1. Advanced Distributed Learning. (2013). xAPI-Spec. Retrieved from https://github.com/adlnet/xAPI-Spec/blob/1.0.0/xAPI.md .
2. Advanced Distributed Learning. (2015a). Case studies and adopters. Retrieved from http://www.adlnet.gov/tla/experience-api/adopters/ .
3. Advanced Distributed Learning. (2015b). Research and development focus. Retrieved from http://www.adlnet.gov/overview/#RandD .
4. Advanced Distributed Learning. (2015c). xAPI community of practice overview. Retrieved from http://www.adlnet.gov/tla/experience-api/xapi-cop-directory/overview/ .
5. Berking, P., & Gallagher, S. (2014). Choosing a learning management system (No. 3.13) (pp. 1–117). Advanced Distributed Learning.