Refactor abstraction.py

[sdemarch]

Restructure the module abstraction.py to handle abstract interpretation objects and methods

• (perhaps) create new module for Star and StarSet classes
• Remove AbsNetwork classes, either move the forward and backwards entry points in the concrete network class or create new class for handling at a high level the abstracion flow
• Refactor functions into (weak-private) class methods for AbsLayerNodes now that Python allows to use multiprocessing on them

[darioguidotti]

It might make sense to transform AbsNeuralNetwork into a wholly abstract class, requiring the implementation of forward and backward methods. Subsequently, we would have AbsSeqNetwork and AbsAcyclicNetwork, both inheriting from AbsNeuralNetwork as well as their respective counterparts in networks.py (SequentialNetwork and AcyclicNetwork). This approach ensures the inheritance of all node management methods, mitigating redundancy in the codebase.

To make this approach work we will need to complete the planned refactoring in node.py (#24) and networks.py (#23).

[sdemarch]

Should it be the case that, instead of a method build_abs_network in verification.py, the same procedure is the abstract class constructor in abstraction.py? It is (and should) never the case that an abstract network is initialized without the complete concrete network.

TL;DR AbsSeqNetwork init method should contain the code of __build_abs_seq_network?

[sdemarch]

We decided to structure the module as follows:

• Make abstraction a package with submodules networks for abstract elements and networks, and layers for abstract layers
• Make a base class LayerNode with only the identifier as a parameter, and have AbsLayerNode and ConcreteLayerNode objects inherit from it (nodes.py). AbsLayerNode will contain a reference to their concrete counterpart, and the forward and backward methods (abstraction.layers.py).
• Make a base class NeuralNetwork representing a graph, and the classes SequentialNetwork and AcyclicNetwork as children specializing it (networks.py).
• Make an interface IAbstractNetwork to provide forward and backward methods to concrete classes AbsSequentialNetwork and AbsAcyclicNetwork which will inherit from the interface and their concrete counterpart.
• Make a Factory for abstract networks instead of directly instantiating them