Refactoring

[PhilippeGalvan]

Following recent updates I suggest the following changes:

Refactor some expressions Update validation Enforce strict int validation as explained in:

• https://github.com/samuelcolvin/pydantic/issues/578

• https://pydantic-docs.helpmanual.io/usage/models/\#data-conversion

  Separate immutable 'object_values' from mutable 'entities' (see: https://medium.com/inato/an-introduction-to-domain-driven-design-386754392465 for a quick insight into Domain Driven Design which encapsulate the concepts of object values and entities). Apply some linting

[UPetit]

Fix dead link for pydantic data conversion: https://pydantic-docs.helpmanual.io/usage/models/#data-conversion