+
+require_once("ClassDogs2.php");
+
+$dog2 = new Dogs2( "Maxi", "Max", "Bulldog", 10, "Dog");
+
+$pet2 = $dog2->getDogsData1();
+
+echo $pet2;
+
+?>
\ No newline at end of file
diff --git a/20-ClassAbstract.php b/20-ClassAbstract.php
new file mode 100644
index 0000000..97f74ae
--- /dev/null
+++ b/20-ClassAbstract.php
@@ -0,0 +1,25 @@
+<?php
+
+require_once("ClassInterface.php");
+abstract class Animals {
+
+    public string $name = "";
+    public int $age = 0;
+
+    public function __construct(string $name, int $age) {
+        $this-> name = $name;
+        $this->age = $age;
+    }
+
+    public function getAnimalsData() {
+
+        $data = "
+        <h2>Animals Data</h2>
+        Name : {$this->name}<br>
+        Age : {$this->age}
+    ";
+        return $data;
+}
+}
+
+?>
\ No newline at end of file
diff --git a/21-ClassInterface.php b/21-ClassInterface.php
new file mode 100644
index 0000000..6e944ed
--- /dev/null
+++ b/21-ClassInterface.php
@@ -0,0 +1,12 @@
+<?php
+
+require_once("ClassAbstract.php");
+
+ interface Pets {
+
+    public function getAnimalsData();
+
+}
+
+
+?>
\ No newline at end of file
diff --git a/README.md b/README.md
index e644e6a..07aaab1 100644
--- a/README.md
+++ b/README.md
@@ -134,3 +134,16 @@ Namespaces are qualifiers that solve two different problems:
 2. They allow the same name to be used for more than one class
 
 In this file you will learn how to create and use namespaces.
+
+### [17 - ClassDogs](17-ClassDogs.php) <!-- omit in toc -->
+
+### [18 - ClassDogs2](18-ClassDogs2.php) <!-- omit in toc -->
+
+### [19 - IndexDogs](19-IndexDogs.php) <!-- omit in toc -->
+
+### [20 - Abstract](20-ClassAbstract.php) <!-- omit in toc -->
+
+### [21 - Interface](21-ClassInterface.php) <!-- omit in toc -->
+
+
+These Basics seemed simple but nothing beyond reality, when documenting you see that the methods can be developed in different ways and I commented on one of them because I did not know which one was correct, although the result is the same. For the rest it contains many very interesting sections.
\ No newline at end of file