## 2 Use of Ontologies to Capture the Information Behaviour
The approaches proposed in the literature address the definition of methodologies to identify the useful information in the ontology to improve a search task [6, 23]. Two main approaches have been investigated: query expansion, and re-ranking of the results produced by a search engine in response to a user's query. In query expansion a personal ontology can be used to automatically expand the user's search, in order to contextualize it. Whereas in the re-ranking phase, a personal ontology can be used to re-rank the search result based on the conceptual schema provided by the user ontology structure. In the literature, hybrid approaches are also proposed. In [24] a survey of methodologies of  
Figure 1: A simple example of an ontological user profile. concept-based query expansion for re-ranking multimedia documents is reported. The query expansion process (especially for short query) can improve recall, whereas the re-ranking phase can improve precision; thus techniques based on hybrid methodologies are preferred [24]. In Section 3 an overview of some works presented in the literature concerning the use of a personalized ontology aimed at query expansion is reviewed; in Section 4 an overview of some strategies defined in the literature employed for re-ranking search results according to the user interests is presented. **The Open Directory Project** As previously outlined, an ontological user profile is essentially a portion of a reference knowledge, where each concept refers to the user's perceived interest. In this short review of ontology-based approaches to personalization, the Open Directory Project (ODP) is the reference knowledge adopted by most research works that will be reported in Section 3 and 4 The ODP, also known as Dmoz, is a multilingual open content directory of World Wide Web links. The ODP was founded in the United States as Gnuhoo by [PERSON] and [PERSON] in 1998 while they were both working as engineers for Sun Microsystems. It is now owned by Netscape, but it is maintained by a community of volunteer editors. The ODP uses a hierarchical ontology scheme for organizing web-sites listings. Listings on a similar topic are grouped into categories, arranged by subject (from broad to specific). Here below a small portion of categories listing obtained by the ODP archive (on date: 2010-05-11) is shown. _Adult_  
_Adult/Arts_  
_Adult/Arts/Animation_  
_Adult/Arts/Animation/Anime_  
_Adult/Arts/Animation/Anime/Fan_Works_  
_Adult/Arts/Animation/Anime/Fan_Works/Fan_Art_  
_Adult/Arts/Animation/Anime/Fan_Works/Fan_Fiction_  
_Adult/Arts/Animation/Anime/Games/Companies_  
_Adult/Arts/Animation/Anime/Games/Reviews_  
_Adult/Arts/Animation/Anime/Gennes_  
...  
To keep the ODP running smoothly, some set up policies for submitting sites are stated. Submissions that violate these policies are rejected. Furthermore, the ODP data are made available through a non standard RDF format. One strategy that allows to define a user profile is to automatically extract the relevant concepts from the preferred user's Web pages. _The ODP is the largest, most comprehensive human-edited directory of the Web_, thus many researchers have used it for their research activities.