SituationSituation is another elusive concept widely used in the information-seekingliterature, but often without definition. Cool (2001) points out that there is nosingle definition of situation; a multiplicity of understanding of situation exists;situation is closely related to context; and the two terms are often usedinterchangeably in the literature although they should be differentiated. Situationis a sense of context that can impact the individual as a set of external or environ -mental factors (Johnson, 2003). However, Wersig’s (1979) problematic situationis an internal factor because the person must recognize his or her problem andsituation. B. Allen (1996) advanced the concept situation in the person-in-situation model. An in-situation can be understood as a collective situation in whichdifferent individuals face the same problems, which provides a basis for studyinginformation behavior. An in-situation may be homelessness, unemployment,health problems, collaborative projects and so on. Allen’s model brings observa -tions of information users from the individual level to a social and environmentallevel. (Although Allen did not cite Wersig’s article, a link clearly exists betweenthe problematic situation concept and the person-in-situation model.)Situation is understood as both an external construct and an internal constructwhile context is mostly an external construct. As an external construct, situationssomewhat overlap with but are also different from contextual factors, in thatsituations are much more dynamic and personal than context. Situations asperceived by the individual affect behavior at the moment of interactions aswell as across the task over time (specific, periodical or longitudinal informationneeds). As an internal construct, situational factors include a person’sknowledge of the task, perception of the task goals, mental model of informationretrieval interactions (interfaces and systems), information competency,cognitive capacity, affective state, physical condition and so on. Situation is auseful construct in understanding information behavior in general andinformation retrieval interaction in particular.