lease provide a comprehensive solution for the transformation of this invoice system, encompassing the entire normalization process $($from Unnormalized Form $-$ UNF, to First Normal Form $-1$NF$,$ Second Normal Form $-2$NF$,$ and Third Normal Form $-3$NF$).$ Additionally, create an Entity$-$Relationship Diagram $($ERD$)$ to visually represent the database structure. Furthermore, detail the implementation of a cursor to iterate through relevant data, a trigger to automate specific actions in response to database events, and a function to encapsulate a specific computation or logic within the context of this invoicing system. Your thorough response will assist in understanding the normalization steps, the database schema, and the practical implementation of key database components, providing a comprehensive overview of the entire process.