While creating a property you can set certain constraints to it. Constraints like - I want my username and password to be mandatory, my username to be unique, and the minimum length of my password should be 6, can be provided when you are creating the properties. These constraints are of 4 types:
1. Length constraints
2. Unique property constraints
3. Mandatory property constraints
4. Multi-valued property constraints
5. Setting a property as the identifier property.