Please keep aside sentence structure and focus on meaning
"having been + past participle"
passive structure used in participle clauses as an alternative to a since-clause:
1. "Having seen an accident ahead, I stopped my car."
Meaning I noticed that there had been an accident ahead and stopped my car.
2. Seeing an accident ahead, I stopped my car.
Meaning When I saw the accident ahead, I stopped my car.
Now read this sentence
"Having been unemployed for over two years, I found it difficult to get work."
"Having been shown into the office, Julia waited for the dentists to arrive."
see link http://www.bbc.co.uk/worldservice/learn ... v305.shtml
Hope It is clear to you.