The Research on Recommender for New Customers Using Collaborative Filtering and Social Network Analysis (협력필터링과 사회연결망을 이용한 신규고객 추천방법에 대한 연구)
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- Journal of Intelligence and Information Systems
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- v.18 no.4
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- pp.19-42
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- 2012
Consumer consumption patterns are shifting rapidly as buyers migrate from offline markets to e-commerce routes, such as shopping channels on TV and internet shopping malls. In the offline markets consumers go shopping, see the shopping items, and choose from them. Recently consumers tend towards buying at shopping sites free from time and place. However, as e-commerce markets continue to expand, customers are complaining that it is becoming a bigger hassle to shop online. In the online shopping, shoppers have very limited information on the products. The delivered products can be different from what they have wanted. This case results to purchase cancellation. Because these things happen frequently, they are likely to refer to the consumer reviews and companies should be concerned about consumer's voice. E-commerce is a very important marketing tool for suppliers. It can recommend products to customers and connect them directly with suppliers with just a click of a button. The recommender system is being studied in various ways. Some of the more prominent ones include recommendation based on best-seller and demographics, contents filtering, and collaborative filtering. However, these systems all share two weaknesses : they cannot recommend products to consumers on a personal level, and they cannot recommend products to new consumers with no buying history. To fix these problems, we can use the information which has been collected from the questionnaires about their demographics and preference ratings. But, consumers feel these questionnaires are a burden and are unlikely to provide correct information. This study investigates combining collaborative filtering with the centrality of social network analysis. This centrality measure provides the information to infer the preference of new consumers from the shopping history of existing and previous ones. While the past researches had focused on the existing consumers with similar shopping patterns, this study tried to improve the accuracy of recommendation with all shopping information, which included not only similar shopping patterns but also dissimilar ones. Data used in this study, Movie Lens' data, was made by Group Lens research Project Team at University of Minnesota to recommend movies with a collaborative filtering technique. This data was built from the questionnaires of 943 respondents which gave the information on the preference ratings on 1,684 movies. Total data of 100,000 was organized by time, with initial data of 50,000 being existing customers and the latter 50,000 being new customers. The proposed recommender system consists of three systems : [+] group recommender system, [-] group recommender system, and integrated recommender system. [+] group recommender system looks at customers with similar buying patterns as 'neighbors', whereas [-] group recommender system looks at customers with opposite buying patterns as 'contraries'. Integrated recommender system uses both of the aforementioned recommender systems to recommend movies that both recommender systems pick. The study of three systems allows us to find the most suitable recommender system that will optimize accuracy and customer satisfaction. Our analysis showed that integrated recommender system is the best solution among the three systems studied, followed by [-] group recommended system and [+] group recommender system. This result conforms to the intuition that the accuracy of recommendation can be improved using all the relevant information. We provided contour maps and graphs to easily compare the accuracy of each recommender system. Although we saw improvement on accuracy with the integrated recommender system, we must remember that this research is based on static data with no live customers. In other words, consumers did not see the movies actually recommended from the system. Also, this recommendation system may not work well with products other than movies. Thus, it is important to note that recommendation systems need particular calibration for specific product/customer types.
To provide better health care services to the rural population, the government has made the Community Health Practitioner(CHP) a regular government official from April 1, 1992. This study was carried out to study the impact of officialization of CHP on the activities and management system of Primary Health Post(PHP). Fifty PHPs were selected by two stage sampling, cluster and simple random, from 595 PHPs in Kyungnam and Kyungpook provinces. Data were collected by a personal interview with CHPs and review of records and reports kept in the PHPs. The study was done for the periods of January 1-March 31, 1992 (before officialization) and January 1-March 31, 1993 (after officialization). Ninety-six percent of the CHPs wanted to become a regular government official in the hope of better job security and higher salary. The proportion of CHPs who were proud of their iob was increased from 24% to 46% after officialization. Those CHPs who felt insecure for their job decreased from 30% to 10%. Monthly salary was increased by 34% from 802,600 Won to 1,076,000 Won and 90% of the CHPs were satisfied with their salary, also more CHPs responded that they have autonomy in their work planning, implementation of plan, management of the post, and evaluation of their activity. There were no appreciable changes in such CHPs' activities as assessment of local health resources, drawing map for the catchment area, utilization of community organization, grasping the current population structure in the catchment area, keeping the family health records, individual and group health education, and school health service. However, the number of home visits was increased from 13.6 times on the average per month per CHP to 27.5 times. More mothers and children were referred to other medical facilities for the immunization and family planning services. Average number of patients of hypertension, cancer, and diabetes in three months period was decreased from 12.7 to 11.6, from 1.5 to 1.2, and 4.3 to 3.4, respectively. Records for the patient care, drug management, and equipment were well kept but not for other records. The level of record keeping was not changed after officialization. The proportion of PHPs which had support from the health center was increased for drug supply from 14.0% to 30.0%, for consumable commodities from 22.0% to 52.0%, for maintenance of PHP from 54.0% to 68.0%, for supply of health education materials from 34.0% to 44.0%, and supply of equipment from 54.0% to 58.0%. Total monthly revenue of a PHP was increased by about 50,000 Won; increased by 22,000 Won in patient care and 34,700 Won in the government subsidy but decreased in the membership due and donation. However, there was no remarkable changes in the expenditure. The proportion of PHPs which had received official notes from the health center for the purpose of guidance and supervision of the CHPs was increased from 20% to 38% during three months period and the average number of telephone call for supervision from the health center per PHP was increased from 1.8 to 2.1 times(p<0.01). However, the proportion of PHPs that had supervisory visit and conference was reduced from 79% to 62%, and from 88% to 74%, respectively. The proportion of CHPs who maintained a cooperative relationship with Myun Health Workers was reduced from 42% to 36%, that with the director of health center from 46% to 24%, that with the chief of public health administration section from 56% to 36%, and that with the chairman of PHP management council from 62% to 38%. Most of the CHPs (92% before and 82% after officialization) stated that the PHP management council is not helpful for the PHP. CHPs who considered the PHP management council unnecessary increased from 4% to 16%(p<0.05). Suggestions made by the CHPs for the improvement of CHP program included emphasis on health education, assurance of autonomy for PHP management, increase of the kind of drugs that can be dispensed by CHPs, and appointment of an experienced CHP in the health center as the supervisor of CHPs. The results of this study revealed that the role and function of CHPs as reflected in their activities have not been changed after officialization. However, satisfaction in job security and salary was improved as well as the autonomy. Support of health center to the PHP was improved but more official notes were sent to the PHPs which required the CHPs more paper works. Number of telephone calls for supervision was increased but there was little administrative and technical guidance for the CHP activities.
We investigated what factors motivate gamers to participate in a guild and why they continue to be engaged as members of the guild. We find that, based on the result of focus group interviews with MMORPG gamers, social support and self-esteem factors play important roles. Considering both prior research and the focus group interviews we have conducted, we define social support and character control as independent variables. Character identity, guild identity, and self-esteem are proposed as mediating variables while guild flow and game loyalty as dependent variables. Accordingly, we develop the research model and hypotheses, and verify them empirically. Based on our experiences of playing the WoW game, we proposed a research model and conducted focus-group interviews (FGIs). FGIs involve formulating a hypothesis and then collecting some relevant data. FGIs were conducted face-to-face with students of C University in Korea. We formulated structured interview schedules, and the questions were based on our research variables and personal experiences. The questions for the interviews encompassed the following areas: (a) the demographic characteristics of the focus group; (b) the number of years for which respondents had played online games; (c) the motive for starting a game; (d) the number of game-characters assumed by each gamer; (e) the type of game played; and (f) other issues such as the reasons for involvement in the play, the willingness to reuse the game in case new versions were released, etc. On average, it took two hours to interview each of three groups. A primary set of FGIs was conducted with three groups on the premise that there would be some differences caused by character race (Horde vs. Alliance) or by playable server (Normal vs. Combat). With respect to the manner of playing, we found that guild members shared information, felt a sense of belonging, and played computer games for quite a long time through the guild; however, they did not undergo these experiences when playing alone. Gamers who belonged to a specific guild helped other players without expecting compensation for that, freely shared information about the game, gave away items for free, and more generous with other members who made mistakes. The guild members were aware of the existence other members and experienced a sense of belonging through interactions with, and evaluations from, other players. It was clear that social support was shown within the guild and that it played an important role as a major research variable. Based on the results of the first FGIs, a second set of in-depth FGIs was carried out with a focus on the psychology of the individual within the guild and the social community of the guild. The second set of FGIs also focused on the guild's offline meetings. Gamers, over all, recognize the necessity of joining a community, not only off-line but also online world of the guild. They admit that the guild is important for them to easily and conveniently enjoy playing online computer games. The active behavior and positive attitudes of existing guild members can motivate new members of the guild to adapt themselves to the guild environment. They then adopt the same behaviors and attitudes of established guild members. In this manner, the new members of the guild strengthen the bonds with other gamers while feeling a sense of belonging, and developing social identity, thereby. It was discovered that the interaction among guild members and the social support encouraged new gamers to quickly develop a sense of social identity and increase their self-esteem. The guild seemed to play the role of socializing gamers. Sometimes, even in the real world, the guild members helped one another; therefore, the features of the guild also spilled over to the offline environment. We intend to use self-esteem, which was found through the second set of FGIs, as an important research variable. To collect data, an online survey was designed with a questionnaire to be completed by WoW gamers, who belong to a guild. The survey was registered on the best three domestic game-sites: 'WoW playforum,' 'WoW gamemeca,' and 'Wow invent.' The selected items to be measured in the questionnaire were decided based on prior research and data from FGIs. To verify the content of the questionnaire, we carried out a pilot test with the same participants to point out ambiguous questions as a way to ensure maximum accuracy of the survey result. A total of 244 responses were analyzed from the 250 completed questionnaires. The SEM analysis was used to test goodness-of-fit of the model. As a result, we found important results as follows: First, according to the statistics, social support had statistically significant impacts on character control, character identity, guild identity and self-esteem. Second, character control had significant effects on character identity, guild identity and self-esteem. Third, character identity shows its clear impact on self-esteem and game loyalty. Fourth, guild identity affected self-esteem, guild flow and game loyalty. Fifth, self-esteem had a positive influence on the guild flow. These days, the number of virtual community is rising along with its significance largely because of the nature of the online games. Accordingly, this study is designed to clarify the psychological relationship between gamers within the guild that has been generally established by gamers to play online games together. This study focuses on the relationships in which social support influences guild flow or game loyalty through character control, character identity, guild identity, and self-esteem, which are present within a guild in the MMORPG game environment. The study results are as follows. First, the effects of social support on character control, character identity, guild identity and self-esteem are proven to be statistically significant. It was found that character control improves character identity, guild identity and self-esteem. Among the seven variables, social support, which is derived from FGIs, plays an important role in this study. With the active support of other guild members, gamers can improve their ability to develop good characters and to control them. Second, character identity has a positive effect on self-esteem and game loyalty, while guild identity has a significant effect on self-esteem, guild flow and game loyalty. Self-esteem affects guild flow. It was found that the higher the character and guild identities become, the greater the self-esteem is established. Contrary to the findings of prior research, our study results indicate that the relationship between character identity and guild flow is not significant. Rather, it was found that character identity directly affects game players' loyalty. Even though the character identity had no direct effect on increasing guild flow, it has indirectly affected guild flow through self-esteem. The significant relationship between self-esteem and guild flow indicates that gamers achieve flow, i.e., a feeling of pleasure and excitement through social support. Several important implications of this study should be noted. First, both qualitative and quantitative methods were used to conduct this study. Through FGIs, it was observed that both social support and self-esteem are important variables. Second, because guilds had been rarely studied, this research is expected to play an important role in the online community. Third, according to the result, six hypotheses (H1, H5, H6, H7, H8, and H11) setup based on FGIs, were statistically significant; thus, we can suggest the corresponding relationships among the variables as a guideline for follow-up research. Our research is significant as it has following implications: first, the social support of the guild members is important when establishing character control, character identity, guildidentity and self-esteem. It is also a major variable that affects guild flow and game loyalty. Second, character control when improved by social support shows notable influence on the development of character identity, guild identity and self-esteem. Third, character identity and guild identity are major factors to help establish gamers' own self-esteem. Fourth, character identity affects guild flow through self-esteem and game loyalty. The gamers usually express themselves through characters; the higher character identity is, the more loyalty a gamer has. Fifth, guild identity, established within the guild, has clear effects on self-esteem, guild flow and game loyalty. Sixth, qualitative and quantitative methods are employed to conduct this study. Based on the results of focus group interviews and SEM analysis, we find that the social support by guild members and psychological factors are significant in strengthening the flow of guild and loyalty to the game. As such, game developers should provide some extra functions for guild community, through which gamers can play online games in collaboration with one another. Also, we suggest that positive self-esteem which is built up through social support can help gamers achieve higher level of flow and satisfaction, which will consequently contribute to minimizing the possibility for the players to develop negative attitude toward the guild they belong to.
Purpose: During the first year of life, cow's milk protein is the major offender causing food allergy. Cow's milk allergy (CMA) affects 2~7% of infants, of which approximately one-half show predominantly gastrointestinal symptoms. We studied the clinical types of cow's milk allergy with predominantly gastrointestinal symptoms (CMA-GI) of childhood. Methods: The retrospective study was performed on 30 (male 22, female 8) patients who had diagnosed as CMA-GI during 2 years and 3 months from March 1995 to June 1997. Results: 1) Children with CMA-GI presented in the three types of clinical manifestation on the basis of time to reaction to milk ingestion: Quick (Q) onset (5 cases), Slow (S) onset (20 cases), Quick & Slow (Q&S) (5 cases). 2) Age on admission of the three groups was significantly different (p<0.05): (Q onset:
This study was to investigate the user's thermal environments of the children's parks according to pavements and sunscreen types during periods of heat waves. The measurements were conducted at the sand pits, rubber chip pavement, shelters, and green shade ground of the two children's parks located in Jinju, Korea(Chilam:
The study has been carried out to investigate the occurrence, damage, host range, transmission and control of rice stripe virus in Korea since 1965. 1 Disease occur「once and damage : The virus infection during the seedling stage ranged from 1.3 to
The present study is an attempt to solve the basic problems involved in the control of the Sclerotium disease. The biologic stranis of Sclerotium rolfsii Sacc., pathogen of Sclerotium disease of Magnolia kobus, were differentiated, and the effects of vitamins, various nitrogen and carbon sources on its mycelial growth and sclerotial production have been investigated. In addition the relationship between the cultural filtrate of Penicillium sp. and the growth of Sclerotium rolfsii, the tolerance of its mycelia or sclerotia to moist heat or drought and to Benlate (methyl-(butylcarbamoy 1)-2-benzimidazole carbamate), Tachigaren (3-hydroxy-5-methylisoxazole) and other chemicals were also clarified. The results are summarizee as follows: 1. There were two biologic strains, Type-l and Type-2 among isolates. They differed from each other in the mode of growth and colonial appearance on the media, aversion phenomenon and in their pathogenicity. These two types had similar pathogenicity to the Magnolia kobus and Robinia pseudoacasia, but behaved somewhat differently to the soybaen and cucumber, the Type-l being more virulent. 2. Except potassium nitrite, sodium nitrite and glycine, all of the 12 nitrogen sources tested were utilized for the mycelial growth and sclerotial production of this fungus when 10r/l of thiamine hydrochloride was added in the culture solution. Considering the forms of nitrogen, ammonium nitrogen was more available than nitrate nitrogen for the growth of mycelia, but nitrate nitrogen was better for sclerotia formation. Organic nitrogen showed different availabilities according to compounds used. While nitrite nitrogen was unavailable for both mycelial growth and sclerotial formation whether thiamine hydrochlioride was added or not. 3. Seven kinds of carbon sources examined were not effective in general, as long as thiamine hydrochloride was not added. When thiamine hydrochloride was added, glucose and saccharose exhibited mycelial growth, while rnaltose and soluble starch gave lesser, and xylose, lactose, and glycine showed no effect at all,. In the sclerotial production, all the tested carbon sources, except lactose, were effective, and glucose, maltose, saccharose, and soluble starch gave better results. 4. At the same level of nitrogen, the amount of mycelial growth increased as more carbon Sources were applied but decreased with the increase of nitrogen above 0.5g/1. The amount of sclerotial production decreased wi th the increase of carbon sources. 5. Sclerotium rolfsii was thiamine-defficient and required thiamine 20r/l for maximun growth of mycelia. At a higher concentration of more than 20r/l, however, mycelial growth decreased as the concentration increased, and was inhibited at l50r/l to such a degree of thiamine-free. 6. The effect of the nitrogen sources on the mycelial growth under the presence of thiamine were recognized in the decreasing order of
The rule of the Warsaw Convention of 1929 are well known and still being all over the world. The Warsaw Convention is undoubtedly the most widely accepted private international air law treaty with some 140 countries. In the international legal system for air transportation, the Warsaw Convention has played a major role for more than half century, and has been revised many times in consideration of the rapid developments of air high technology, changes of social and economic circumstances, need for the protection of passengers. Some amendments became effective, but others are still not effective. As a result, the whole international legal system for air transportation is at past so complicated and tangled. However, the 'Warsaw system' consists of the Warsaw Convention of 1929 the Guadalajara Convention of 1961, a supplementary convention, and the following six protocols: (1) the Hague Protocol of 1955, (2) the Guatemala Protocol of 1971, (3) the Montreal Additional Protocols, No.1, (4) the Montreal Additional Protocol No.2, (5) the Montreal Additional Protocol No.3, and (6) the Montreal Additional Protocol No.4. of 1975. As a fundamental principle of the air carrier's liability in the international convention and protocols, for instance in the Warsaw Convention and the Hague Protocol, the principle of limited liability and a presumed fault system has been adopted. Subsequently, the Montreal Inter-carrier Agreement of 1966, the Guatemala City Protocol, the Montreal Additional Protocol No.3, and the Montreal Additional Protocol No. 4 of 1975 maintained the limited liability, but substituted the presumed liability system by an absolute liability, that is, strict liability system. The Warsaw System, which sets relatively low compensation limits for victims of aircraft accidents and regulates the limited liability for death and injury of air passengers, had become increasingly outdated. Japanese Airlines and Inter-carrier Agreement of International Air Transport Association in 1995 has been adopted the unlimited liability of air carrier in international flight. The IATA Inter-Carrier Agreement, in which airlines in international air transportation agree to waive the limit of damages, was long and hard in coming, but it was remarkable achievement given the political and economic realities of the world. IATA deserves enormous credit for bringing it about. The Warsaw System is controversial and questionable. In order to find rational solution to disputes between nations which adopted differing liability systems in international air transportation, we need to reform the liability of air carriers the 'Warsaw system' and fundamentally, to unify the liability system among the nations. The International Civil Aviation Organization(ICAO) will therefore reinforce its efforts to further promote a legal environment that adequately reflects the public interest and the needs of the parties involved. The ICAO Study Group met in April, 1998, together with the Drafting Committee. The time between the "Special Group on the Modernization and Consolidation of the 'Warsaw system'(SGMW)" and the Diplomatic Conference must be actively utilized to arrange for profound studies of the outstanding issues and for wide international consultations with a view to narrowing the scope of differences and preparing for a global international consensus. From 11 to 28 May 1999 the ICAO Headquarters at Montreal hosted a Diplomatic Conference convened to consider, with a view to adoption, a draft Convention intended to modernize and to integrate replace the instruments of the Warsaw system. The Council of ICAO convened this Conference under the Procedure for the Adoption of International Conventions. Some 525 participants from 121 Contracting States of ICAO attended, one non-contracting State, 11 observer delegations from international organizations, a total of 544 registered participants took part in the historic three-week conference which began on 10 May. The Conference was a success since it adopted a new Convention for the Unification of Certain Rules for International Carriage by Air. The 1999 Montreal Convention, created and signed by representatives of 52 countries at an international conference convened by ICAO at Montreal on May 28, 1999, came into effect on November 4, 2003. Representatives of 30 countries have now formally ratified the Convention under their respective national procedures and ratification of the United States, which was the 30th country to ratify, took place on September 5, 2003. Under Article 53.6 of the Montreal Convention, it enters into force on the 60th day following the deposit of the 30th instrument of ratification or acceptation. The United States' ratification was deposited with ICAO on September 5, 2003. The ICAO have succeeded in modernizing and consolidating a 70-year old system of international instruments of private international law into one legal instrument that will provide, for years to come, an adequate level of compensation for those involved in international aircraft accidents. An international diplomatic conference on air law by ICAO of 1999 succeeded in adopting a new regime for air carrier liability, replacing the Warsaw Convention and five other related legal instruments with a single convention that provided for unlimited liability in relation to passengers. Victims of international air accidents and their families will be better protected and compensated under the new Montreal Convention, which modernizes and consolidates a seventy-five year old system of international instruments of private international law into one legal instrument. A major feature of the new legal instrument is the concept of unlimited liability. Whereas the Warsaw Convention set a limit of 125,000 Gold Francs (approximately US$ 8,300) in case of death or injury to passengers, the Montreal Convention introduces a two-tier system. The first tier includes strict liability up to l00,000 Special Drawing Rights (SDR: approximately US$ 135,000), irrespective of a carrier's fault. The second tier is based on presumption of fault of a carrier and has no limit of liability. The 1999 Montreal Convention also includes the following main elements; 1. In cases of aircraft accidents, air carriers are called upon to provide advance payments, without delay, to assist entitled persons in meeting immediate economic needs; the amount of this initial payment will be subject to national law and will be deductable from the final settlement; 2. Air carriers must submit proof of insurance, thereby ensuring the availability of financial resources in cases of automatic payments or litigation; 3. The legal action for damages resulting from the death or injury of a passenger may be filed in the country where, at the time of the accident, the passenger had his or her principal and permanent residence, subject to certain conditions. The new Montreal Convention of 1999 included the 5th jurisdiction - the place of residence of the claimant. The acceptance of the 5th jurisdiction is a diplomatic victory for the US and it can be realistically expected that claimants' lawyers will use every opportunity to file the claim in the US jurisdiction - it brings advantages in the liberal system of discovery, much wider scope of compensable non-economic damages than anywhere else in the world and the jury system prone to very generous awards. 4. The facilitation in the recovery of damages without the need for lengthy litigation, and simplification and modernization of documentation related to passengers. In developing this new Montreal Convention, we were able to reach a delicate balance between the needs and interests of all partners in international civil aviation, States, the travelling public, air carriers and the transport industry. Unlike the Warsaw Convention, the threshold of l00,000 SDR specified by the Montreal Convention, as well as remaining liability limits in relation to air passengers and delay, are subject to periodic review and may be revised once every five years. The primary aim of unification of private law as well as the new Montreal Convention is not only to remove or to minimize the conflict of laws but also to avoid conflict of jurisdictions. In order to find a rational solution to disputes between nations which have adopted differing liability systems in international air transport, we need fundamentally to reform their countries's domestic air law based on the new Montreal Convention. It is a desirable and necessary for us to ratify rapidly the new Montreal Convention by the contracting states of lCAO including the Republic of Korea. According to the Korean and Japanese ideas, airlines should not only pay compensation to passengers immediately after the accident, but also the so-called 'condolence' money to the next of kin. Condolence money is a gift to help a dead person's spirit in the hereafter : it is given on account of the grief and sorrow suffered by the next of kin, and it has risen considerably over the years. The total amount of the Korean and Japanese claims in the case of death is calculated on the basis of the loss of earned income, funeral expenses and material demage (baggage etc.), plus condolence money. The economic and social change will be occurred continuously after conclusion of the new Montreal Convention. In addition, the real value of life and human right will be enhanced substantially. The amount of compensation for damage caused by aircraft accident has increased in dollar amount as well as in volume. All air carrier's liability should extend to loss of expectation of leisure activities, as well as to damage to property, and mental and physical injuries. When victims are not satisfied with the amount of the compensation for damage caused by aircraft accident for which an airline corporation is liable under the current liability system. I also would like to propose my opinion that it is reasonable and necessary for us to interpret broadly the meaning of the bodily injury on Article 17 of the new Montreal Convention so as to be included the mental injury and condolence. Furthermore, Korea and Japan has not existed the Air Transport Act regulated the civil liability of air carrier such as Air Transport Act (Luftverkehrsgestz) in Germany. It is necessary for us to enact "the Korean Air Transport Contract Act (provisional title)" in order to regulate the civil liability of air carrier including the protection of the victims and injured persons caused by aircraft accident.
A costume reveals the social characteristics of the era in which it is worn, thus we can say that the history of change of the costume is the history of change of the living culture of the era. Since the Three States era, the costume structure of this country had been affected by the costume system of the China's historical dynasties in the form of the grant therefrom because of geographical conditions, which affection was conspicuous for the bureaucrat class, particularly including but not limited to the Kings' familities. Such a grant of the costume for the bureaucrat class (i.e., official uniform) was first given by the Dang-dynasty at the age of Queen Jinduck, the 28th of the Shilla-dynasty. Since then, the costume for the bureaucrats had consecutively been affected as the ages had gone from the unified Shilla, to the Koryo and to the Yi-dynasty. As the full costumes officially used by government officials (generally called "Baek Gwan") in the Yidynasty, there existed Jo-bok, Gong-bok and Sang-bok. Of such official costumes, Gong-bok was worn at the time of conducting official affairs of the dynasty, making a respectful visit for the expression of thanks or meeting diplomatic missions of foreign countries. It appears no study was made yet with regard to the Gong-bok while the studies on the Jo-bok and the Sangbok were made. Therefore, this article is, by rendering a study and research on the styles of costumes of civil servants' stone images erected at the Kings' tombs of the Yi-dynasty, to help the persons concerned understand the Gong-bok, one of the official costume for Baek Kwan of that age and further purports to specifically identify the styles and changes of the Gong-bok, worn by Baek Gwan during the Yi-dynasty, consisting of the Bok-doo (a hat, four angled and two storied with flat top), Po (gown), Dae (belt), and Hol (small and thin plate which was officially held by the government officials in hand, showing the courtesy to and writing brief memorandums before the King) and Hwa (shoes). For that purpose, I investigated by actually visiting the tombs of the Kings of the Yi-dynasty including the Geonwon-neung, the tomb of the first King Tae-jo and the You-neung, the tomb of the 27th King Soon-jong as well as the tombs of the lawful wives and concubines of various Kings, totalling 29 tombs and made reference to relevant books and records. Pursuant. to this study, of the 29 Kings' tombs the costume styles of civil servants' stone images erected at the 26 Kings' tombs are those of Gong-bok for Baek-gwan of the Yi-dynasty wearing Bok-doo as a hat and Ban-ryeong or Dan-ryenog Po as a gown with Dae, holding Hol in hand and wearing shoes. Other than those of the 26 tombs, the costume styles of the Ryu-neung, the tomb of the Moon-jo who was the first son of 23rd King Soon-jo and given the King's title after he died and of the You-neung, the tomb of the 27th King Soon-jong are those of Jobok with Yang-gwan (a sort of hat having stripes erected, which is different from the Bok-doo), and that of the Hong-neung, the tomb of the 26th King Go-jong shows an exceptional one wearing Yang-gwan and Ban-ryeong Po ; these costume styles other than Gongbok remain as the subject for further study. Gong-bok which is the costume style of civil servants' stone images of most of the Kings' tombs had not been changed in its basic structure for about 500 years of the Yi-dynasty and Koryo categorized by the class of officials pursuant to the color of Po and materials of Dae and Hol. Summary of this costume style follows: (1) Gwan-mo (hat). The Gwan-mo style of civil servants' stone images of the 26 Kings' tombs, other than Ryu-neung, Hong-neung and You-neung which have Yang-gwan, out of the 29 Kings' tombs of the Yi-dynasty reveals the Bok-doo with four angled top, having fore-part and back-part divided. Back part of the Bok-doo is double the fore-part in height. The expression of the Gak (wings of the Bokdoo) varies: the Gyo-gak Bok-doo in that the Gaks, roundly arisen to the direction of the top, are clossed each other (tombs of the Kings Tae-jong), the downward style Jeon-gak Bok-doo in that soft Gaks are hanged on the shoulders (tombs of the Kings Joong-jong and Seong-jong) and another types of Jeon-gak Bok-doo having Gaks which arearisen steeply or roundly to the direction of top and the end of which are treated in a rounded or straight line form. At the lower edge one protrusive line distinctly reveals. Exceptionally, there reveals 11 Yang-gwan (gwan having 11 stripes erected) at the Ryu-neung of the King Moon-jo, 9 Yang-gwan at the Hong-neung of the King Go-jong and 11 Yang-gwan at the You-neung of the King Soon-jong; noting that the Yang-gwan of Baek Kwan, granted by the Myeong-dynasty of the China during the Yi-dynasty, was in the shape of 5 Yang-gwan for the first Poom (class) based on the principle of "Yideung Chaegang" (gradual degrading for secondary level), the above-mentioned Yang-gwans are very contrary to the principle and I do not touch such issue in this study, leaving for further study. (2) Po (gown). (a) Git (collar). Collar style of Po was the Ban-ryeong (round collar) having small neck-line in the early stage and was changed to the Dan-ryeong (round collar having deep neck-line) in the middle of the: dynasty. In the Dan-ryeong style of the middle era (shown at the tomb of the King Young-jo); a, thin line such as bias is shown around the internal side edge and the width of collar became wide a little. It is particularly noted that the Ryu-neung established in the middle stage and the You-neung in the later stage show civil servants in Jo-bok with the the Jikryeong (straight collar) Po and in case of the Hong-neung, the Hong-neung, the tomb of the King Go-jong, civil servants, although they wear Yang-gwan, are in the Ban-ryeong Po with Hoo-soo (back embroidery) and Dae and wear shoes as used in the Jo-bok style. As I could not make clear the theoretical basis of why the civil servants' costume styles revealed, at these tombs of the Kings are different from those of other tombs, I left this issue for further study. It is also noted that all the civil servants' stone images show the shape of triangled collar which is revealed over the Godae-git of Po. This triangled collar, I believe, would be the collar of the Cheomri which was worn in the middle of the Po and the underwear, (b) Sleeve. The sleeve was in the Gwan-soo (wide sleeve) style. having the width of over 100 centimeter from the early stage to the later stage arid in the Doo-ri sleeve style having the edge slightly rounded and we can recognize that it was the long sleeve in view of block fold shaped protrusive line, expressed on the arms. At the age of the King Young-jo, the sleeve-end became slightly narrow and as a result, the lower line of the sleeve were shaped curved. We can see another shape of narrow sleeve inside the wide sleeve-end, which should be the sleeve of the Cheom-ri worn under the Gong-bok. (c) Moo. The Moo revealed on the Po of civil servants' stone images at the age of the King Sook-jong' coming to the middle era. Initially the top of the Moo was expressed flat but the Moo was gradually changed to the triangled shape with the acute top. In certain cases, top or lower part of the Moo are not reveald because of wear and tear. (d) Yeomim. Yeomim (folding) of the Po was first expressed on civil servants' stone images of the Won-neung, the tomb of the King Young-jo and we can seemore delicate expression of the Yeomim and Goreum (stripe folding and fixing the lapel of the Po) at the tomb of the Jeongseong-wanghoo, the wife of the King Young-jo, At the age of the King Soon-jo, we can see the shape of Goreum similar to a string rather than the Goreum and the upper part of the Goreum which fixes Yeomim was expressed on the right sleeve. (3) Dae. Dae fixed on the Po was placed half of the length of Po from the shoulders in the early stage. Thereafter, at the age of the King Hyeon-jong it was shown on the slightly upper part. placed around one third of the length of Po. With regard to the design of Dae, all the civil servants' stone images of the Kings' tombs other than those of the Geonwon-neung of the King Tae-jo show single or double protrusive line expressed at the edge of Dae and in the middle of such lines, cloud pattern, dangcho (a grass) pattern, chrysanthemum pattern or other various types of flowery patterns were designed. Remaining portion of the waist Dae was hanged up on the back, which was initially expressed as directed from the left to the right but thereafter expressed. without orderly fashion,. to the direction of the left from the right and vice versa, Dae was in the shape of Yaja Dae. In this regard, an issue of when or where such a disorderly fashion of the direction of the remaining portion of waist Dae was originated is also presented to be clarified. In case of the Ryuneung, Hong-neung and You-neung which have civil servants' stone images wearing exceptional costume (Jo-bok), waist Dae of the Ryu-neung and Hong-neung are designed in the mixture of dual cranes pattern, cosecutive beaded pattern and chrvsenthemum pattern and that of You-neung is designed in cloud pattern. (4) Hol. Although materials of the Hol held in hand of civil servants' stone images are not identifiable, those should be the ivory Hol as all the Baek Gwan's erected as stone images should be high class officials. In the styles, no significant changes were found, however the Hol's expressed on civil servants' stone images of the Yi-dynasty were shaped in round top and angled bottom or round top and bottom. Parcicularly, at the age of the King Young-jo the Hol was expressed in the peculiar type with four angles all cut off. (5) Hwa (shoes). As the shoes expressed on civil servants' stone images are covered with the lower edges of the Po, the styles thereof are not exactly identifiable. However, reading the statement "black leather shoes for the first class (1 Poom) to ninth class (9 Poom)," recorded in the Gyeongkook Daejon, we can believe that the shoes were worn. As the age went on, the front tips of the shoes were soared and particularly, at the Hong-neung of the King Go-jong the shoes were obviously expressed with modern sense as the country were civilized.