# Data Anonymization for Hiding Personal Tendency in Set-Valued Database Publication
## 1 Introduction  
Publishing a set-valued database such as a web access database brings many benefits for various applications like market analysis, advertising and recommender systems. Table 1 shows an example of such a database containing URL's of individual's web access as items. To simplify discussion, each URL is expressed by number as its ID. Releasing such a database to the public imposes some challenges since data recipients can directly associate an individual with his/her record to infer personal sensitive information such as personal preference or personal tendency. According to the Oxford on-line dictionary the term tendency refers to an inclination towards certain characteristics or type of behavior. In this context, we consider that individual tendency is an inclination of someone toward certain groups or category of items. For example, a person who accesses to some specific website such as football.com, espn.com, and livescore.com has a tendency to football. Therefore, the more someone accesses to a certain category of websites, the more obvious that the person has a tendency to the category. For some people, their personal tendency toward certain things can be considered as sensitive information and there is a trade-off for disclosing it [1]. Hiding personal tendency in a set-valued database i.e., web access log is essential for security application such as to avoid the Internet users get email spam and phishing. To illustrate the importanceof hiding personal tendency we give the following example. An internet user, [PERSON], accessed various websites where most of the websites that he visited can be categorized as automobile websites, and to this end we can say that [PERSON] has a strong tendency to the automobile category. The web address that [PERSON] accessed are collected by On-line advertisement company, says AdOn. In one day AdOn release the log of the internet users, including [PERSON]'s web access log to its collaborator company, namely AdOff. Unfortunately, an irresponsible agent who is working in AdOff knows the information about [PERSON]'s tendency by analyzing his browsing history and starts to send email spam that contains interesting information about automobiles, as well as inserting a malicious link in the email, due to his curiosity [PERSON] may get in trouble if he clicks the malicious link. The illustration story tells us that the spammer sends email spam that is precisely related to the targeted personal tendency. However, if [PERSON]'s tendency is hidden, the spammer might fail to trap [PERSON], since the email spam would not be too precise to [PERSON]'s personal tendency. As a result, even if [PERSON] receives the email he might ignore it and refrain to click a link that does not attract him. As the nature of a set-valued database where an individual is directly correlated to his/her items, accordingly, prior to publishing such a database to the public, one should consider a data anonymization process such that the personal tendency of individuals can be protected in a published database. Several data anonymization techniques such as generalization based techniques, suppression based techniques, substitution based technique and swapping based techniques have been intensively studied and each of them has pros and cons. However, there are very few researches on hiding personal tendency in set-valued database. Employing data anonymization techniques by means of a generalization based approach such as \(k\)-anonymity [2] and \(k^{m}\)-anonymity [3] cannot successfully hide personal tendency even if some items are changed to its general value. Such a failure occurs due to generalization only replaces specific item with its general value i.e., category which still pictures the tendency of an individual. For example, [PERSON] likes to access autocars.net which is categorized as an automobile website, but replacing the website name with its category i.e., automobile, it does not hide that [PERSON] has a tendency toward automobiles.