All published SDs, are governed by copyright protection but the permission and restrictions may vary for each SDO. It is important to read the copyright statement and terms of service for each SD and ask a Librarian for help if you have questions. Some common copyright policies:
The Library is available to answer any questions you may have regarding intellectual property including copyright, fair use, and dissemination of information. Please contact us if you have questions
Talk with your professor regarding which citation style to use. Just like any other citation, you want to include as much information as you have that will allow others to find the exact same resource - such as SGO, alpha-numeric code, version, name of SD, when/where it's been accessed.