## 4 The Use of Personalized Ontologies for Re-ranking Search Results
### Approaches Defined to Re-rank the Search Results Based on the Use of Personalized Ontologies  
In [10] the authors have defined a Web system which aims to improve the quality of a user's search on the Web. The objective is obtained by personalizing a Web search according to the user's interests. The authors state that a personalized search can be of two types: _context oriented_ and _individual oriented_. In \begin{table}
\begin{tabular}{c c c} \hline
**Reference** & **Considered User’s Actions** & **Personal Ontology** \\ \hline [10, 21, 61, 62, 63] & frequency of the visits to a page, & based on the ODP \\  & time spent on a page, saving a page, _etc._ & \\ \hline [9] & past user’s queries & based on the ODP \\ [64] & selection of terms from the ODP & based on the ODP \\ [13] & past user’s queries, & based on the ODP \\  & the preferred documents and interests & \\  & explicitly declared. & \\ \hline \end{tabular}
\end{table} 
Table 2: Synthesis of the discussed methods for re-ranking of search results. the first case, the context of a search can be derived from the query terms written by a user; whereas in the second case, the context of a search is obtained by analyzing the user's behaviour during previous Web searches, e.g. actions such as saving, printing or copying full or part of the viewed pages. In the Web system developed by the authors both these types of context are taken into account to improve the quality of a search. The results obtained by the existing search engines, after the evaluation of a user's query, are collected, analyzed, re-ranked based on the user's interests, and then recommended to the users through the given user interface. In particular, in this work two types of ontologies can be used to personalize a Web search: a page ontology and a personalized ontology. Page ontology is an incremental ontology, it is constructed based on the set of pages visited by the user during his/her search session; whereas a personalized ontology is defined by considering several factors of personalization, such as page view time, actions performed on a page, terms written in previous queries, and the relevant concepts extracted from the examined Web pages. The page ontology is generated to exploit the links between the various pages visited by the user after a search session. From each visited page the relevant concepts are extracted, and they are used to represent such pages. Relations between concepts are defined with the adoption of both the ODP and a dictionary. The re-ranking process privileges the pages having the highest number of concepts related to the user's query, and where the user spent the most time. These pages will have a higher ranking position than the other ones. The personalized ontology is defined by performing a mapping between the relevant concepts extracted from the visited pages and the concepts of interest extracted from the search queries. The extracted concepts are linked in a conceptual way with the support of both the ODP and a dictionary. In particular, \(is-a\) and \(part-of\) are the relationships identified between the concepts in this step. Each node in the personalized ontology is defined by three components: a concept, the Web page(s) containing the concept, and a weight. The weight is calculated based on the actions performed by the user on this particular Web page. Each action determines the page relevance with respect to the user's context of search. For example, if \(Action=Save\) then the \(weight=1\) or if \(Action=Copy\) then weight will have a value from \(0.25\) to \(0.75\). The Protege tool can define the personalized ontology in a specific ontological language. The pages having concepts with a high weight will obtain a high position ranking. The goal of a personalized Web search is to tailor search results to the user's interests and preferences. In [21, 61, 62] a strategy to define an ontological user profile to personalize search results for a given query has been presented.