OCL and Model Validation

[logicchopper]

I want to add OCL expressions to my models.  What I'm interested in specifically is what the Model Validation in EA actually checks.  For example, if I specify that I cannot have more than 3 objects of type A connected to 1 object of type B, do I put the OCL expression into the classifier for A or B?  Is this then checked when I create an object diagram showing A and B and the relationship between them?  How do OCL expressions match up to the EA diagrams and elements?