Question: when was the first book in jk rowling's harry potter series published
[{'answer': '26 June 1997', 'provenance': [{'wikipedia_id': '2387806', 'title': 'Harry Potter', 'start_paragraph_id': 2, 'start_character': 85, 'end_paragraph_id': 2, 'end_character': 97, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '2387806', 'title': 'Harry Potter', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 706, 'bleu_score': 0.721953119472959, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3568719562096838023}, 'section': 'Section::::Abstract.'}]}]