## 5 Conclusions and Future Work
Both kinds of information are helpful for scientists to comprehend and navigate through the space of main research issues in scientific literature. As ICRT identifies clusters by clustering IITs, descriptive labels for a cluster \(c\) can be selected from IITs of article pairs in \(c\). _IITsrength_ defined above (ref. Equation (12)) can be the basis by which to select the descriptive labels. An intelligent way to determine which and how many terms to select is thus an interesting future extension of ICRT. This extension is of technical significance as well, as previous techniques often select cluster labels for a cluster \(c\) from main texts of articles in \(c\), by preferring those terms that are frequent in \(c\) and/or rare in all clusters [39; 40] and those terms identified by topic modeling [25]. Instead of selecting terms from the main texts, terms should be selected from IITs, as the experimental results have shown that the IITs are more effective in issue-based clustering of scholarly articles. Although these previous techniques can be used to select terms from titles of references as well, selecting terms from IITs is still a better way, as the experimental results have shown that ICRT improves clustering systems that work on titles of references (ref. those systems with 'RT' in their names in Figures 4-6). Another kind of helpful information to annotate each cluster is representative articles for the cluster, including both _citing_ and _cited_ articles. For a cluster \(c\), all articles belonging to \(c\) are candidates of _citing_ articles, as \(c\) is constructed based on the references cited by the articles. Conversely, all references cited by the articles in \(c\) are candidates of _cited_ articles. An effective way to determine which and how many articles to select is thus an interesting future extension of ICRT. It aims at selecting those articles that can indicate the research issue corresponding to \(c\), rather than those articles that are similar to other articles, which is a typical goal of previous article selection strategies. As each cluster \(c\) has a cluster IIT (i.e., \(cIIT(c)\), ref. Section 3.3), we suggest preferring those _citing_ articles whose IITs with other articles are similar to \(cIIT(c)\), as these articles should be more related to the corresponding research issue of \(c\). To select _cited_ articles for \(c\), those cited articles whose titles are similar to \(cIIT(c)\) should be preferred. Articles selected to annotate \(c\) can facilitate the navigation of the research findings related to the corresponding issue of \(c\). **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2076-3417/8/12/2591/s1](http://www.mdpi.com/2076-3417/8/12/2591/s1)]([http://www.mdpi.com/2076-3417/8/12/2591/s1](http://www.mdpi.com/2076-3417/8/12/2591/s1)), Table S1: Gold standard clusters based on chemical-gene associations; Table S2: Gold standard clusters based on chemical-disease associations; and Table S3: Gold standard clusters based on gene-disease associations. Each row in the tables provides information about a gold standard cluster (i.e., an association curated by CTD experts): first entity, second entity, and IDs of articles that belong to the cluster. Each article has two IDs: PubMed ID and PubMed Central ID, with which readers can access the article on PubMed or PubMed Central. **Author Contributions:** Conceptualization, R.-L.L. ; Data curation, C.-K.H. ; Formal analysis, R.-L.L. and C.-K.H. ; Funding acquisition, R.-L.L. ; Investigation, R.-L.L. and C.-K.H. ; Methodology, R.-L.L. and C.-K.H. ; Project administration, R.-L.L. ; Resources, R.-L.L. ; Software, C.-K.H. ; Supervision, R.-L.L. ; Validation, R.-L.L. and C.-K.H. ; Visualization, R.-L.L. and C.-K.H. ; Writing--original draft, R.-L.L. ; Writing--review & editing, R.-L.L. and C.-K.H. **Funding:** The APC was funded by Tzu Chi University, Taiwan. **Acknowledgments:** The authors are grateful to [PERSON] and [PERSON] for collecting the experimental data.