  Exploratory search starts with ill-defined goals and involves browsing,
learning, and formulating new targets for search. To fluidly support such
dynamic search behaviours, we focus on devising interactive visual facets
(IVF), visualising information facets to support user comprehension and control
of the information space. To do this, we reviewed existing faceted search
interfaces and derived two design requirements (DR) that have not been fully
addressed to support fluid interactions in exploratory search. We then
exemplified the requirements through devising an IVF tool, which coordinates a
linear and a categorical facet representing the distribution and summarisation
of items, respectively, and providing context for faceted exploration (DR1). To
support rapid transitions between search criteria (DR2), the tool introduces a
novel design concept of using facets to select items without filtering the item
space. Particularly, we propose a filter-swipe technique that enables users to
drag a categorical facet value sequentially over linear facet bars to view the
items in the intersection of the two facets along with the categorical facet
dynamically summarizing the items in the interaction. Three applications
demonstrate how the features support information discovery with ease. A user
study of 11 participants with realistic email search tasks shows that dynamic
suggestions through the timeline navigation can help discover useful
suggestions for search; the novel design concept was favoured over using facet
values as filters. Based on these practices, we derive IVF design implications
for fluid, exploratory searches.
