C#: semantic networks with default reasoning

A semantic network represents knowledge as nodes joined by links such as is-a. Properties attach to nodes, and a node inherits properties from its ancestors. Looking up a property means walking up the is-a chain until some node defines it.

using System;
using System.Collections.Generic;

class Node {
  public string Name;
  public Node Parent;
  public Dictionary<string, bool> Properties = new Dictionary<string, bool>();

  public Node(string name, Node parent) {
    Name = name;
    Parent = parent;
  }

  public bool? Lookup(string property) {
    for (Node n = this; n != null; n = n.Parent) {
      if (n.Properties.TryGetValue(property, out bool value)) {
        return value;
      }
    }
    return null;
  }
}

class Program {
  static void Main() {
    var animal = new Node("animal", null);
    animal.Properties["alive"] = true;
    var bird = new Node("bird", animal);
    bird.Properties["flies"] = true;
    bird.Properties["feathers"] = true;
    var penguin = new Node("penguin", bird);
    penguin.Properties["flies"] = false;
    var tweety = new Node("tweety", bird);
    var opus = new Node("opus", penguin);

    foreach (var (node, property) in new[] { (tweety, "flies"), (opus, "flies"), (opus, "feathers"), (opus, "swims") }) {
      Console.WriteLine(node.Name + " " + property + ": " + (node.Lookup(property)?.ToString() ?? "unknown"));
    }
  }
}

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