title: Modeling Item Size in Rails App
body: <p>I have an Item model, that can be clothing, shoes, or bags (category).
  I also have the Size model, that represents the Size of the Item.</p>
  
  <p>The issue is:
  For clothing, size can be: XS, S, M, L, XL
  For shoes, size can be: 9, 9.5, 10, 10.5</p>
  
  <p>Also, the shoe size depends if it is UK or US or European, so a UK 6 is a US 7 and European 40.</p>
  
  <p>How should I model this?
  Everything as a single Size model?
  Should I have child models?
  Or should I have many different models (ShoeSize, ClothingSize)?</p>
  
  <p>Thanks in advance.</p>