Search engines such as Google, Bing, and Yahoo, supplemented by other information search portals like Wikipedia, have become the means for searching information on the Internet. Along with the increasing popularity of search engines, the academic interest in search has shifted from analysing simple look-up query and response patterns to analysing rather complex information seeking needs. Current search tools seem to support complex search not as well as they do in the case of look-up. Especially support for aggregating search results from multiple search-queries, taking into account discoveries made during a complex search task, and synthesizing them to some newly compiled document of information is only at the beginning and motivates researchers to develop new tools for supporting those information seeking techniques. We focus in this work on the exploratory search concepts aggregation, discovery, and synthesis. Our idea is that these are today the most time consuming activities, especially when fulfilling a complex information need. We will use these three concepts throughout this paper to evaluate different approaches in exploratory search and give an overview of the state of the art and current ongoing research in respect to these concepts.
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