  Question Answering (QA) systems are becoming the inspiring model for the
future of search engines. While recently, underlying datasets for QA systems
have been promoted from unstructured datasets to structured datasets with
highly semantic-enriched metadata, but still question answering systems involve
serious challenges which cause to be far beyond desired expectations. In this
paper, we raise the challenges for building a Question Answering (QA) system
especially with the focus of employing structured data (i.e. knowledge graph).
This paper provide an exhaustive insight of the known challenges, so far. Thus,
it helps researchers to easily spot open rooms for the future research agenda.
