Update object-inheritance.md

articles/modeling/object-inheritance.md

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+# Object Inheritance 
+
+## What 
+- A **model** contains common resuable information that can be referenced in your endpoint definitions or other models in your API design. 
+- When a model derives its properties from another model, the event is called **inheritance**. 
+- The model which contains the common set of properties and fields becomes a parent to other models, and it is called the **base type**.
+- The model which inherits the common set of properties and fields is known as the **derived type**.
+- If a base type inherits its properties from another model, the derived type automatically inherits the same properties indicating that inheritance is **transitive**. 
+- OpenAPI Specification v2 uses the **allOf** syntax to declare inheritance. 
+- **allOf** obtains a collection of object definitions validated independently but, collectively make up a single object. 
+
+## Why 
+- Inheritance makes your API design more compact. It helps avoid duplication of common properties and fields. 
+
+## Best Practices 
+
+<!-- theme: info --> 
+> Avoid using contradictory declarations such as declaring properties with the samer name but dissimilar data type in your base model and derived model. 
+
+### Example 
+
+```
+{
+  Vehicle: 
+    type: object
+    properties: 
+      brand: 
+        type: string 
+  Sedan: 
+    allOf: # (This keyword combines the Vehicle model and the Sedan model) 
+      $ref: '#/definitions/Vehicle'
+      type: object
+      properties: 
+        isNew:
+          type: boolean
+}
+```