Many of the terms used in trees relate to terms used in family trees. Having this in mind can help us to better understand some of the terminology involved with abstract trees. Here we have a sample family tree.

• Ancestor - The ancestors of a node are those reached from child to parent relationships. We can think of this as our parents and our parent’s parents, and so on.
  • Let’s look at all of the ancestors of each of our nodes in the family tree.
    • Ava’s ancestors: Uzzi, Joe, Myra. This is because, Uzzi is the parent of Ava, Joe is the parent of Uzzi, and Myra is the parent of Joe. Try to work out the following and click the name to reveal the ancestors.
      Uma:

      Zia, Myra - Zia is the parent of Uma and Myra is the parent of Zia.
      Myra:

      None - Myra does not have a parent node.
      Raju:

      Myra - Myra is the parent of Raju.
      Bev:

      Uzzi, Joe, Myra - Uzzi is the parent of Bev, Joe is the parent of Uzzi, and Myra is the parent of Joe.
• Descendant - The descendants of a node are those reached from parent to child relationships. We can think of this as our children and our children’s children and so on.
  • Let’s look at all of the descendants of each of our nodes in the family tree.
    • Ava’s descendants: None. Ava has no child nodes and thus, no descendants. Try to work out the following and click the name to reveal the descendants.
      Uma:

      Ang - Ang is the child of Uma
      Myra:

      Raju, Joe, Zia, Uzzi, Bert, Uma, Bev, Ava, Ang, Isla, Eoin - All of the nodes in a tree will be descendants of the root. To work it out: Raju, Joe and Zia are the children of Myra, Uma is the child of Zia, Ang is the child of Uma, and we can work the rest out for Joe’s children.
      Raju:

      None - Raju has no child nodes.
      Bev:

      Isla, Eoin - Isla is the child of Bev and Eoin is the child of Isla.
• Siblings - Nodes which share the same parent
  • We can think about the siblings of all of our nodes in the family tree.
    • Ava’s siblings: Bev - Uzzi is the parent node of Ava; Uzzi has two child nodes, Ava and Bev. Try to work out the following and click the name to reveal the siblings.
      Uma:

      None - Zia is the parent node of Uma; Zia has only one child node, Uma.
      Myra:

      None - Myra is the root and thus does not have a parent node resulting in no siblings.
      Raju:

      Joe, Zia - Myra is the parent node of Raju; Myra has three child nodes, Joe, Zia, and Raju
      Bev:

      Ava - Uzzi is the parent node of Bev; Uzzi has two child nodes, Bev and Ava.