The man behind the Harry Potter Lexicon book has broken down on the witness stand in the trial against his idol JK Rowling.Steven Vander Ark wiped away tears on the second day of evidence when he was asked to reflect on what the case has done to his relationship with the community of Potter fans around the world.Rowling is suing his publisher RDR Books and trying to prevent the publication of the encyclopedia based on Vander Ark's fan website, claiming it infringes on her copyright by borrowing too heavily from her novels.During his testimony, Vander Ark acknowledged that he had concerns about whether publishing the book would constitute copyright infringement. He also said he was talked into doing it by the publishing company.Rowling testified on Monday that the Harry Potter characters she created were "as dear as her children". She revealed she had recently started work on her own encyclopedia but said if Vander Ark's lexicon is published, she would not have the "will or the heart to continue" it.But RDR lawyer Anthony Falzone defended the lexicon as a reference guide, calling it a legitimate effort to organise the world of Harry Potter. The small publisher is not contesting that the lexicon infringes upon Rowling's copyright but argues that it is a fair use allowable by law for reference books.The testimony and arguments could last most of the week.The trial comes eight months after the publication of Rowling's final book in the series, Harry Potter and the Deathly Hallows.The seven books have been published in 64 languages, sold more than 400 million copies and produced a multi-billion pound film franchise.