Annotations are defined as remarks, documents or, more generally, objects attached to a specific part of a document[1,2,3]. This part of the document is called the annotation anchor [2,3]. Marshall proposes several continuous dimensions of annotations that reflect their attributes [4]:

• explicit vs tacit
• annotation as writing vs annotation as reading
• Hyperextensive v. extensive v. intensive annotation
• Permanent v. transient annotations
• Published v. private
• Global v. institutional v. workgroup v. personal

Desmoulins & Mille further emphasize the importance of the annotator's intent and explicate that, without the annotated document, the annotation has no meaning. They propose the structure of an annotations as consisting of „an anchor, a visual form, a context, a value and an access“ [5].

Besides physical annotations, which are also called personal annotations [4], there are also digital annotations, which means that a digital tool gives the user the option to annotate digital content [1]. Some digital tools enable the user to share their annotations with other users, such tools are called social annotation tools [1].

In this project we only analyze personal annotations. We maybe also compare social annotation tools but only for their ability to make personal annotations.

In this Project we define a Annotation Tools as a Tool which gives the User the option to read a document, make annotations to the document and save the current state of the document. For digital documents, PDF is the de facto standard.

• physical tools (printed document, pen, ruler…)
• Adobe Acrobat Reader (desktop & mobile)
• Foxit Reader (desktop & mobile)
• Preview (macOS)
• Xodo (desktop & mobile, touchscreen focused)
• Drawboard PDF (desktop & tablet, touchscreen focused)
• smallpdf.com (web browser)
• pdf2go.com (web browser)

Cursory market research reveals that many PDF readers come with very similar annotation features (highlighting, underline, strike through, shape drawing, free-form drawing, attaching notes etc.). Most offer these tools for free, while more in depth-editing of PDFs or cloud support & collaboration features are paid services. PDF annotation may differ in platform availability or target devices (Drawboard PDF and Xodo for instance where designed for touchscreen devices, Adobe Acrobat and Foxit reader are traditionally desktop software which now support touch input). There are also online personal document annotation solutions which only require a web browser with JavaScript enabled and can thus be considered cross-platform (smallpdf.com, pdf2go.com).

[1] Krouska, A., Troussas, C., & Virvou, M. (2018). Social Annotation Tools in Digital Learning: A Literature Review. 2018 9th International Conference on Information, Intelligence, Systems and Applications (IISA), 1–4. https://doi.org/10.1109/IISA.2018.8633609

[2] Giordano, D., & Mineo, S. (2005). A graphical annotation platform for web-based e-learning. Proc. of Multimedia and Information and Communication Technologies in Education, 1255-1260.

[3] Desmontils, E., Jacquin, C., & Simon, L. (2004). Dinosys: An Annotation Tool for Web-Based Learning. In W. Liu, Y. Shi, & Q. Li (Hrsg.), Advances in Web-Based Learning – ICWL 2004 (Bd. 3143, S. 59–66). Springer Berlin Heidelberg. https://doi.org/10.1007/978-3-540-27859-7_8

[4] Marshall, C. C. (1998). Toward an ecology of hypertext annotation. Proceedings of the Ninth ACM Conference on Hypertext and Hypermedia : Links, Objects, Time and Space—Structure in Hypermedia Systems Links, Objects, Time and Space—Structure in Hypermedia Systems - HYPERTEXT ’98, 40–49. https://doi.org/10.1145/276627.276632

[5] Desmoulins, C., & Mille, D. (2002). Pattern-based annotations on E-books: From personal to shared didactic content. Proceedings. IEEE International Workshop on Wireless and Mobile Technologies in Education, 82–85.