# Variables
ErrBadParamInput will throw if the given request-body or params is not valid.
ErrConflict will throw if the current action already exists.
ErrInternalServerError will throw if any the Internal Server Error happen.
ErrNotFound will throw if the requested item is not exists.
# Interfaces
ArticleRepository represent the article's repository contract.
ArticleUseCase represent the article's usecases.
AuthorRepository represent the author's repository contract.