[FEATURE] Modify coding style in base module

[BECATRUE]

Feature you want to implement

I want to update the coding style (e.g. variable name, docstring) in swift.base module same as swift.bus module.

How the feature is implemented

• variable name: If it is private, the name starts '_' (underscore).
• docstring: Start with the singular form of the verb.

[kangz12345]

How about changing the name of the module base -> logic?