Collaboration partners do so by providing query terms, collective tagging, adding comments or opinions, rating search results, and links clicked of former (successful) IR activities to users having the same or a related information need.
Collaborative search engines can be classified along several dimensions: intent (explicit and implicit) and synchronization,[1] depth of mediation,[2] task vs. trait,[3] division of labor, and sharing of knowledge.
I-Spy,[5] Jumper 2.0, Seeks, the Community Search Assistant,[6] the CSE of Burghardt et al.,[7] and the works of Longo et al. [8] [9] [10] all represent examples of implicit collaboration.
PlayByPlay[12] takes a step further to support general purpose collaborative browsing tasks with an instant messaging functionality.
However, in Papagelis et al.[14] terms are used differently: they combine explicitly shared links and implicitly collected browsing histories of users to a hybrid CSE.
PlayByPlay[12] is another example of UI-level mediation where all users have full and equal access to the instant messaging functionality without the system's coordination.
This model classifies people's membership in groups based on the task at hand vs. long-term interests; these may be correlated with explicit and implicit collaboration.
CoSearch[20] is a system that supports co-located collaborative web search by leveraging extra mobile phones and mice.
Search terms and links clicked that are shared among users reveal their interests, habits, social relations and intentions.
(Note, even when explicitly sharing queries and links clicked, the whole (former) log is disclosed to any user that joins a search session).