Ethical issues related to patents are relevant to particular research groups that develop technology which may be relevant for patent applications. Sharing research data by depositing it in connection with a published article or otherwise making data publicly available sometimes raises intellectual property questions. While 'facts' cannot be copyrighted, most source materials used by historians are original works in their own right and, unless old enough to have entered the public domain, are likely to be covered by copyright law. Copyright does not merely apply to printed or formally published works: it includes, for example, manuscripts, letters, and recordings of interviews.