# Recommending Learning Objects with Arguments and Explanations
## 3 Conversational Educational Recommender System (C-ERS)
### Recommendation Process
\begin{table}
\begin{tabular}{l} \hline _C1.2: generally\_appropriate(LO) \(\leftarrow\)structure(LO, atomic) \(\wedge\) state(LO, final)_ \\ Explanation: **’This LO may interest you, since it is self-contained’** \\ Responses: \\ **+RC1.2: ‘Accept’** \\ \(\sim\)**RC1.2: ‘Not sure. I do not care about the LO is not self-contained’** \\ \(\sim\)**RC1.2: ‘Reject. I don’t like it’** \\ \hline _C2: recommend(user, LO)\(\leftarrow\) educationally\_appropriate(user, LO) \(\wedge\) generally\_appropriate(LO) \(\wedge\) technically\_appropriate(user, LO)_ \\ \hline C2.1: technically\_appropriate(user, LO) \(\leftarrow\) appropriate\_language(user, LO) \(\wedge\) appropriate\_format(LO)_ \\ \hline C2.1.1: _appropriate\_language(user, LO) \(\leftarrow\) language\_preference(user, language) \(\wedge\) object\_language(LO, language)_ \\ Explanation: **’This LO may interest you, since it suits your language preferences: [OBJECT\_LANGUAGE]** \\ Responses: \\ **+RC2.1.1: ‘Accept’** \\ \(\sim\)**RC2.1.1: ‘Not sure. Show me more reasons’** \\ **-RC2.1.1: ‘Reject. I prefer LOs in [LANGUAGE]** \\ \hline _C2.1.2: appropriate\_format(LO) \(\leftarrow\) format\_preference(user, format) \(\wedge\) object\_format(LO, format)_ \\ Explanation: **’This LO may interest you, since it suits your format preferences: [OBJECT\_FORMAT]** \\ Responses: \\ **+RC2.1.2: ‘Accept’** \\ \(\sim\)**RC2.1.2: ‘Not sure. Show me more reasons’** \\ **-RC2.1.2: ‘Reject. I prefer LOs with format [OBJECT\_FORMAT]** \\ \hline _C3: recommend(user, LO) \(\leftarrow\) educationally\_appropriate(user, LO) \(\wedge\) generally\_appropriate (LO) \(\wedge\) updated(LO)_ \\ \hline _C3.1: updated(LO) \(\leftarrow\) date(LO, date) \(<\) 5 years_ \\ Explanation: **’This LO may interest you, since it is updated’** \\ Responses: \\ **+RC3.1: ‘Accept’** \\ \(\sim\)**RC3.1: ‘Not sure. I do not care that the LO is not updated’** \\ **-RC3.1: ‘Reject. I don’t like it’** \\ \hline _C4: recommend(user, LO) \(\leftarrow\) educationally\_appropriate(user, LO) \(\wedge\) generally\_appropriate(LO) \(\wedge\) learning\_time\_appropriate(LO)_ \\ \hline _C4.1: learning\_time\_appropriate(LO) \(\leftarrow\) hours(LO) \(<\) \(\gamma\)_ \\ Explanation: **’This LO may interest you, since it suits your learning time preferences (less than \(\gamma\)) hours to use it’** \\ Responses: \\ **+RC4.1: ‘Accept’** \\ **+RC4.1: ‘Not sure. Now the more reason’** \\ **-RC4.1: ‘Reject. I don’t like it’** \\ \hline _Collaborative Rules_ \\ _O1: recommend(user, LO) \(\leftarrow\) similarity(user, user\({}_{k}\)) \(>\) \(\alpha\) \(\wedge\) vote(user\({}_{k}\), LO) \(\geq\) 4_ \\ Explanation: **’This LO may interest you, since it likes to users like you’** \\ Responses: \\ **+RO1: ‘Accept’** \\ \(\sim\)**ROI: **’Not sure. Show me more reasons’** \\ **-RO1: ‘Reject. I don’t like it’** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Cont. In addition, line 14 represents a _collaborative rule_ that takes information from the students' profile to calculate a similarity degree among them and recommends an LO that was suitable for a similar student _pau_l. Finally, line 15 represents a _knowledge-based rule_ that uses information about other LO which the user has already evaluated previously to make a recommendation of a similar LO: \(LO_{2}\). Note that, although the fact _vote(alice, LO)_\(\geq\) 4 does not appear in the example logic program, in the proposed defeasible argument, formalism is not assumed negation as failure. We follow the approach of extended logic programming for non-monotonic reasoning, as proposed in [38], by allowing, in addition to negation as failure, a second, explicit form of negation, written as \(\sim\). Therefore, the non-existence of a fact does not prevent the triggering of those rules that include it and, hence, the knowledge-based rule of line 5 can be used to generate an argument that supports the recommendation of \(LO_{2}\). Afterwards, rules can be defeated by the inclusion of new knowledge in the system.