It does not represent past action. The action is ongoing.
Student or Learner
I've worked here for four years.
the above line gives the meaning of i am working even now also from past 4 years? Whether it represents unfinished/finished past action?
There is no difference between "I've been working here" and "I've worked here" in terms of whether it's still going on. There may be a difference in mindset, with the progressive POSSIBLY feeling newer or temporary or less likely to continue.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
"I've worked here" - The action is ongoing
"I've missed my flight" - It seems the action was completed
Both seems to be same structure (present perfect). if both actions is right, then how we distinguish which is finished and unfinished action?
I think the action has finished in 'I have read the book', but I am not a teacher.
Can the action be complete in 'I've worked here for years but now I have to quit'?