## 3 Results for the Research Questions
### RQ2: What Are the Expertise Sources Used for Experts Finding Systems? First, in order to decide if a person is an expert in a particular area, we need to obtain relevant information about that person; this information is called expertise sources. Expertise sources can include publications, homepages, related documents, and social networks. In this study, expertise sources in current expert finding systems have been classified into the following three channels and are represented in detail in Table 4. The table contains the three channels, the expertise sources that relate to each channel, and the previous studies that used the expertise source. 1. Textual sources--Textual sources can be considered as the main evidence of expertness. They include documents, user profiles (meta databases or homepages), and communications (e-mails and textual chats) [45]. Documents are secondary data sources that can be used as expertise evidence to automatically extract candidate experts [4]. There are different types of documents \begin{table}
\begin{tabular}{c c c c} \hline \hline
**The Domain** & **Task** & **Frequency** & **References** \\ \hline \multirow{6}{*}{Academia University} & Research collaboration & 1 & [37] \\  & Paper reviewing & 2 & [38; 39] \\  & university-industry & 1 & [25] \\  & collaboration & & \\  & Supervisor finding & 1 & [26] \\  & Similar researcher & 2 & [27; 40] \\  & No specific task & 6 & [41; 42; 43; 44; 45; 46] \\  & Research collaboration & 12 & [20; 21; 47; 48; 49; 50; 51; 52; 53; 54; 55] \\  & Paper reviewing & 7 & [5; 56; 57; 58; 59; 60] \\ \multirow{2}{*}{Academia Social Network} & Finding group of experts & 3 & [61; 62; 63] \\  & R\&D & 2 & [64; 65] \\  & No specific task & 8 & [66; 67; 68; 69; 70; 71; 72; 73] \\ \multirow{2}{*}{Enterprise} & & 10 & [15; 22; 35; 36; 74; 75; 76; 77; 78; 79] \\  & Medicine & 2 & [80; 81] \\ Knowledge Sharing Communities & & 6 & [16; 17; 19; 44; 82; 83] \\ \multirow{2}{*}{Online forums} & & 2 & [84; 85] \\  & Social network & 4 & [56; 57; 86; 87; 88] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Expert finding systems’ domains. that have been used in the current expert finding systems studies. The most used textual expertise source is publications, which have been used by authors in [36; 38; 44; 48; 49; 53; 58; 59; 61; 62; 66; 67; 68; 70; 71; 73; 74; 75; 76; 77; 78; 79; 80] as their main expertise source, while publications have been combined with other expertise sources in [22; 40; 41; 43; 44; 47; 55; 60; 69; 75; 88; 89]. In addition to publications, reference [42] used movies as expertise evidence. Two studies [80; 81] used medical documents. Moreover, another two studies [15; 77] used employee documents. Also, a bug repository was used as expertise evidence by the authors in reference [36]. Reference [78] used enterprise terminologies in their system as expertise evidence, while reference [79] used transactional data. Additionally, relevance feedback and log repository have been used by authors in reference [74] and reference [35], respectively. The advantage of using documents as expertise sources is the simplicity of extracting up-to-date information about a particular expert. However, their disadvantage is that they cannot contain all the required information. For example, it is difficult to discover junior experts who have no publications. Meta databases are the main store of employees' expertise in organizations. They are used to store personal profiles for employees [4]. For example, a university expertise database saves the profiles of university members with all academic information including personal information, research students, expertise areas, projects, and publications. Among many different expertise sources, faculty and university personal homepages are a valuable and reliable source, since they usually contain relatively well-formatted data [31]. The authors of references [5; 26; 27; 44] used homepages as expertise evidences for their systems.