<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Archiving and Interchange DTD v1.0 20120330//EN" "JATS-archivearticle1.dtd">
<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Towards an affective tutoring system with multimedia content adaptation</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Arlem García</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Aleida Castillo-Avila</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Manuel Gonzalez-Calleros</institution>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>and Josefina Guerrero-</institution>
        </aff>
      </contrib-group>
      <abstract>
        <p>Adaptation allows for the personalization of learning through the use of different strategies, for example, the adaptation of multimedia content. An Affective Tutoring System (ATS) adapts the learning process to the emotions presented by the student during the interactive session. However, the development of intelligent tutor systems has become more complex. One problem is the lack of consensus about standards for their implementation, which makes it difficult to generalize their effectiveness. In this research, we propose a model-based development architecture for an ATS that adapts multimedia content in the presence of different levels of anxiety, with the aim of being able to extend its application to multiple learning domains.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;ITS</kwd>
        <kwd>ATS</kwd>
        <kwd>e-learning design</kwd>
        <kwd>personalized learning</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Learning is not only associated with the cognitive context of the student but also with other factors
such as their personality and emotions. Within the classroom the teacher influences the emotional state
of the students and this in turn influences the effectiveness of the process [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. However, each person
experiences a different reaction to the same situation; therefore, decision making regarding pedagogical
activities, thematic content, and presentation of the learning strategy will not have the same effect for
an entire work group. A particularity of specific learning disorders and deficiencies in the area of
mathematical didactics is the influence that the affective state has on the process. Mathematical anxiety
is an example of a persistent emotion in students who face difficulties in carrying out any type of
problem involving the use of mathematical knowledge. Among the characteristics of its treatment in a
traditional way is the importance of fostering motivation and decreasing anxiety and frustration through
personalized learning.
      </p>
      <p>
        Personalized learning mediated by technology allows us to recognize and respond to different
particular factors of users, such as the affective state at a specific time. An Intelligent Tutoring System
(ITS) is a technological tool that can collect information from the learner and adapt the instruction to
the learner’s needs [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. Specifically, an Affective Tutoring System (ATS) adapts its response to the
emotions presented by the learner during the interactive session [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ].
      </p>
      <p>
        Despite the extensive development in the research and creation of ATS, in many cases the possibility
of reusing these tools has been limited [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ] [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. One of the factors influencing this limitation is the need
to analyze the ATS requirements from the software development perspective, considering that the
implementation should be agnostic to the technology and the learning domain, but not to the learning
objective.
      </p>
      <p>
        In ITS development, the best known approaches are the client-server architecture and the component
architecture [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ] [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ] [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ][
        <xref ref-type="bibr" rid="ref9">9</xref>
        ]. All are based on the basic model of an ITS, which is composed of 3 main
modules and a final user interface, as shown in the Figure 1. Despite the effectiveness of the abstract
model, there are many software functionalities that are not represented in it. For this reason, the
development of an ATS almost always involves a double design stage. On the one hand, obtaining the
competent elements of the basic model of an ITS; and on the other hand, software engineering process.
      </p>
      <p>
        In [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ], the authors propose a 5-layer architecture based on the basic components of an ITS that aims
to address the need for ITS development whose effectiveness is replicable to different learning contexts.
However, it still separates the definition of learning objectives and instructional design from the
implementation of the software system.
      </p>
      <p>
        On the other hand, there are methodologies for the development of instructional design that take up
the stages of classical software engineering methodologies, such as the ADDIE model [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. The
disadvantage is that, although it makes a more explicit connection between the software and the
learning process, it still separates the process of defining the domain and the system.
      </p>
      <p>
        This research proposes the development of an ATS that takes into account the learner’s levels of
anxiety, using a methodology based on the CAMELEON framework [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ]. The objective is to develop
a tool that adapts the multimedia content to the affective needs of the user, that can be reusable in
different learning contexts, and that the development process unifies the definition of the objectives,
elements of the learning process, and the software requirements. The general description of the
proposed ATS is showed in Figure 2.
      </p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Work</title>
      <p>
        Research on ATS has been conducted from three main approaches. On the one hand, a set of studies
oriented to the identification of emotions in learning from the use of ITS [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. Another approach has
been the development of emotion measurement methods, which are classified into verbal methods,
based on text and voice evaluation [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ] [
        <xref ref-type="bibr" rid="ref14">14</xref>
        ], and nonverbal methods, such as face analysis and
biosignals such as heart rate or neural activity [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ]. A final approach has been given regarding the
explanation of emotions in the technology-mediated educational context [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ]. The latter is the most
recent and with a smaller number of contributions to date. However, in the development of ATS, one
of the largest referents is the multimedia cognitive theory of learning [
        <xref ref-type="bibr" rid="ref17">17</xref>
        ], which relates the stimulus
derived from multimedia content to the creation of models in working memory and the integration of
previous knowledge in long-term memory.
      </p>
      <p>Considering the distribution of studies with respect to research approaches, a need to test the effect
on the learning process in different contexts becomes evident. It should also be mentioned
that the number of research from Latin American countries is minimal. The effectiveness of these tools
in different contexts needs to be reported, since variations among users lead to different results that
should be considered in the improvement of their development at the technological level.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Model Driven Architecture based methodology</title>
      <p>For the development of the ATS that adapts the multimedia content, a methodology based on the use
of the model-driven architecture (MDA) is proposed. The development of virtual environments faces
increasing difficulties that have been attacked using the model-driven architecture (MDA), this
architecture contemplates four basic components for the development of interactive systems: models,
language, software and approach. MDA separates the conceptual design, which concretizes the
functionality, as a platform independent model (PIM), from the corresponding implementation as
platform specific models (PSM). All of them from a computation-independent model (CIM) (Figure
3).</p>
      <p>
        The approach used is UsiXML [
        <xref ref-type="bibr" rid="ref18">18</xref>
        ] which is based on the CAMELEON Framework. This
framework, in turn, consists of four development phases, namely:
• TasksandConcepts(TC): describe the user tasks, the concepts related to the data model
(concepts) that are required to perform these tasks.
• Abstract User Interface (AUI): defines abstract containers and individual interaction
components. Tasks are associated to containers for execution or to individual objects for
manipulation. An AUI is considered as an abstraction of a concrete user interface with respect
to the interaction modality. At this level, the user interface consists mainly of the definition of
inputs and outputs of the system but nothing is defined about the interaction modality (graphical,
voice, touch).
• Concrete user interface (CUI): the concrete interface defines an interaction modality and as
such the interface is composed of elements that describe it, concrete interaction objects (CIOs)
in order to define the interface design and navigation widgets. The CUI is independent of any
computing platform, although it makes explicit the appearance and behavior of an end-user
interface, it is still a mock-up, which only works within a particular environment. A CUI can
also be considered as a reification of an AUI at the top level and an abstraction of the end user
interface with respect to the platform.
• Fine User Interface (FUI): is the operational part, i.e., the running user interface on a computing
platform.
      </p>
      <p>Transformational user interface development finds its motivations in the concept of heterogeneity
of information systems. In this case, heterogeneity refers to the variety of contexts of use for which a
user interface has been designed. This heterogeneity emphasizes the need to be able to rely on the
abstraction of details relevant to specific contexts. From these abstractions, it is possible to obtain
specific representations. The advantage of accessing such representations is to be able to reason about
a single (task) model and to obtain many different user interfaces. In the Figure 4 it is showed the
layers of the CAMELEON framework.</p>
    </sec>
    <sec id="sec-4">
      <title>4. ATS software architecture and development of a communication API.</title>
      <p>In order to make the ATS development extensible, a set of services was developed that communicate
with each other to provide general functionalities and support future specific functionalities. The
general scheme is shown in the Figure 5. The modular design allows the software to be used in
experimental environments, under conditions not yet fully defined. There is an ”Interaction” layer,
consisting of a client that serves as an interface for users. The ”General Functionality” layer is
responsible for exposing the API input to the system, registering new Domain modules, making use of
the data processing that these Domains provide, and mediating between these modules to store data in
the Persistence layer. The ”Specific Functionality” layer is a specialized service that contains what is
needed to define a system task with specific objectives, the data schema of that task and the algorithms
needed to process it. Finally, there is a ”Persistence” layer that is responsible for storing the data for
storage and post-processing. Its main component is the database.</p>
    </sec>
    <sec id="sec-5">
      <title>5. ATS implementation: supporting learning of algebra</title>
      <p>An ATS to support the learning process for students taking high school algebra courses, using the
proposed methodology, has been developed.The system is composed of four independent modules. A
tutor module, which manages the interactive activities and processes; a student module, which analyzes
and responds to the user’s data and needs; a domain module, which contains the educational resources
pertaining to the subject; and finally, a final user interface that allows the student to interact with the
system. The main flow of the designed system is described in Figure 6 The user can make use of
different activities designed in the system that allow him to enrich his knowledge in the fundamentals
of algebra, taking account his emotional state, mainly the mathematical anxiety that he may present
during the sessions. The user interface was developed to make the use of the system simple, accessible
and satisfactory in relation to the educational objectives it supports. Some examples of the final user
interfaces are showed in Figure 7. The tests developed in this study will serve as a basis for improving
the design of the system, as well as the teaching strategies that compose it.</p>
    </sec>
    <sec id="sec-6">
      <title>6. Preliminary conclusions and future work</title>
      <p>From the perspective of user-centered interface design, it is possible to integrate the general elements
that constitute an ITS to support the general model and also specific needs, such as adaptation to the
learner’s emotions.
Following a proper construction of the interaction flow and from the abstractions of the user tasks, the
software implementation and the learning objectives can be worked at the same time, which reduces
the development time of this type of educational technology. The presentation of the UI directly
influences the effectiveness of the pedagogical strategy when using educational systems, since the
student takes the role of the end user for whom we must design and evaluate the UX.</p>
      <p>As a case study to validate the tool, a study of its effect on the academic performance of a group of
high school algebra students in the context of the city of Puebla, Mexico, will be carried out. For this
study, users must have an electronic device with internet access, either by Wifi or mobile data, and that
has a webcam (computer, tablet or cell phone). Each user will perform a total of 5 interactive sessions
with the tutor system over the course of a week. During the first session, the system will perform a
knowledge diagnosis to place the user in the activities of the corresponding level within the subject
matter. Subsequently, an evaluation of the level of anxiety at the beginning of the training will be
performed. During the learning activities, the system will record information about the user, through
short questions and video camera monitoring.</p>
      <p>The activities to be performed in the interactive sessions will be described at the beginning of each
one, since they will be selected as a change in the affective and cognitive state of the student is
detected. At the end of the week, the user will carry out an evaluation of knowledge on the topic
addressed, as well as an evaluation of the system, by means of a questionnaire of 10 short questions.
The system will update the level of anxiety observed and present the user with a final written
evaluation.</p>
      <p>From the result of this first software validation, we will be able to extend the context of use of the
system to other learning domains, with heterogeneous user groups.</p>
      <p>Figure 7: ATS final user interfaces</p>
    </sec>
  </body>
  <back>
    <ref-list>
      <ref id="ref1">
        <mixed-citation>
          [1]
          <string-name>
            <given-names>R.</given-names>
            <surname>Mohanan</surname>
          </string-name>
          ,
          <string-name>
            <given-names>C.</given-names>
            <surname>Stringfellow</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Gupta</surname>
          </string-name>
          ,
          <article-title>An emotionally intelligent tutoring system</article-title>
          ,
          <source>in: 2017 Computing Conference</source>
          , IEEE,
          <year>2017</year>
          , pp.
          <fpage>1099</fpage>
          -
          <lpage>1107</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref2">
        <mixed-citation>
          [2]
          <string-name>
            <given-names>M. H. F.</given-names>
            <surname>Zarandi</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Khademian</surname>
          </string-name>
          ,
          <string-name>
            <given-names>B.</given-names>
            <surname>Minaei-Bidgoli</surname>
          </string-name>
          , et al.,
          <article-title>A fuzzy expert system architecture for intelligent tutoring systems: A cognitive mapping approach</article-title>
          ,
          <source>Journal of Intelligent Learning Systems and Applications</source>
          <volume>4</volume>
          (
          <year>2012</year>
          )
          <fpage>29</fpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref3">
        <mixed-citation>
          [3]
          <string-name>
            <given-names>M. A.</given-names>
            <surname>Hasan</surname>
          </string-name>
          ,
          <string-name>
            <given-names>N. F. M.</given-names>
            <surname>Noor</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S. S. B. A.</given-names>
            <surname>Rahman</surname>
          </string-name>
          ,
          <string-name>
            <surname>M. M. Rahman</surname>
          </string-name>
          ,
          <article-title>The transition from intelligent to affective tutoring system: a review and open issues</article-title>
          ,
          <source>IEEE Access 8</source>
          (
          <year>2020</year>
          )
          <fpage>204612</fpage>
          -
          <lpage>204638</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref4">
        <mixed-citation>
          [4]
          <string-name>
            <given-names>N. T.</given-names>
            <surname>Graf von Malotky</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Martens</surname>
          </string-name>
          ,
          <article-title>General its software architecture and framework</article-title>
          ,
          <source>in: International Conference on Intelligent Tutoring Systems</source>
          , Springer,
          <year>2020</year>
          , pp.
          <fpage>17</fpage>
          -
          <lpage>22</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref5">
        <mixed-citation>
          [5]
          <string-name>
            <given-names>A. A.</given-names>
            <surname>Castillo Avila</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J. M.</given-names>
            <surname>González Calleros</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J. Guerrero</given-names>
            <surname>García</surname>
          </string-name>
          , Revisión sistemática de la literatura sobre los sistemas tutores afectivos:
          <fpage>2001</fpage>
          -
          <lpage>2020</lpage>
          , Revista Brasileira de Informática na Educação
          <volume>29</volume>
          (
          <year>2021</year>
          )
          <fpage>928</fpage>
          -
          <lpage>956</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref6">
        <mixed-citation>
          [6]
          <string-name>
            <given-names>S. A.</given-names>
            <surname>Kazi</surname>
          </string-name>
          ,
          <string-name>
            <surname>Vocatest:</surname>
          </string-name>
          <article-title>An intelligent tutoring system for vocabulary learning using the” mlearning” approach (</article-title>
          <year>2005</year>
          ).
        </mixed-citation>
      </ref>
      <ref id="ref7">
        <mixed-citation>
          [7]
          <string-name>
            <given-names>P.</given-names>
            <surname>Dašić</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Dašić</surname>
          </string-name>
          ,
          <string-name>
            <given-names>B.</given-names>
            <surname>Crvenković</surname>
          </string-name>
          ,
          <string-name>
            <given-names>V.</given-names>
            <surname>Šerifi</surname>
          </string-name>
          ,
          <article-title>A review of intelligent tutoring systems in e-learning,</article-title>
          <source>Annals of the University of Oradea</source>
          <volume>3</volume>
          (
          <year>2016</year>
          )
          <fpage>85</fpage>
          -
          <lpage>89</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref8">
        <mixed-citation>
          [8]
          <string-name>
            <surname>I. Padayachee</surname>
          </string-name>
          ,
          <article-title>Intelligent tutoring systems: Architecture and characteristics</article-title>
          ,
          <source>in: Proceedings of the 32nd Annual SACLA Conference</source>
          , Citeseer,
          <year>2002</year>
          , pp.
          <fpage>1</fpage>
          -
          <lpage>8</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref9">
        <mixed-citation>
          [9]
          <string-name>
            <given-names>S.</given-names>
            <surname>Dutt</surname>
          </string-name>
          ,
          <string-name>
            <given-names>N. J.</given-names>
            <surname>Ahuja</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Kumar</surname>
          </string-name>
          ,
          <article-title>An intelligent tutoring system architecture based on fuzzy neural network (fnn) for special education of learning disabled learners</article-title>
          ,
          <source>Education and Information Technologies</source>
          <volume>27</volume>
          (
          <year>2022</year>
          )
          <fpage>2613</fpage>
          -
          <lpage>2633</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref10">
        <mixed-citation>
          [10]
          <string-name>
            <given-names>A. L. L.</given-names>
            <surname>Cruces</surname>
          </string-name>
          , F. De Arriaga,
          <article-title>Reactive agent design for intelligent tutoring systems</article-title>
          ,
          <source>Cybernetics &amp; Systems</source>
          <volume>31</volume>
          (
          <year>2000</year>
          )
          <fpage>1</fpage>
          -
          <lpage>47</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref11">
        <mixed-citation>
          [11]
          <string-name>
            <given-names>B. A.</given-names>
            <surname>Jones</surname>
          </string-name>
          ,
          <article-title>Addie model (instructional design) (</article-title>
          <year>2014</year>
          ).
        </mixed-citation>
      </ref>
      <ref id="ref12">
        <mixed-citation>
          [12]
          <string-name>
            <given-names>G.</given-names>
            <surname>Calvary</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Coutaz</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Bouillon</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Florins</surname>
          </string-name>
          ,
          <string-name>
            <given-names>Q.</given-names>
            <surname>Limbourg</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Marucci</surname>
          </string-name>
          ,
          <string-name>
            <given-names>F.</given-names>
            <surname>Paternò</surname>
          </string-name>
          ,
          <string-name>
            <given-names>C.</given-names>
            <surname>Santoro</surname>
          </string-name>
          ,
          <string-name>
            <given-names>N.</given-names>
            <surname>Souchon</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Thevenin</surname>
          </string-name>
          , et al.,
          <source>The cameleon reference framework, deliverable 1.1, version v1. 1</source>
          ,
          <string-name>
            <surname>cameleon</surname>
            <given-names>project</given-names>
          </string-name>
          (
          <year>2002</year>
          <article-title>) campbell</article-title>
          , e.,
          <article-title>maintaining accessible websites with microsoft word and xml</article-title>
          ,
          <source>in: Proceedings of XML Europe</source>
          ,
          <year>2003</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref13">
        <mixed-citation>
          [13]
          <string-name>
            <given-names>R. Z.</given-names>
            <surname>Cabada</surname>
          </string-name>
          ,
          <string-name>
            <surname>M. L. B. Estrada</surname>
            ,
            <given-names>F. G.</given-names>
          </string-name>
          <string-name>
            <surname>Hernández</surname>
            ,
            <given-names>R. O.</given-names>
          </string-name>
          <string-name>
            <surname>Bustillos</surname>
          </string-name>
          ,
          <article-title>An affective learning environment for Java</article-title>
          ,
          <source>in: 2015 IEEE 15th International Conference on Advanced Learning Technologies, IEEE</source>
          ,
          <year>2015</year>
          , pp.
          <fpage>350</fpage>
          -
          <lpage>354</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref14">
        <mixed-citation>
          [14]
          <string-name>
            <surname>J. M. Martin</surname>
            ,
            <given-names>A.</given-names>
          </string-name>
          <string-name>
            <surname>Ortigosa</surname>
            ,
            <given-names>R. M.</given-names>
          </string-name>
          <string-name>
            <surname>Carro</surname>
          </string-name>
          , SentBuk:
          <article-title>Sentiment analysis for e-learning environments</article-title>
          , in: 2012
          <source>International Symposium on Computers in Education (SIIE)</source>
          , IEEE,
          <year>2012</year>
          , pp.
          <fpage>1</fpage>
          -
          <lpage>6</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref15">
        <mixed-citation>
          [15]
          <string-name>
            <given-names>I.</given-names>
            <surname>Arroyo</surname>
          </string-name>
          ,
          <string-name>
            <given-names>B. P.</given-names>
            <surname>Woolf</surname>
          </string-name>
          ,
          <string-name>
            <given-names>W.</given-names>
            <surname>Burelson</surname>
          </string-name>
          ,
          <string-name>
            <given-names>K.</given-names>
            <surname>Muldner</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Rai</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Tai</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A Multimedia</given-names>
            <surname>Adaptive</surname>
          </string-name>
          <article-title>Tutoring System for Mathematics that Addresses Cognition, Metacognition</article-title>
          and Affect,
          <source>International Journal of Artificial Intelligence in Education</source>
          <volume>24</volume>
          (
          <year>2014</year>
          )
          <fpage>387</fpage>
          -
          <lpage>426</lpage>
          . URL: http: //link.springer.com/10.1007/s40593-014-0023-y. doi:
          <volume>10</volume>
          .1007/s40593-014-0023-y.
        </mixed-citation>
      </ref>
      <ref id="ref16">
        <mixed-citation>
          [16]
          <string-name>
            <given-names>R. E.</given-names>
            <surname>Mayer</surname>
          </string-name>
          ,
          <article-title>Searching for the role of emotions in e-learning (</article-title>
          <year>2019</year>
          )
          <article-title>3</article-title>
          .
        </mixed-citation>
      </ref>
      <ref id="ref17">
        <mixed-citation>
          [17]
          <string-name>
            <surname>R. E. Mayer,</surname>
          </string-name>
          <article-title>The promise of multimedia learning: using the same instructional design methods across different media</article-title>
          ,
          <source>Learning and instruction 13</source>
          (
          <year>2003</year>
          )
          <fpage>125</fpage>
          -
          <lpage>139</lpage>
          .
        </mixed-citation>
      </ref>
      <ref id="ref18">
        <mixed-citation>
          [18]
          <string-name>
            <given-names>Q.</given-names>
            <surname>Limbourg</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Vanderdonckt</surname>
          </string-name>
          ,
          <string-name>
            <given-names>B.</given-names>
            <surname>Michotte</surname>
          </string-name>
          ,
          <string-name>
            <given-names>L.</given-names>
            <surname>Bouillon</surname>
          </string-name>
          ,
          <string-name>
            <given-names>V.</given-names>
            <surname>López-Jaquero</surname>
          </string-name>
          ,
          <article-title>Usixml: A language supporting multi-path development of user interfaces</article-title>
          ,
          <source>in: IFIP International Conference on Engineering for Human-Computer Interaction</source>
          , Springer,
          <year>2004</year>
          , pp.
          <fpage>200</fpage>
          -
          <lpage>220</lpage>
          .
        </mixed-citation>
      </ref>
    </ref-list>
  </back>
</article>