1. Node provides a template that all derived classes must adhere to. By defining required attributes and methods in the Node abstract base class, it ensures any derived classes will have the necessary functionality to be used as a node in the file tree. However, concrete methods in the derived classes can be varied as per the unique requirement of these classes, provided they do not violate the structure outlined by Node.

2. The parent-child relationship between nodes is typically maintained through references. Each Node has a parent attribute which holds a reference to its parent node. When a Node is created, it is assigned a parent, and it may also add itself to the parent’s list of children (if such functionality is implemented in the child class). This creates a two-way link between the parent and child nodes. When a Node is deleted, these links are typically also removed to ensure the integrity of the tree.

   However, as the Node class is an abstract base class, it does not directly handle these relationships - this would be the responsibility of the concrete classes that inherit from Node, such as Directory or File.