1. Agosti, M., Ferro, N.: A formal model of annotations of digital content. ACM Trans. Inform. Syst. 26(1), Article 3 (2007)
2. Andrews, P., Zaihrayeu, I., Pane, J.: A classification of semantic annotation systems. Semant. Web J. 3(3), 223–248 (2012)
3. Azouaou, F., Mokeddem, H., Berkani, L., Ouadah, A., Mostefai, B.: WebAnnot: learner’s dedicated web–based annotation tool. Int. J. Technol. Enhanced Learn. 5(1), 56–84 (2013)
4. Barret, A., Celevenger, J., Martini, J.: Open Sourcing Harvard University’s Collaborative Annotation Tool. Academic Technology Services, Harvard University (2013)
5. Carmichael, P.: Learning how to learn: using the Dublin Core metadata element set to support teachers as researchers. In: Proceedings of the International Conference on Dublin Core and Metadata Applications: Metadata for e-Communities: Supporting Diversity and Convergence, pp. 201–203 (2002)