In order to design successful search user interfaces, it is necessary to understand the human information seeking process, including the strategies people employ when engaged in search. Numerous theoretical treatments have been proposed to characterize this complex cognitive process (Belkin et al. 1982; Jarvelin and Ingwersen 2004; Kuhlthau 1991; Marchionini 1995; Saracevic 1997; Sutcliffe and Ennis's 1998). This chapter presents the most commonly discussed theoretical models of the search process: the standard model, the cognitive model, the dynamic model, search as a sequence of stages, search as a strategic process, and sensemaking. The chapter concludes with a discussion of information needs, including methods for inferring information needs from their expression as queries.

The Standard Model of Information Seeking

Many accounts of the information seeking process assume an interaction cycle consisting of identifying an information need, followed by the activities of query specification, examination of retrieval results, and if needed, reformulation of the query, repeating the cycle until a satisfactory result set is found (Salton 1989; Shneiderman et al. 1998). As Marchionini (1989) puts it:

This model is elaborated by Sutcliffe and Ennis's (1998) oft-cited information seeking process model, which they formulate as a cycle consisting of four main activities:

• Problem identification,

• Articulation of information need(s),

• Query formulation, and

• Results evaluation.