Table queries unified into a single file/class
Database system contracts reinforced

Switching uses of concrete classes of Database and DatabaseSystem with
their contracts (for future extensibility)
DatabaseConnection contract reinforced

In the view of a new modular system, we removed the binding to the
concrete DatabaseConnection object, replacing with the contract
DatabaseConnection abstracted to the contract
Reorganization of the Index Models

Refactoring and reorganization of the indexing/searching model of the
system (moving classes and objects around namespaces and redefinition of
Index logic)