Yi-Shin Chen and Cyrus Shahabi according to the survival ability for reproducing offspring. The offspring are generated through crossover and mutation processes and are used for replac ing some chromosomes in the population with a probability consistent with their fitness values. In other words, with the help of the fitness function te point out the correct direction, GA could construct better and bet ter chromo somes from the best partial genes of past samplings. Please see reference [17 for mathematical foundati n summary, Ga is composed of a fitness function, a population of chromo somes and three operators-selection, crossover and mutation. The parameter settings of the operators can be chosen depending on the applications or re ain unchanged even when the applications are varied. However, the fitness function and the coding met hod are required to be specially designed for each problem. The design of fitness function and encoding method for Yoda will 3 Overview The primary objective of a web-based recommendation system can be stated Problem 1. Suppose the item-set I= ii is an item presented in a web-site f and u is a user interactively navigating the Web-site. The recommendation problem is to obtain the wish-list lu e l, which is a list of items that are ranked based on u's interests In general, to acquire a wish-list for a user, a recommendation process goe through three steps/phases 1. Obtaining User Perceptions: Data about user perceptions such as naviga tion behaviors are collected. In some systems 8.7, these data need further processing for abstracting data which are used in the later phases 2. Ranking the Items: The predicted user interests are utilized to provide the predicted user wish-list 3. Adjusting user settings: The system acquires relevance feedback (or follow-up navigation behaviors)from the user and employs it to refine the user set tings/profiles, which represent the user perceptions On occa sion, this phase is integrated into phase one. Figure 1 illustrates the processing flow of Yoda. Suppose that music Cds are the items presented in a web-site. Yoda provides each active user a list of ecommended CDs by analyzing his/her navigation behaviors. To generate the recommendations, during an offline process, Yoda obtains experts'recom mendation(termed erperts'wish-Iists ) which could be from human experts, clusters of user evaluations, or clusters of navigation patterns. Later, dur ng the on- line recommendation process, the system first acquires the initial user profile, which is composed of a list of confidence values and a fuzzy❼ ➳✸❵ ❸❡❜✦✇♥❵❚①❤✕✇♥❳✽❚✵❬✍❚❉❪①❤✈❝✦❩❇♠♥❞❍❜✦✇❉❬✍✇❉❬✍➝♥❵ ❏❛➮✍➮✣➱❛◆✽❑⑧❃❋❊Ð✮❒P➱✵❒P❈❊■✛◗❭❖❊◆PÒ❉❃Ò❲❏✦Ï✈❏✦❘❊❃ Ï ❃❒❇▼➢❮➊➱❛◆✖◆P■✍ß❊◆P➱⑧❑⑧❖▲➮✣❃❋❊Ð✵➱✦â❁◗❭ß❊◆P❃❋❊Ð▲ä❊æ✸❈❊■❣➱✦â❁◗❭ß❊◆P❃❋❊Ð➢❏✦◆P■ Ð❛■✍❋❊■✍◆✽❏❲❒P■❦❑✮❒P❈❊◆P➱❛❖❊Ð❛❈➧➮✣◆P➱♥◗P◗❭➱❲Ò❛■✍◆✼❏✦❋▲❑①✃✧❖⑧❒✽❏❲❒P❃➱❛❋➢ß❊◆P➱⑧➮✣■❦◗P◗❭■❦◗❍❏✦❋▲❑➧❏✦◆P■✖❖▲◗❭■❦❑✵❮➊➱❛◆✐◆P■✍ß❊Ï④❏❛➮❫❅ ❃❋❊Ð☞◗❭➱❛✃✵■✧➮✽❈❊◆P➱❛✃✵➱♥◗❭➱❛✃✵■❦◗✱❃❋✿❒P❈❊■✧ß➩➱❛ß❊❖❊Ï④❏❲❒P❃➱❛❋åç✱❃❒P❈á❏①ß❊◆P➱❛❘▲❏✦❘❊❃ Ï ❃❒❇▼✝➮✣➱❛❋▲◗❭❃④◗❇❒P■✍❋♥❒✡ç✱❃❒P❈ ❒P❈❊■✍❃ ◆✭￾❊❒P❋❊■❦◗P◗➽Ò❲❏✦Ï❖❊■❦◗✍ä➤èq❋á➱✦❒P❈❊■✍◆➽ç✐➱❛◆✽❑❊◗✍❐➤ç✱❃❒P❈✢❒P❈❊■①❈❊■✍Ïßá➱✦❮❍❒P❈❊■✻￾❊❒P❋❊■❦◗P◗❄❮➊❖❊❋▲➮❫❒P❃➱❛❋✢❒P➱ ß➩➱❛❃❋♥❒②➱❛❖⑧❒✈❒P❈❊■✸➮✣➱❛◆P◆P■❦➮❫❒✈❑⑧❃ ◆P■❦➮❫❒P❃➱❛❋✂❐✞✮Þ ➮✣➱❛❖❊Ï④❑✛➮✣➱❛❋▲◗❇❒P◆P❖▲➮❫❒✕❘➩■✣❒❭❒P■✍◆✟❏✦❋▲❑❣❘➩■✣❒❭❒P■✍◆✟➮✽❈❊◆P➱❛✃✵➱✦❅ ◗❭➱❛✃✵■❦◗✟❮➊◆P➱❛✃➫❒P❈❊■✡❘➩■❦◗❇❒✐ß▲❏✦◆❭❒P❃④❏✦Ï▲Ð❛■✍❋❊■❦◗✼➱✦❮✂ß▲❏❛◗❇❒✸◗P❏✦✃✵ß❊Ï ❃❋❊Ð♥◗✍ä✁￾✼Ï■❦❏❛◗❭■✖◗❭■✍■✡◆P■✣❮➊■✍◆P■✍❋▲➮✣■★✯ ✱✞❪✶✸ ❮➊➱❛◆✱✃①❏❲❒P❈❊■✍✃①❏❲❒P❃④➮✍❏✦Ï➤❮➊➱❛❖❊❋▲❑❊❏❲❒P❃➱❛❋▲◗✍ä èq❋✛◗❭❖❊✃✵✃①❏✦◆P▼❛❐✶✮Þ ❃④◗✈➮✣➱❛✃✵ß➩➱♥◗❭■❦❑➽➱✦❮⑧❏ ￾❊❒P❋❊■❦◗P◗❁❮➊❖❊❋▲➮❫❒P❃➱❛❋✂❐t❏✸ß➩➱❛ß❊❖❊Ï④❏❲❒P❃➱❛❋❣➱✦❮❊➮✽❈❊◆P➱❛✃✵➱✦❅ ◗❭➱❛✃✵■❦◗✕❏✦❋▲❑➽❒P❈❊◆P■✍■✐➱❛ß➩■✍◆✽❏❲❒P➱❛◆✽◗➤❅❁◗❭■✍Ï■❦➮❫❒P❃➱❛❋✂❐❲➮✣◆P➱♥◗P◗❭➱❲Ò❛■✍◆✂❏✦❋▲❑❣✃✧❖⑧❒✽❏❲❒P❃➱❛❋✂ä❲æ✸❈❊■❍ß▲❏✦◆✽❏✦✃✵■✣❒P■✍◆ ◗❭■✣❒❭❒P❃❋❊Ð♥◗✱➱✦❮✕❒P❈❊■❣➱❛ß➩■✍◆✽❏❲❒P➱❛◆✽◗✸➮✍❏✦❋✝❘➩■✛➮✽❈❊➱♥◗❭■✍❋✝❑⑧■✍ß➩■✍❋▲❑⑧❃❋❊Ð①➱❛❋☞❒P❈❊■✧❏✦ß❊ß❊Ï ❃④➮✍❏❲❒P❃➱❛❋▲◗✸➱❛◆✱◆P■✣❅ ✃①❏✦❃❋☞❖❊❋▲➮✽❈▲❏✦❋❊Ð❛■❦❑➧■✍Ò❛■✍❋➧ç✱❈❊■✍❋☞❒P❈❊■✛❏✦ß❊ß❊Ï ❃④➮✍❏❲❒P❃➱❛❋▲◗✸❏✦◆P■❄Ò❲❏✦◆P❃■❦❑❁ä❋✦✖➱❲ç✐■✍Ò❛■✍◆❦❐❛❒P❈❊■✭￾❊❒P❋❊■❦◗P◗ ❮➊❖❊❋▲➮❫❒P❃➱❛❋✵❏✦❋▲❑✛❒P❈❊■✱➮✣➱⑧❑⑧❃❋❊Ð❄✃✵■✣❒P❈❊➱⑧❑✮❏✦◆P■❍◆P■❦Ñ♥❖❊❃ ◆P■❦❑❣❒P➱❄❘➩■✱◗❭ß➩■❦➮✣❃④❏✦Ï Ï▼✧❑⑧■❦◗❭❃Ð❛❋❊■❦❑❣❮➊➱❛◆②■❦❏❛➮✽❈ ß❊◆P➱❛❘❊Ï■✍✃✝ä➤æ✸❈❊■✵❑⑧■❦◗❭❃Ð❛❋✢➱✦❮✑￾❊❒P❋❊■❦◗P◗✡❮➊❖❊❋▲➮❫❒P❃➱❛❋á❏✦❋▲❑å■✍❋▲➮✣➱⑧❑⑧❃❋❊Ð➧✃✵■✣❒P❈❊➱⑧❑å❮➊➱❛◆✡❂✼➱⑧❑❊❏➧ç✱❃ Ï Ï ❘➩■✛❑⑧■❦◗P➮✣◆P❃❘➩■❦❑➧❃❋å❆❉■❦➮❫❒P❃➱❛❋ ✲▲ä ❚❊ä ✂ ✄✆☎☎✂Ø✝☎✖Ý☛☎✟✞ æ✸❈❊■✡ß❊◆P❃✃①❏✦◆P▼✧➱❛❘❆❅❇■❦➮❫❒P❃Ò❛■✖➱✦❮✈❏❣ç✐■✍❘⑧❅❡❘▲❏❛◗❭■❦❑✵◆P■❦➮✣➱❛✃✵✃✵■✍❋▲❑❊❏❲❒P❃➱❛❋①◗❭▼⑧◗❇❒P■✍✃ ➮✍❏✦❋①❘➩■❄◗❇❒✽❏❲❒P■❦❑ ❏❛◗✐❮➊➱❛Ï Ï➱❲ç✖◗✄✂ ✠✐òPï❛õ✟✏ ñ✣ð☛✡✌☞✡❆❉❖❊ß❊ß➩➱♥◗❭■❣❒P❈❊■ ✒➀îqñ✣ð✻✠❡í✍ñ✣î✎✍✑✏✓✒✕✔✗✖ ✔❍❃④◗✡❏✦❋✝❃❒P■✍✃✥ß❊◆P■❦◗❭■✍❋♥❒P■❦❑☞❃❋å❏✵ç✐■✍❘⑧❅q◗❭❃❒P■ ✘ ❏✦❋▲❑✑✙☞❃④◗❍❏✛❖▲◗❭■✍◆❍❃❋♥❒P■✍◆✽❏❛➮❫❒P❃Ò❛■✍Ï▼✮❋▲❏tÒ❉❃Ð♥❏❲❒P❃❋❊Ð➽❒P❈❊■✡ûá■✍❘⑧❅q◗❭❃❒P■❛ä❉æ✸❈❊■✡◆P■❦➮✣➱❛✃✵✃✵■✍❋▲❑❊❏❲❒P❃➱❛❋ ß❊◆P➱❛❘❊Ï■✍✃✓❃④◗❣❒P➱å➱❛❘⑧❒✽❏✦❃❋á❒P❈❊■✢ó❁✒④íPô✙✠✼✏✒④í❫î✚✍✗✛✢✜✣✍▲❐✈ç✱❈❊❃④➮✽❈à❃④◗✧❏✿Ï ❃④◗❇❒✧➱✦❮✱❃❒P■✍✃①◗✛❒P❈▲❏❲❒✮❏✦◆P■ ◆✽❏✦❋❊Ó❛■❦❑➢❘▲❏❛◗❭■❦❑➧➱❛❋✤✙✕ü ◗✸❃❋♥❒P■✍◆P■❦◗❇❒✽◗✍ä èq❋åÐ❛■✍❋❊■✍◆✽❏✦Ï❯❐❊❒P➱➧❏❛➮✍Ñ♥❖❊❃ ◆P■✧❏①ç✱❃④◗❭❈⑧❅❡Ï ❃④◗❇❒✡❮➊➱❛◆❄❏➢❖▲◗❭■✍◆❦❐➩❏①◆P■❦➮✣➱❛✃✵✃✵■✍❋▲❑❊❏❲❒P❃➱❛❋✿ß❊◆P➱⑧➮✣■❦◗P◗✖Ð❛➱❉■❦◗ ❒P❈❊◆P➱❛❖❊Ð❛❈➧❒P❈❊◆P■✍■❣◗❇❒P■✍ß▲◗✦✥tß❊❈▲❏❛◗❭■❦◗✄✂ ✱❛ä ✺❘⑧❒✽❏✦❃❋❊❃❋❊Ð★✧✡◗❭■✍◆✩￾②■✍◆✽➮✣■✍ß⑧❒P❃➱❛❋▲◗✄✂❄✹❄❏❲❒✽❏✡❏✦❘➩➱❛❖⑧❒②❖▲◗❭■✍◆✈ß➩■✍◆✽➮✣■✍ß⑧❒P❃➱❛❋▲◗✕◗❭❖▲➮✽❈✧❏❛◗✈❋▲❏tÒ❉❃Ð♥❏❲❅ ❒P❃➱❛❋❣❘➩■✍❈▲❏tÒ❉❃➱❛◆✽◗✂❏✦◆P■✼➮✣➱❛Ï Ï■❦➮❫❒P■❦❑❁ä✍èq❋✛◗❭➱❛✃✵■❍◗❭▼⑧◗❇❒P■✍✃①◗✑✯❱❊❐ ❪✶✸❡❐✣❒P❈❊■❦◗❭■❍❑❊❏❲❒✽❏✱❋❊■✍■❦❑❄❮➊❖❊◆❭❒P❈❊■✍◆ ß❊◆P➱⑧➮✣■❦◗P◗❭❃❋❊Ð✧❮➊➱❛◆✖❏✦❘▲◗❇❒P◆✽❏❛➮❫❒P❃❋❊Ð①❑❊❏❲❒✽❏✮ç✱❈❊❃④➮✽❈✝❏✦◆P■➽❖▲◗❭■❦❑➧❃❋☞❒P❈❊■❣Ï④❏❲❒P■✍◆✱ß❊❈▲❏❛◗❭■❦◗✍ä ✷⑧ä✎✪✖❏✦❋❊Ó❉❃❋❊Ð✮❒P❈❊■➽è❡❒P■✍✃①◗✄✂✻æ✸❈❊■➽ß❊◆P■❦❑⑧❃④➮❫❒P■❦❑➧❖▲◗❭■✍◆✱❃❋♥❒P■✍◆P■❦◗❇❒✽◗✱❏✦◆P■❄❖⑧❒P❃ Ï ❃❰✍■❦❑➧❒P➱✵ß❊◆P➱❲Ò❉❃④❑⑧■ ❒P❈❊■❣ß❊◆P■❦❑⑧❃④➮❫❒P■❦❑☞❖▲◗❭■✍◆✱ç✱❃④◗❭❈⑧❅❡Ï ❃④◗❇❒❦ä ❚❊ä Þ❑✤❅❇❖▲◗❇❒P❃❋❊Ð ❖▲◗❭■✍◆å◗❭■✣❒❭❒P❃❋❊Ð♥◗✄✂ æ✸❈❊■ ◗❭▼⑧◗❇❒P■✍✃✑❏❛➮✍Ñ♥❖❊❃ ◆P■❦◗☞◆P■✍Ï■✍Ò❲❏✦❋▲➮✣■á❮➊■✍■❦❑⑧❘▲❏❛➮✽Ó ✜➊➱❛◆ ❮➊➱❛Ï Ï➱❲ç✸❅❡❖❊ßà❋▲❏tÒ❉❃Ð♥❏❲❒P❃➱❛❋à❘➩■✍❈▲❏tÒ❉❃➱❛◆✽◗☞✣✡❮➊◆P➱❛✃✓❒P❈❊■➧❖▲◗❭■✍◆✵❏✦❋▲❑à■✍✃✵ß❊Ï➱❲▼⑧◗✛❃❒✧❒P➱✢◆P■✟￾▲❋❊■ ❒P❈❊■✡❖▲◗❭■✍◆✐◗❭■✣❒❭❒P❃❋❊Ð♥◗✦✥tß❊◆P➱✥￾▲Ï■❦◗✍❐❲ç✱❈❊❃④➮✽❈①◆P■✍ß❊◆P■❦◗❭■✍❋♥❒✼❒P❈❊■✖❖▲◗❭■✍◆❍ß➩■✍◆✽➮✣■✍ß⑧❒P❃➱❛❋▲◗✍ä ✺❋①➱⑧➮✍➮✍❏❲❅ ◗❭❃➱❛❋✂❐❉❒P❈❊❃④◗✱ß❊❈▲❏❛◗❭■➽❃④◗✱❃❋♥❒P■✍Ð❛◆✽❏❲❒P■❦❑➢❃❋♥❒P➱①ß❊❈▲❏❛◗❭■➽➱❛❋❊■❛ä ❃✕❃Ð❛❖❊◆P■★✱✡❃ Ï Ï❖▲◗❇❒P◆✽❏❲❒P■❦◗❍❒P❈❊■❄ß❊◆P➱⑧➮✣■❦◗P◗❭❃❋❊Ð✬✫▲➱❲ç✫➱✦❮✂❂✼➱⑧❑❊❏❊ä❊❆❉❖❊ß❊ß➩➱♥◗❭■✡❒P❈▲❏❲❒✸✃✧❖▲◗❭❃④➮❣●❄✹❄◗ ❏✦◆P■✱❒P❈❊■✡❃❒P■✍✃①◗✼ß❊◆P■❦◗❭■✍❋♥❒P■❦❑✵❃❋➧❏✛ç✐■✍❘⑧❅q◗❭❃❒P■❛ä✦❂✼➱⑧❑❊❏❣ß❊◆P➱❲Ò❉❃④❑⑧■❦◗✟■❦❏❛➮✽❈➢❏❛➮❫❒P❃Ò❛■✖❖▲◗❭■✍◆✐❏❣Ï ❃④◗❇❒✐➱✦❮ ◆P■❦➮✣➱❛✃✵✃✵■✍❋▲❑⑧■❦❑➯●❄✹❄◗✛❘❉▼ ❏✦❋▲❏✦Ï▼❉❰✍❃❋❊Ð✿❈❊❃④◗✦✥t❈❊■✍◆✛❋▲❏tÒ❉❃Ð♥❏❲❒P❃➱❛❋ ❘➩■✍❈▲❏tÒ❉❃➱❛◆✽◗✍ä✂æ✈➱åÐ❛■✍❋❊■✍◆✽❏❲❒P■ ❒P❈❊■✐◆P■❦➮✣➱❛✃✵✃✵■✍❋▲❑❊❏❲❒P❃➱❛❋▲◗✍❐❦❑⑧❖❊◆P❃❋❊Ð➽❏✦❋✛➱✥❜①❃❋❊■✐ß❊◆P➱⑧➮✣■❦◗P◗✍❐✣❂✼➱⑧❑❊❏✡➱❛❘⑧❒✽❏✦❃❋▲◗✈■✣é⑧ß➩■✍◆❭❒✽◗✍ü❦◆P■❦➮✣➱❛✃✮❅ ✃✵■✍❋▲❑❊❏❲❒P❃➱❛❋❵✜➀❒P■✍◆P✃✵■❦❑ ñ✮✭✓✽▲ñ✣ò❫î❾í✰✯♥ó❁✒④íPô✙✠✼✏✒④í❫î❾í✣❫❐❊ç✱❈❊❃④➮✽❈✝➮✣➱❛❖❊Ï④❑➧❘➩■❄❮➊◆P➱❛✃ ❈❉❖❊✃①❏✦❋☞■✣é⑧ß➩■✍◆❭❒✽◗✍❐ ➮✣Ï❖▲◗❇❒P■✍◆✽◗✧➱✦❮❄❖▲◗❭■✍◆✮■✍Ò❲❏✦Ï❖▲❏❲❒P❃➱❛❋▲◗✍❐✕➱❛◆✵➮✣Ï❖▲◗❇❒P■✍◆✽◗✮➱✦❮✡❋▲❏tÒ❉❃Ð♥❏❲❒P❃➱❛❋àß▲❏❲❒❭❒P■✍◆P❋▲◗✍ä✲✱✈❏❲❒P■✍◆❦❐②❑⑧❖❊◆❭❅ ❃❋❊Ð✵❒P❈❊■❣➱❛❋⑧❅❡Ï ❃❋❊■❣◆P■❦➮✣➱❛✃✵✃✵■✍❋▲❑❊❏❲❒P❃➱❛❋☞ß❊◆P➱⑧➮✣■❦◗P◗✍❐❉❒P❈❊■✛◗❭▼⑧◗❇❒P■✍✃ ￾▲◆✽◗❇❒✡❏❛➮✍Ñ♥❖❊❃ ◆P■❦◗❍❒P❈❊■✛❃❋❊❃❒P❃④❏✦Ï ❖▲◗❭■✍◆➢ß❊◆P➱✥￾▲Ï■❛❐✼ç✱❈❊❃④➮✽❈✫❃④◗➢➮✣➱❛✃✵ß➩➱♥◗❭■❦❑ö➱✦❮✛❏ Ï ❃④◗❇❒➧➱✦❮❣➮✣➱❛❋❆￾➩❑⑧■✍❋▲➮✣■åÒ❲❏✦Ï❖❊■❦◗➢❏✦❋▲❑⑩❏ ❮➊❖❊❰✍❰✍▼