202 S Schiaffino and A. Amandi 3.1 Explicit Information The simplest way of obtaining information about users is through the data they input via forms or other user interfaces provided for this purpose. Usually, this type of information is optional since users are not willing to fill in long forms providing information about them. Generally, the information gathered in this way is demographic, such as the users age, gender, job, birthday, marital status, and hobbies. For eample, in(Adomavicius and Tuzhilin, 2001)this information consti- tutes the factual profile(name, gender, and date of birth), which is obtained by the e-commerce system from the customer's data In addition, personal interests can be informed explicitly. For example, in NewsAgent( Godoy et al, 2004) the user can indicate which sections of a digital newspaper he likes to read, which newspaper he prefers, or indicate general inter- esting topics, such as football, through a user interface, and he can also rate pages as interesting or uninteresting while he is reading. Figure 4 shows the user inter- faces for these purposes. In Syskill Webert(Pazzani et al, 1996), users make explicit relevance judgments of pages explored while browsing the Web. Syskill Webert learns a profile from the user's ratings of pages and uses this profile to suggest other pages. The user can rate a page as either hot (two thumbs up), luke warm(one thumb up and one thumb down), or cold(two thumbs down). The Apt Decision agent( Shearin and Lieberman, 2001) learns user preferences in the do- main of rental real estate by observing the users critique of apartment features Users provide a small number of criteria in the initial interaction consisting of number of bedrooms, city, and price, then receive a display of sample apartment and then react to any feature of any apartment independently, in any order Another way of providing explicit information is through the"Programming by Example"(PBE)or"Programming by Demonstration"paradigm(Lieberman, 2001b). In this approach, the user demonstrates examples to the computer. A Select Papers INCLUDE NTERNATIONAL TERRORISML Selected items Fig. 4. Providing explicit information about a users interests202 S. Schiaffino and A. Amandi 3.1 Explicit Information The simplest way of obtaining information about users is through the data they input via forms or other user interfaces provided for this purpose. Usually, this type of information is optional since users are not willing to fill in long forms providing information about them. Generally, the information gathered in this way is demographic, such as the user’s age, gender, job, birthday, marital status, and hobbies. For eample, in (Adomavicius and Tuzhilin, 2001) this information consti￾tutes the factual profile (name, gender, and date of birth), which is obtained by the e-commerce system from the customer’s data. In addition, personal interests can be informed explicitly. For example, in NewsAgent (Godoy et al, 2004) the user can indicate which sections of a digital newspaper he likes to read, which newspaper he prefers, or indicate general inter￾esting topics, such as football, through a user interface, and he can also rate pages as interesting or uninteresting while he is reading. Figure 4 shows the user inter￾faces for these purposes. In Syskill & Webert (Pazzani et al, 1996), users make explicit relevance judgments of pages explored while browsing the Web. Syskill & Webert learns a profile from the user’s ratings of pages and uses this profile to suggest other pages. The user can rate a page as either hot (two thumbs up), luke￾warm (one thumb up and one thumb down), or cold (two thumbs down). The Apt Decision agent (Shearin and Lieberman, 2001) learns user preferences in the do￾main of rental real estate by observing the user’s critique of apartment features. Users provide a small number of criteria in the initial interaction consisting of number of bedrooms, city, and price, then receive a display of sample apartments, and then react to any feature of any apartment independently, in any order. Another way of providing explicit information is through the "Programming by Example" (PBE) or "Programming by Demonstration" paradigm (Lieberman, 2001b). In this approach, the user demonstrates examples to the computer. A Fig. 4. Providing explicit information about a user’s interests