## 1 Introduction  
Search strategy is one of the major topics in interactive information retrieval (IR) studies, and many researchers have tried to identify various search strategies in the contexts of different tasks and situations. In a broad sense, a search strategy refers to a plan for a search task [1]. When users conduct information searches, they must have some search strategies that are a combination of the choice of terms, operators, and tactics [2]. Search strategies are the products of planned or situational interactions between users and IR systems. A search tactic refers to a single movement or an action to achieve specific objectives in the information searching process, while a search strategy highlights a working plan and interactive reaction for a given situation. A search strategy consists of a series of sequential tactics that take into account both planned and situational elements [3]. Our study adopts this definition of search strategy and considers sequential tactics as the major component of a search strategy.  
Search strategies in the web environment imply more possible interactions between users and IR systems than traditional searching environments. Working with web interfaces, users apply various types of tactics such as typing URLs, moving forward and backward, query formulation, scanning websites, following links, searching known addresses, saving documents, _etc._[4, 5, 6, 7]. In the web environment, users incorporate various chains of search tactics and then formulate strategies to achieve search goals or tasks efficiently and effectively. However, web IR systems do not effectively support users in applying tactics to formulate search strategies. Compared with traditional IR systems, web IR systems offer a simplified and easy environment for users that requires different types of cognitive involvement. Web IR systems here refer to any IR systems that users can access and use on the web, including but not limited to web search engines, online databases, online public access catalogs (OPACs), digital libraries, _etc._  
The IR process is complicated and dynamic, as is the application of search strategies, which consists of multiple types of search tactics. In order to understand the dynamic search strategies, researchers need to look into the sequential patterns of search tactics. In web searching, users build search strategies by selecting a series of search tactics, such as creating a query, clicking hyperlinks, and evaluating the relevance of an item. Many researchers have paid attention to identifying types of search strategies during the information searching process. However, little research has generated search strategies based on the analysis of sequential tactics applied in the web environment. Most of the prior research on search strategies focused on query-related tactics [8, 9, 10], illustrated search strategies at conceptual levels [11], or chose specific user groups, such as engineers or scientists [12].  
In order to identify types of search strategies, there is a need to explore sequential patterns of search tactics empirically by investigating real users' search behaviors in accomplishing their real tasks in the web-based search environment. This study intends to identify different types of search strategies based on the analysis of real users' sequences of search tactics in achieving their real tasks. The findings of this study help researchers better understand how users develop their search strategies. The identification of search strategies offers implications for IR system design to support different types of search strategies.