P Peretti-Watel

C Martha

F Lorente

G Doucende

V Seror

RESUME L Grélot

ALCOHOL USE AND INTOXICATION IN FRENCH SPORT UNIVERSITY STUDENTS, FROM 2002 TO 2013-16 Auteurs

Keywords: alcool, binge drinking, ivresse, étudiants, sport, France alcohol, binge drinking, intoxication, students, sport, France

Objectifs : réaliser un suivi diachronique des usages et abus d'alcool parmi les étudiants de la filière STAPS depuis 2002, en prenant en compte le niveau de pratique et la discipline sportive. Matériel et méthodes : 905 étudiants de deuxième et troisième années ont rempli le même questionnaire déjà utilisé en 2002. Résultats : entre 2002 et 2013-16, les consommations de bière et les ivresses sont devenus plus fréquentes, en particulier parmi les filles, de sorte que les écarts entre sexes observés en 2002 se sont réduits, ce qu'illustre notamment l'évolution de l'âge à la première ivresse. L'usage d'alcool, le binge drinking et l'ivresse sont corrélés négativement avec le niveau de pratique, mais sont plus fréquents parmi les pratiquants d'un sport de glisse (pour les deux sexes) ou d'un sport collectif (hors football, et pour les garçons seulement). Conclusions : ces résultats sont d'autant plus importants qu'une partie de ces étudiants interagira avec des jeunes dans un futur proche. Nos résultats soulignent aussi la nécessité de mener sur ce sujet des analyses stratifiées par sexe.

INTRODUCTION

In the last two decades, there has been growing evidence that athletes consume alcohol more frequently and in larger quantities than their non-athlete counterparts, especially among highschool and university students (for literature reviews on this topic, see [START_REF] Kwan | Sport participation and alcohol and illicit drug use in adolescents and young adults: a systematic review of longitudinal studies[END_REF][START_REF] Lisha | Relationship of high school and college sports participation with alcohol, tobacco, and illicit drug use: a review[END_REF][START_REF] Martens | A systematic review of college studentathlete drinking: Prevalence rates, sport-related factors, and interventions[END_REF][START_REF] Turrisi | Heavy drinking in college students: who is at risk and what is being done about it?[END_REF][START_REF] Zhou | Sports and Spirits: A Systematic Qualitative Review of Emergent Theories for Student-Athlete Drinking[END_REF]). Sport participation had been shown to be positively associated with alcohol use [START_REF] Lisha | Relationship of high school and college sports participation with alcohol, tobacco, and illicit drug use: a review[END_REF] and this positive association was notably confirmed in a recent study conducted among French college students [START_REF] Tavolacci | Prevalence of binge drinking and associated behaviours among 3286 college students in France[END_REF]. This literature also shows strong gender differences: male athletes are more likely to engage in alcohol use, binge drinking and alcohol intoxication than female athletes [START_REF] Tavolacci | Prevalence of binge drinking and associated behaviours among 3286 college students in France[END_REF][START_REF] Brenner | High-risk drinking characteristics in collegiate athletes[END_REF][START_REF] Ford | Substance use among college athletes: a comparison based on sport/team affiliation[END_REF][START_REF] Lorente | Alcohol use and intoxication in sport university students[END_REF], and drinking motives may also differ according to gender [START_REF] O'brien | Gender equality in university sportspeople's drinking[END_REF].

Such relationship between sport participation and alcohol use may seem 'incongruous' [START_REF] Musselman | The incongruous alcohol-activity association: physical activity and alcohol consumption in college students[END_REF], as participating in sports is supposed to be a health enhancing activity whereas involvement in high-level sports also requires developing athletic abilities, in accordance with the deterrence hypothesis [START_REF] Peretti-Watel | Youth sport, cigarettes, alcohol and illicit drugs[END_REF]. Nevertheless, several theories have been proposed to explain the link between sport participation and drinking behaviors. These theories highlight the importance of the sporting context on drinking in relation with competitive levels and type of sports. For example, athletes may consider alcohol use as a coping strategy to alleviate competitive stress and anxiety; the sociability induced by participation in team sports may fuel alcohol use and abuse; and sports participation and alcohol use may be impelled by similar motives or values, such as sensation seeking for sliding sports [START_REF] Zhou | Sports and Spirits: A Systematic Qualitative Review of Emergent Theories for Student-Athlete Drinking[END_REF][START_REF] Peretti-Watel | Youth sport, cigarettes, alcohol and illicit drugs[END_REF].

As regards alcohol consumption and intoxication among French sport science students, a previous study conducted in 2002 showed strong gender differences [START_REF] Lorente | Alcohol use and intoxication in sport university students[END_REF]. Since then, replicate surveys had been conducted in 2013-16 and the aim of the present study was twofold: 1) to monitor potential trends in patterns of alcohol consumption and intoxication in French sport science students by comparing the data collected in 2002 and in 2013-16 ; 2) to investigate the relationship between competitive level, type of sport and alcohol consumption and intoxication.

MATERIAL & METHODS

Data collection

We conducted a survey among university students from three sport sciences departments in southern France (Marseilles, Font-Romeu, and Gap). In order to reach a large sample size, we organized several sessions of data collection during tutorials between the fall 2013 and the fall 2016 semesters. At each session, it was made clear to students that they were free to refuse to participate, and that the survey was anonymous and strictly confidential, with no 'right' or 'wrong' answers. Each session lasted about 20 min. Participants sat one per table, each table separated from the others by at least 6 feet in all directions. An investigator was always present to ensure absence of communication between surveyed students. At the end of the session, questionnaires were placed in a ballot box. These procedures were identical to those used for the 2002 survey, and they were performed according to the French law on Human Care Guidelines, using protocols approved by the Human Care Committee at Aix-Marseille University.

Questionnaire

The self-reported questionnaire included 88 items characterizing the population in terms of demographics and sport practice (8 items), alcohol consumption and intoxication (14 items), and others substance use and abuse (66 items). It was the same questionnaire as in the 2002 survey, except for one additional item on binge drinking.

In the present study, we focused on the following items: gender, age, frequencies of alcohol consumption (never, less than once per month, 1 to 4 per month, 2 to 6 per week, every day, for beer, wine and spirits respectively); binge drinking (consuming at least five drinks at one time) and alcohol intoxication during the previous 12 months (never, 1 or 2, 3 to 5, 6 to 10, more than 10 times), age at first alcohol intoxication, main sport practiced and competitive level.

Statistical analysis

Answers to alcohol consumption-related items were merged into binary outcomes: ≥2 times per week versus less frequent for beer, wine, spirits; ≥10 times during the previous 12 months versus less frequent for binge drinking and intoxication. Regarding the main sport practiced, we encoded answers into 6 categories (as in ( 13)): soccer, other team sport (mainly rugby, handball, basketball), athletics, sliding sports (mainly skiing, sailing, windsurfing), combat sports (mainly boxing and martial arts), and other individual sports (tennis, swimming, gymnastics, etc.).

We first used χ² tests to compare the frequencies of alcohol use and intoxication (males versus females for each survey; 2002 versus 2013-16, for each gender) and a Student's t-test to compare mean age at first intoxication for male and female students. Regarding the relationship between competitive level, type of sport and alcohol consumption and intoxication, we focused on three binary outcomes: consuming either beer, wine or spirits ≥2 times per week; reporting at least 10 episodes of binge drinking during the previous 12 months; reporting at least 10 episodes of alcohol intoxication during the previous 12 months. We first used χ² tests, then we computed logistic regressions with a stepwise selection method (entry threshold p=0.1), forcing age into each model. These analyses were performed for female and male students separately.

RESULTS

All students who were present during the tutorials (n=1,268) agreed to participate, but 6 questionnaires were excluded from analysis because either age or gender were not given or because of incomplete answers for alcohol-related items. First, in order to compare our results to those observed in 2002, we also restricted the sample to second-and third-year students (n=905). In this sample, the mean age of respondents was 20.0±1.5 (mean ± SD) years (vs. 20.6±1.7 on 2002); 34.1% were female (vs. 41.7% on 2002). of male students had already experienced alcohol intoxication, versus about one third of female students, with a gap superior to 20 points at age 20. In 2013-16, sport students were more likely than in 2002 to report that they had already experienced alcohol intoxication, and they had it earlier, as the cumulative frequencies were higher at each age, for both males and females. In addition, this evolution was much more dramatic for female students: at age 16, almost 60% of those interviewed in 2013-2016 had already experienced intoxication, versus less than a third in 2002. As a result, the gap between male and female students narrowed substantially in 2013-2016, as the two corresponding curves are very close to each other. Regarding the mean age at first alcohol intoxication, the difference between male and female students was not statistically significant (15.8 versus 15.9, p=0.556).

Alcohol consumption & alcohol intoxication, from 2002 to 2013-16

Type of sport, competitive level and alcohol use/intoxication.

Among female students, those who were competing at a regional or a national level were more likely to report consuming alcohol at least twice a week than their international-level counterparts (27.2% and 26.8% respectively, with significant adjusted odds ratios (aOR), see Table 2), as well as those practicing mainly a sliding sport. Conversely, female students doing athletics were less likely to report such alcohol use, and they were also less likely to report at least ten episodes of binge drinking during the previous 12 months. Moreover, females practicing a sliding sport or a combat sport were more likely to report at least ten episodes of intoxication during the previous 12 months. Finally, after adjustment on other covariates, no significant relation was found between competitive level and either binge drinking or intoxication.

Table 2.

Among male students of the 2013-16 population, after adjustment on other covariates, competitive participation at a regional level and practicing a team sport other than soccer were significantly related to both alcohol use (with respectively 42.9% and 44.9% of corresponding students reporting at least two episodes of alcohol use per week, see Table 3) and binge drinking (with respectively 66.7% and 72.1% of corresponding students reporting at least ten episodes of binge drinking during the previous 12 months). Regarding binge drinking, competing at an international level and doing athletics were significant protective factors (with aOR of 0.31 and 0.56 respectively), while practicing a sliding sport was another risk factor (aOR=1.65).

Similarly, male students competing at an international level were less likely to report at least ten episodes of alcohol intoxication during the previous 12 months (16.2%, aOR=0.34), while those practicing a team sport other than soccer or a sliding sport were more likely to do so (respectively 50.0% and 39.4%, aOR=2.65 and 2.00). Table 3.

DISCUSSION

The present study monitored the evolution of the pattern of alcohol consumption among sport sciences students from southern France universities between 2002 and 2013-16. It also investigated the relationships between sport practice and alcohol consumption. Before discussing our results, we must acknowledge the main limitations of this study. First, the students sampled may not be representative of all French sport sciences students. Secondly, we used a self-reported questionnaire rather than objective measurement. Nevertheless, adolescents and young adults' self-reported drinking behaviors are considered quite reliable [START_REF] Lintonen | The reliability of self-reported drinking in adolescence[END_REF][START_REF] Smith | Self-reported drinking and alcohol-related problems among early adolescents: dimensionality and validity over 24 months[END_REF].

According to previous studies conducted among large and national samples of French people aged 18 to 25, between 2005 and 2014, the prevalence of beer consumption, binge drinking and alcohol intoxication greatly increased, especially among college students and females, and as a result in this population males and females' drinking behaviors tend to get closer [START_REF] Richard | La consommation d'alcool en France en 2014[END_REF][START_REF] Richard | Alcohol consumption among young adults (18-25 years) in 2010 in France: specificities and trends since 2005[END_REF]. Our results are consistent with these trends, as between 2002 and 2013-16, among sport students, the frequencies of beer consumption and alcohol intoxication greatly increased, especially among females, and the gender differences observed in 2002 tended to reduce dramatically, as illustrated by the evolution of age at first intoxication. Nevertheless, the estimated frequencies were higher among sport students: for example, among French female college students, the prevalence of regular alcohol intoxication (at least 10 episodes per year) reached 2% in 2005, 7% in 2010 and 11% in 2014 ( 16), versus 2.5% in 2002 and 17.8% in 2013-16 among female sport students from southeastern universities. As for male students, this prevalence was found to remain stable between 2005 et 2014 (e.g. 13% in 2005 ( 16)) while it almost doubled in sport university students (19.2 in 2002, 34.1 in 2013-2016). Such results raise concern: beyond adverse health and social consequences of alcohol consumption, these sport students are likely to interact with youth in near future, for example as physical education teachers or professional coaches.

Regarding competition level, the highest levels of alcohol use, binge drinking and intoxication were associated to regional and national level, while the lowest levels corresponded to international competitors, at least among male sport students. Previous studies found conflicting evidence on this point [START_REF] Brenner | High-risk drinking characteristics in collegiate athletes[END_REF][START_REF] Green | NCAA study of substance use and abuse habits of college student-athletes[END_REF]. Such inverted U-shape relationship has been already observed [START_REF] O'brien | Hazardous drinking in New Zealand sportspeople: level of sporting participation and drinking motives[END_REF], and it may reflect conflicting features. On the one hand, a higher competition level may induce more stress and be an incentive for drinking to cope with it, and high-level competitors may be more likely to consider drinking as a competition (trying to out-drink their peers) [START_REF] Weaver | Sport-related achievement motivation and alcohol outcomes: an athlete-specific risk factor among intercollegiate athletes[END_REF].

On the other hand, at high competition level, the negative effect of alcohol use on athletic performance may become crippling, and young athletes may be more tightly controlled by their coach and their relatives.

Regarding the type of sport practiced, practicing a sliding sport was correlated to drinking behaviors in both female and male students. This result echoed previous studies which found a relationship between sliding sports, alcohol and cannabis use, among elite students-athletes trained in specialized public centers and among sport university students [START_REF] Lorente | Cannabis use to enhance sportive and nonsportive performances among French sport students[END_REF][START_REF] Peretti-Watel | Sporting activity and drug use: Alcohol, cigarette and cannabis use among elite student athletes[END_REF]. Both sliding sports participation and drug use may be impelled by sensation-seeking and express attachment to the same subculture [START_REF] Peretti-Watel | Youth sport, cigarettes, alcohol and illicit drugs[END_REF]. Moreover, among males only, team sports other than soccer were positively correlated to drinking behaviors. The relationship between team sports and drinking behavior is a well-documented one [START_REF] Martha | Participants' sports characteristics related to heavy episodic drinking among French students[END_REF][START_REF] Chen | The effect of sport participation on student-athlete students' social life and identity[END_REF][START_REF] Partington | The relationship between membership of a university sports group and drinking behaviour among students at English Universities[END_REF][START_REF] Taylor | Examination of Drinking Habits and Motives of Collegiate Student-Athletes[END_REF], and in our study it should be noted that rugby was dominant among "other team sports" and the "third half-time" which takes place after the matches is a well-known tradition [START_REF] Prentice | The effects of binge drinking behaviour on recovery and performance after a rugby match[END_REF].

Finally, as the relationship between competition level, type of sport and drinking behaviors differed across gender, our results also corroborated the importance to investigate this topic for each gender separately. #: adjusted odds ratios computed from dichotomous logistic regressions, confidence intervals at 90%. ##: variable not selected by the stepwise method.

Figure 1 .

 1 Figure 1.

Figure 1 .

 1 Figure 1. Gender difference in the cumulative frequencies of the age at first alcohol intoxication among sports science students (2002 & 2013-16).

Table 1

 1 compares alcohol use and alcohol intoxication for male and female students, in 2002 and 2013-2016. In 2002, beer use, wine use, spirits use and alcohol intoxication were more frequent among male students when compared to their female counterparts. In 2013-16, this gender difference in alcohol use and intoxication remained significant, except for wine use.Regarding evolutions in alcohol use and intoxication from 2002 to 2013-2016, among male students, drinking beer at least two times per week became much more prevalent (19.5% in 2002, 30.7% in 2013-2016), as well as reporting at least 10 episodes of intoxication per year (from 19.2% to 34.1%), while wine use slightly decreased and spirits use remained stable.Among female students, we also observed dramatic increases in beer use and intoxication: in 2013-2016, 14.9% of female students reported drinking beer at least two times per week (versus 4.9% in 2002), and 17.8% reported at least 10 episodes of intoxication per year (versus 2.5% in 2002).

Table 1 .

 1 Figure 1 represents the percentages of subjects who had been intoxicated by gender and age, in 2002 and 2013-16 respectively. In 2002, we observed a strong gender difference: at age 16, half

Table 1 . Self-report frequency of alcohol use and alcohol intoxication among sports science university students (southern France, 2002 & 2013-16).

 1

	2002	2013-16	Comparison of proportions **
	Male (%)	Female (%)	Male (%)	Female (%)	I vs. II III vs. IV I vs. III II vs. IV
	(n=395) I	(n=282) II	(n=596) III	(n=309) IV

* Whisky, vodka, gin, pastis, etc. ** p-value for the χ² test.

Table 2 . Competitive level, type of sport and drinking behaviors among sports science university female students (southern France, 2013-16).

 2

		Alcohol use:	Binge drinking:	Alcohol intoxication:
		≥2 times per week*	≥10 (previous 12 months)	≥10 (previous 12 months)
		%**	aOR [CI90%] #	%	aOR	%	aOR
	age	___	1.47 [1.24;1.75]	___	1.24 [1.07;1.44]	___	1.12 [0.95;1.33]
	Competitive level:	p=0.096		p=0.806		p=0.830
	-departmental (ref.)	14.5	-1-	33.3	-1-	19.7	-1-
	-regional	27.2	2.73 [1.50;4.94]	37.0	ns	18.5	ns
	-national	26.8	2.16 [1.19;3.93]	37.8	ns	14.6	ns
	-international	22.2	ns ##	27.8	ns	16.7	ns
	Type of sport:	p=0.162		p=0.004		p=0.096
	-soccer	12.5	ns	12.5	ns	12.5	ns
	-other team sports	22.7	ns	43.2	ns	15.9	ns
	-athletics	4.0	0.15 [0.03;0.85]	4.0	0.07 [0.01;0.37]	4.0	ns
	-sliding sports	31.7	1.97 [1.02;3.79]	46.3	ns	26.8	2.05 [1.07;3.94]
	-combat sports	29.4	ns	47.1	ns	35.3	3.23 [1.33;7.87]
	-other individual sports (ref.)	22.2	-1-	34.5	-1-	17.0	-1-

* for either beer, wine or spirits. ** column percentages.

Table 3 . Competitive level, type of sport and drinking behaviors among sports science university male students (southern France, 2013-16).

 3

		Alcohol use:	Binge drinking:	Alcohol intoxication:
		≥2 times per week*	≥10 (previous 12 months)	≥10 (previous 12 months)
		%**	aOR [CI90%] #	%	aOR [CI90%]	%	aOR [CI90%]
	age	___	1.03 [0.94;1.12]	___	0.93 [0.85;1.02]	___	0.92 [0.84;1.02]
	Competitive level:	p=0.033		p<10 -3		p=0.014
	-departmental (ref.)	29.8	-1-	47.9	-1-	30.3	-1-
	-regional	42.9	1.47 [1.09;1.98]	66.7	1.65 [1.22;2.25]	34.8	ns
	-national	36.6	ns	58.4	ns	41.6	ns
	-international	27.0	ns ##	27.0	0.31 [0.16;0.61]	16.2	0.34 [0.16;0.73]
	Type of sport:	p=0.066		p<10 -3		p<10 -3
	-soccer	30.8	ns	53.3	ns	24.3	ns
	-other team sports	44.9	1.49 [1.06;2.08]	72.1	2.23 [1.54;3.23]	50.0	2.65 [1.88;3.72]
	-athletics	24.4	ns	36.6	0.56 [0.32;0.99]	17.1	ns
	-sliding sports	39.4	ns	57.7	1.65 [1.04;2.61]	39.4	2.00 [1.27;3.16]
	-combat sports	40.9	ns	47.7	ns	34.1	ns
	-other individual sports (ref.)	32.1	-1-	51.3	-1-	29.4	-1-

ACKNOWLEDGEMENTS.

We thank the participants of this research. It was conducted thanks to a grant from the MILDECA (Interministerial Mission for Combating Drugs and Addictive Behaviours) and Paris 13 University (Call for Proposals IRESP Prevention 2015). The authors have no conflict of interest to declare.


Mohamed Boutghatin
email: mohamed.boutghatin@univ-lille.fr

Salim Assaf
email: salim.alhajj-assaf@univ-lille.fr

Michèle Carette
email: michele.carette@univ-lille.fr

Vincent Thomy
email: vincent.thomy@univ-lille.fr

Abdellatif Akjouj
email: abdellatif.akjouj@univ-lille.fr

Bahram Djafari-Rouhani
email: bahram.djafari-rouhani@univ-lille.fr

Yan Pennec
email: yan.pennec@univ-lille.fr

Polymer Photonic Crystal Membrane for Human Body Thermoregulation

Keywords: photonic membrane, Mid-Infrared, thermal comfort. I

We study the optical properties of a polymer photonic membrane to keep the human body in thermal comfort. We show theoretically that the periodic structuration of the membrane with air holes modulates the optical response in the Mid-Infrared range. We found that the modulation of the optical spectrum allows to decrease the required ambient temperature by about 0.5 °C to maintain the normal skin temperature of 34 °C. The structured membrane is flexible and can easily be added to usual textiles.

INTRODUCTION

A large part of the energy consumed is used to regulate the temperature of residential buildings. Reducing this consumption will have a positive impact on the economy and the environment. In previous studies, the importance of personal thermoregulation was investigated and demonstrated in different ways [START_REF] Hsu | Personal Thermal Management by Metallic Nanowire-Coated Textile[END_REF] [START_REF] Tong | Infrared-Transparent Visible-Opaque Fabrics for Wearable Personal Thermal Management[END_REF]. Photonic crystals have been recently proposed to control the propagation of electromagnetic waves in the Mid-Infrared range for several applications from thermophotovoltaic systems to thermal textile [START_REF] Li | Nanophotonic control of thermal radiation for energy applications[END_REF]. For radiative cooling, Raphaeli et al. presented a metal-dielectric photonic structure, reflective in the visible and having high emissivity in the Mid-Infrared [START_REF] Rephaeli | Ultrabroadband Photonic Structures To Achieve High-Performance Daytime Radiative Cooling[END_REF]. More recently, we have demonstrated the efficiency of a structured polymer membrane to maintain an individual thermal comfort in indoor rooms [START_REF] Assaf | Polymer photonic crystal membrane for thermo-regulating textile[END_REF]. Our objective here is to demonstrate that a polymer membrane can act both as a sensor by the modification of its structural parameters and as a passive actuator by modifying its thermal properties.

In this work, we propose to study numerically a polyethylene (PE) membrane drilled with air holes following a triangular array, as illustrated in Figure 1. The structured membrane is characterized by three geometrical parameters, the thickness (h), the diameter of the hole (D) and the period of the array (P). In section II, we discuss the effect of structuration of the PE membrane in the Mid-IR range. In section III, we investigate the thermal properties of the photonic membrane to maintain the thermal comfort of the human body.

II. OPTICAL PROPERTIES

We performed the numerical calculation with the help of the Finite Element Method (FEM), considering an incident wave coming from the human body and launched in air medium normally to the photonic membrane. To simulate the interaction wave-photonic membrane, we used the commercial COMSOL software to solve the Maxwell equations. The elementary unit cell is defined Figure 1, where we applied the Periodic Boundary Conditions (PBC) along the two directions x and y to build the periodic membrane. We thus calculated the reflection (R) and transmission (T) coefficients and deducing the absorption coefficient (A) by the formula A = 1 -R -T. Figure 2(a) shows the evolution of the reflection R (black), transmission T (blue) and absorption A (red) in the wavelength range [5-15 μm] for a non-structured membrane of thickness h = 4 μm. The blue light shaded area corresponds to the human body radiation calculated at 34 °C following the Planck law. One can see that, for a thickness h = 4 μm, the transmission is comprised between 80% and 100% with an average absorption less than 10%. It means that the PE membrane is almost transparent in the Mid-IR. In order to show the effect of geometrical parameters on the photonic membrane spectrum (that could happen when using active polymer reacting to parameters, such as temperature or humidity), we homothetically increase the three parameters h, D and P. Figure 3 shows the spectrum for the set of geometrical parameters: h = 5.1 μm, D = 7.1 μm and P = 9 μm. One can see that the photonic effect has been shifted to higher wavelengths. With these chosen parameters, peaks and dips now occur in the vicinity of 9 μm. Therefore, a variation of the geometrical parameters offers the possibility to span the full range of radiation of the human body at the skin temperature 34 °C.

III. THERMAL PROPERTIES

We then investigated the thermal properties of the photonic membrane, considering an unidimensional heat model previously developed [START_REF] Tong | Infrared-Transparent Visible-Opaque Fabrics for Wearable Personal Thermal Management[END_REF]. The two volumes of control in our case are: the human body standing and relaxed and the PE membrane. The emissivity of the human body and environment is assumed to be equal to the unity. In the thermal model, we have considered all conduction, convection and radiative heat flows between the human body and the indoor room, through the photonic membrane. The resolution of the thermal equations leads to a balance where the temperatures depend on the scattering coefficients calculated in the previous part.

To estimate the efficiency of the photonic membranes we proceed to the calculation of the required ambient temperature to achieve the skin temperature of 34 °C. This latter is considered as a reference for a comfort feeling of the human body.

Figure 4 represents the evolution of the required ambient temperature as a function of different set of parameters of the photonic membrane. The blue curve corresponds to the ambient temperature for a non-structured membrane, drawn as a reference. For the structured one, we have considered different scaling factors, taking from reference [START_REF] Assaf | Polymer photonic crystal membrane for thermo-regulating textile[END_REF]: α1 (h = 4 μm, D = 5.5 μm, P = 7 μm), α3 (5.1 μm, 7.1 μm, 9 μm), α5 (6.3 μm,8.6 μm, 11 μm), α7 (7.4 μm, 10.2 μm, 13 μm) and α9 (8.6 μm, 11.8 μm, 15 μm). Figure 4 shows that for the nonstructured membrane with a thickness of 8.6 μm (α9), the comfort skin temperature of 34 °C can be reached with an ambient temperature of 25.5 °C. On the other hand, when the same membrane is drilled with air holes of diameters 11.8μm and a period of 15 μm, an ambient temperature of 25 °C is sufficient to achieve the skin comfort. It means that the latter structured membrane minimizes the necessary external temperature to maintain the human body in thermal comfort by almost 0.5 °C.

IV. CONCLUSION AND FUTURE WORK

In conclusion, we have demonstrated theoretically that a change in the structuration parameters of a polymer membrane can modulate the optical coefficient in the Mid-IR range. We show that, with an appropriate design of polymer photonic membrane, we can efficiently modulate the thermal radiation emitted from the human body. Compared to a regular PE textile, the photonic membrane maintains the thermal comfort of the human body with a lower ambient temperature of 0.5 °C. In addition, we seek to study photonic membranes based on active polymer, sensitive to ambient temperature, to study a textile membrane which acts both as a sensor and a passive actuator.

Figure 1 .

 1 Figure 1. 3D and top-view representation of the polymer photonic membrane. The red dotted lines represent the elementary unit cell.

Figure 2 (

 2 b) reports the same calculation of the coefficients when the membrane is structured with the set of geometrical parameters: h = 4 μm, D = 5.5 μm and P = 7 μm. The comparison between the spectrum of the simple membrane (a) and the structured one (b), shows the occurrence of new peaks and dips between 6 and 7 μm (see Figure2(c)). It means that the structuration clearly affects the scattering coefficients at low wavelength. The modulus of the calculated electric field shows that the two peaks (A and C) correspond to guided modes inside the membrane. With respect to the middle plane of the membrane, the first one (A) is antisymmetric while the second one (C) is symmetric. The peak B corresponds to a mode confined in the air hole. This latter gives rise to an asymmetric peak and comes from the interaction of the localized mode B with the incident wave, known as a Fano-like resonance.

Figure 2 .

 2 Figure 2. (a, b) Reflection (black), transmission (blue) and absorption (red) spectra for the (a) non structured and (b) structured PE membrane with the geometrical parameters: h = 4 µm, D = 5.5 µm and P = 7 µm. (c) Magnification of the reflection curve in (b) in the wavelength range [5-7] µm. Human body radiation at 34 °C is indicated by the shaded region. (d) Snapshots of the modulus of the electric field for the three peaks of reflection A, B and C.

Figure 3 .

 3 Figure 3. Reflection (black), transmission (blue) and absorption (red) spectra for the structured PE membrane with the geometrical parameters: h = 5.1 μm, D = 7.1 μm and P = 9 μm.

Figure 4 .

 4 Figure 4. Evolution of the required ambient temperature to achieve 34 °C as a function of geometrical parameters for a skin covered with a nonstructured (blue) and structured (red) membrane.

ACKNOWLEDGMENT

This work was supported by the European Interreg project 'Photonitex'.


Emmanuel Grolleau
email: grolleau@ensma.fr

Annie Choquet-Geniet

Off-Line Computation of Real-Time Schedules by Means of Petri nets

Keywords: Petri nets, earliest firing rule, real-time systems, off-line scheduling

We present an off-line methodology of analysis of real-time systems, composed of periodic, precedence and resource constrained real-time tasks. As there is no polynomial optimal scheduling technique for such tasks sets, we present an enumerative method based on the construction of the state graph of a Petri net. The time is modeled by the Petri net through the earliest firing rule.

1.

INTRODUCTION

Real-time systems, most of the time dedicated to process control, are characterized by temporal parameters, induced by the dynamic of the controlled process. We assume that these parameters are a priori known, i.e. we are only interested in deterministic real-time systems, since they are the only systems for which the respect of the temporal constraints can be guaranteed.

A real-time application is designed as a set of mostly periodic interacting tasks, with fixed temporal characteristics. Once the application is designed, and the functional correctness proven, the system must be temporally validated, i.e. the temporal correctness must be proven, which expresses that all the temporal constraints are met, provided an appropriate scheduling policy is used. Two approaches are usually considered in order to solve the scheduling problem. The on-line approach : a scheduling policy is implemented within the scheduler ; and the off-line approach : a schedule is stored in a table used by a dispatcher.

The scheduling algorithms used on-line are based on priorities, mostly derived from the temporal parameters (e.g. Rate Monotonic, Earliest Deadline, Least Laxity), and they are polynomial in time [START_REF] Leung | A note on preemptive scheduling of periodic real-time tasks[END_REF][START_REF] Liu | Scheduling algorithms for multiprogramming in real-time environment[END_REF](see [START_REF] Stankovic | Implications of classical scheduling results fo real-time systems[END_REF] for a survey). Under some specific assumptions (e.g. for Earliest Deadline, independent tasks or precedence constrained tasks), some of them are optimal in the following sense : a scheduling policy is said to be optimal if, for a given task system, either the policy computes a feasible1 schedule, or there is no feasible schedule of the task system. The scheduling problem becomes NP-hard [START_REF] Mok | Fundamental design problems of distributed systems for the hard real-time environment[END_REF] when shared resources are involved (e.g. shared memory or control terminal). The main difficulty comes from the duration of the blockage of a task requesting a resource. In order to analyze the schedulability of such a task system, the duration of each task is increased by the duration of the longest blockage it could suffer. In this case, we then only dispose of sufficient conditions of feasibility. Furthermore, the temporal parameters of the tasks may then become unrealistic, this implies that the more the number of task interactions by means of shared resources increases, the more the efficiency of feasibility tests of on-line schedulability decreases. A second difficulty comes from the lack of optimal on-line algorithms for task systems where critical resources are involved.

Off-line scheduling methodologies have been studied in order to validate highly constrained task systems. The methodologies are usually exponential in time, but can lead to a feasible schedule, provided such one exists. Those approaches are either exhaustive (enumeration techniques based on Petri net modeling [START_REF] Choquet-Geniet | Exhaustive computation of the scheduled task execution sequences of a real-time application[END_REF][START_REF] Grolleau | Ordonnancement temps réel hors-ligne optimal à l'aide de réseaux de Petri en environnement monoprocesseur et multiprocesseur[END_REF] or branch and bound techniques [START_REF] Xu | Scheduling processes with release times, deadlines, precedence, and exclusion relations[END_REF][START_REF] Baker | Sequencing with due-dates and early start times to minimize maximum tardiness[END_REF][START_REF] Bratley | Scheduling with earliest start and due date constraints on multiple machines[END_REF]), or stochastic (genetic algorithms, simulated annealing).

We present a methodology based on a fine modeling of a task system, and on the modeling of time by means of the earliest firing rule [START_REF] Starke | Some properties of timed nets under the earliest firing rule, Advances in Petri nets[END_REF]. We then present some properties of the obtained Petri net and of its state graph. Finally, we show how specific feasible schedules can be computed.

THE TASK MODEL

We deal only with periodic tasks. We suppose that sporadic tasks with hard deadlines are modeled by periodic servers, and that background scheduling is used on-line for non-periodic tasks with soft deadlines. Each periodic task τ i is characterized by four temporal parameters [START_REF] Liu | Scheduling algorithms for multiprogramming in real-time environment[END_REF]: -r i , its first release date -C i , its processor load, or its worst-case computation time on each release -D i , its relative deadline, the time by which τ i has to be computed relative to its last release -P i , its release period: τ i is released at the dates r i +kP i , k∈ N I .

Off line computation of real-time schedules by means of Petri nets

For short, we note τ i <r i ,C i ,D i ,P i >, and S={τ i <r i ,C i ,D i ,P i >} i=1..n denotes a task system. We suppose that min i=1..n {r i }=0. We denote r=max i=1..n {r i }. The tasks are said synchronous if r=0, and asynchronous if r>0.

Our aim is to compute an infinite schedule meeting all the deadlines of the tasks. Moreover, when interactions of tasks are involved (message passing and use of critical resources), the implied structural constraints (precedence constraints and mutual exclusion) must be respected.

Communications are modeled by one to one mailboxes, and by assumption, the emission rate to a mailbox is equal to the reception rate. The resources can be accessed either in write mode, or in read-only mode (i.e. several read-only accessed can occur simultaneously). Moreover, some parts of the tasks can be non-preemptible.

THE MODELING STEP

As the interactions of the tasks are complex, the expressiveness of a Petri net (PN) model is appropriate. Furthermore, operational semantic involving the time must be associated to the PN modeling the tasks system. We assume that a quantum of preemption is defined: a running task can be preempted by any pending task at each preemption point. Therefore, the scale used to express the time is given in terms of preemption points, and a preemptible task can be preempted each time unit.

3.1

The modeling of time

The earliest firing rule (EFR)

A PN obeys the EFR if each time a firing of transitions occurs, a maximal set of transitions simultaneously enabled fires: let I be the set of enabled transitions for a marking M (note that I is not a multiset, since a transition t cannot fire more than once in the same firing step). A maximal set of transitions simultaneously enabled I'⊆I is defined by: ∀t∈I \I', t is in conflict with some transitions of I' (i.e. the transitions of I are not in conflict, and any other enabled transition is in conflict with some transition of I' ).

A PN with the EFR has been shown to be equivalent to a timed PN at maximal speed [START_REF] Starke | Some properties of timed nets under the earliest firing rule, Advances in Petri nets[END_REF]. It behaves exactly like a timed PN at maximal speed where all the durations of the transitions are one, nevertheless, their implementation is easier. Furthermore, the expressiveness of PN with the EFR is equivalent to the expressiveness of a Turing machine, therefore it can model the whole set of interactions between tasks.

DISCRETE EVENT SYSTEMS: ANALYSIS AND CONTROL

The modeling of periodic actions

The Figure 1.a presents the basic PN component which models the periodicity of an elementary action e, occurring with period P e (with P e >1). The transition Clock is a source transition which is always enabled without any conflict. It follows that each time a maximal set of transitions is fired, the transition Clock is fired, producing a token in the place Time which acts like a local time marker. Thus, we then assimilate the firing of Clock to a time unit in our scale of time. As soon as Time holds P e tokens, the transition Release is fired (simultaneously with Clock which is always fired), so a token is produced in the place Active each P e units of time at the dates (k-1)P e for k∈ N I . Finally, as each time Active contains a token, the transition e is fired, the action e occurs at the dates kP e .

The same principle is used to model differed periodic action (first release date greater than 0). If the first release date of the action e is r e ≤P e +1, the model differs from the previous model only by the initial marking (see Figure 1.b), and if r e >P e +1, a place and a transition are added to the model (see Figure 1.c).

On Figure 1.c, the transition Wait is fired during the r e -P e -1 first units of time. Then the place Time needs P e units of time to enable Release, which is fired at the date r e -1, so e is fired for the first time at the date r e .

3.2

The complete model

The Figure 2. represents a Petri net modeling the task system S={τ 1 <r 1 =1,C 1 =2,D 1 =3,P 1 =4>, τ 2 <r 2 =0,C 2 =1,D 2 =2,P 2 =2>}. Two main parts compound the model : the clock system, and the task system.

3.2.1

The clock system

The clock system models the behavior of the time in paralleling the clock systems of section 3.1.2. The body of the tasks can be complex and is described in the next section, but remark that the Release i transition produces a token of color a (for activation) in Active i , and that when the task

Off line computation of real-time schedules by means of Petri nets

completes its execution, a b-token is produced in Active i . This token means that the task has completed its last execution before another one. This token allows the PN to forbid task reentrance. In addition, some constraints are used on the allowed markings in order to model the deadlines of the tasks.

=1,C 1 =2,D 1 =3,P 1 =4>, τ 2 <r 2 =0,C 2 =1,D 2 =2,P 2 =2>}
When Time 1 contains 4 tokens, the task τ 1 has been released for 3 time units, thus, it must have completed its execution (i.e. M(Active 1 )={b}). It follows that the deadline of τ 1 is met if and only if M(Time 1 )=4⇒M(Active 1 )={b} (i).

For the particular case of τ 2 whose deadline D 2 =P 2 , Time 2 cannot contain more than D 2 tokens. But as soon as M(Time 2 )=1, τ 2 is released, so it must have completed its last execution. It follows that τ 2 meets its deadline if and only if M(Time 2 )=1⇒M(Active 2 )={a,b} (ii). The constraints (i) and (ii) are called terminal constraints and a marking meeting these constraints corresponds to a state of the system where all deadlines are met. Thus, an infinite behavior of the Petri net where all the reached markings meet the terminal constraints corresponds to a behavior of the modeled system where all the deadlines are met. For a task τ i , the terminal constraints are given by: if

D i <P i , M(Time i )=D i +1⇒M(Active i )={b}, and if D i =P i ,

DISCRETE EVENT SYSTEMS: ANALYSIS AND CONTROL

M(Time i )=1⇒(M(Active i )={a,b} or M(Active i )={b}) (the last case covers the case where r i ≥P i ).

The task system

Each task body of duration C i of the tasks system is modeled by a series of C i transitions (note that a series of n≥3 transitions can be compressed into a series of 3 transitions), each of them using a common resource: the processor. It follows that one transition of the tasks can be fired at a time. Interactions between the tasks can be modeled in an usual way by mailbox places, and resource places (in exclusion mode or in read/write mode). The beginning of a non-preemptible part is modeled by the fact that the first transition of the part uses the processor but does not restitute it: the processor is liberated by the last transition of the non-preemptible component.

Since we focus on the sequence of actions, each component transition of τ i is labeled with τ i , and the other transitions are labeled with the empty word. It follows that the language of the PN where all the reached markings meet the terminal constraints (the center of the terminal language) is exactly the set of feasible conservative2 schedules for the modeled system. It must be noted that it exists some tasks system for which no feasible conservative schedule exist but some feasible non-conservative schedules exists. In order to obtain non-conservative schedules, a idle task is added to the PN model. This task handles the idle slots and extends the language to the nonconservative schedules. Thus the center of the terminal language is the whole set of feasible schedules for the modeled system: each word of this language (i.e. each path in the state graph) is a feasible schedule.

ANALYSIS OF THE SYSTEM

Since the length of each word is infinite, we have to show that each word w of the PN language can be written w a w c * (where * is the Kleene star). In the case of synchronous task systems, at the date 0, all the tasks are simultaneously released. One major period later P=lcm i=1..n {P i }, all the tasks are in the same state as at the date 0. It follows that in this case, the marking of the PN at the date P is the same as M 0 . Thus, in the state graph of the PN, M 0 is an home marking, and each word can be written w c * where |w c |=P ( |w| denotes the length of w).

Off line computation of real-time schedules by means of Petri nets

In the case of asynchronous task systems, we have shown in [START_REF] Grolleau | Ordonnancement temps réel hors-ligne optimal à l'aide de réseaux de Petri en environnement monoprocesseur et multiprocesseur[END_REF] that for all feasible schedule, a date t c can be computed, with t c ≤r+P. This date is unique for a task system, and the state of a system at the date t c is the same as at the date t c +P. It follows that each word can be written w a w c * where |w a |=t c ≤r+P and |w c |=P. Thus the state graph contains a marking at the depth t c which is an home marking.

In both cases, the depth of the state graph is bounded, and contains an home marking.

The state graph contains the entire set of feasible schedules, and it is possible to extract the optimal schedules for several criteria (based on the response time, the lateness or the reaction rate) on a selected set of tasks. This particular pattern allows us to extract, in a complexity linear in the size of the graph, a sub-graph containing the whole set of optimal schedules for a given criteria. As an example, in order to extract the schedules minimizing the average response time of τ i and τ j , each edge of the state graph corresponding to a termination of τ i or τ j is weighted by its corresponding response time (which is computed from the depth of the edge). The other edges are weighted by 0. The optimal schedules for the given criterion are the paths whose cost is minimal. Since each word is a permutation of another, the graph is a diamond, therefore the computational complexity of the shortest path search algorithm is linear in the size of the state graph.

The optimal schedules for the applied criterion are a sub-graph of the state graph, and the technique can be applied recursively on this sub-graph in order to obtain the optimal schedules for several criteria (e.g. best worst reaction rate for τ k ,…).

Note finally that the fact that a finite word w reaches only valid markings does not imply that it exists an infinite word in the center of the terminal language whose prefix is w. Thus, the construction of the state graph of the center of the terminal language implies backtracking (i.e. some nodes have to be given up). This phenomenon can be reduced thanks to optimization: a necessary condition for schedulability can be tested for each reached marking.

Several heuristics are used in order to reduce the (non polynomial) size of the state graph. One of them significantly reduces the graph in forbidding non necessary preemptions: two concurring parts of tasks, independent from each others cannot interleave. The main advantage of this heuristic is that it does not reduce the scheduling power of the model (i.e. if there exists a feasible schedule, then this heuristic let at least one schedule).

CONCLUSION

We present a Petri net with the earliest firing rule which models periodic real-time task systems. The center of its terminal language is exactly the set of all feasible schedules for the modeled system. Since the state graph is bounded, it can be constructed. We use several heuristics in order to reduce it without reducing the scheduling power of the model: in fact it is an optimal scheduler. In our knowledge, our method is the only off-line method dealing with asynchronous periodic tasks, complex communications through mailboxes, resources accessed in read-only or read/write mode, nonpreemptible parts. A tool based on this method, called PeNSMARTS for Petri Net Scheduling, Modeling & Analysis of Real-Time Systems, has been developed.

Figure 1 .

 1 Figure 1.(a) Petri net model for a periodic action e (b) e is differed by r e ≤P e +1 (c) e is differed by r e >P e +1.

Figure 2 .

 2 Figure 2. Petri net model for the task system S={τ 1 <r 1 =1,C 1 =2,D 1 =3,P 1 =4>,

A schedule where all tasks meet their deadlines.

A conservative schedule does not let the processor idle while some pending tasks are to process.


M El

-Hadj Mimoune
email: mimoune@ensma.fr

Y Ait-Ameur

G Pierra
email: pierra@ensma.fr

J C Potier
email: potier@ensma.fr

Integration of component descriptions in product data management systems

Keywords: Parts Library (PLib), PDM, data integration, meta-data, tracability, EXPRESS language

This paper addresses two fundamental aspects of concurrent engineering processes. It suggests the integration of component and product data. On the one hand, the Parts Library standard, denoted P-Lib, has been described for exchanging part libraries between CAD systems, which use a big amount of heterogeneous data related to components or parts. Its data model allows the capability to exchange complex data between library management systems : data schemas, queries, constraints, domains and methods are described in this P-Lib data model. On the other hand, Product Data Management systems, denoted PDM, have been defined, in the last decade, in order to manage thousands of heterogeneous data (CAD/CAM data, BoM etc.) related to products. Technical data management permits the management of the all-informational patrimony of a product starting from its design until its discharge.

Products are essentially composed of pre-existing components stored in component or part libraries. This paper presents the approach we developed to integrate component data and product data. This approach has been applied with the particular standardised P-Lib data model for representing components and a particular PDM system namely SmarTeam. It will allow the automatically storage of component data in a PDM and the easy referencing of these data in the products during their whole lifecycle.

Introduction

The growth, the heterogeneity, the security of data motivates the creation of information processing systems to facilitate heterogeneous products data management during their whole lifecycle (CAD-CAM Files, Quality folders, BoM etc.). These systems are named PDM (Product Data Management Systems). In a number of industrial fields, products are constituted with pre-existent components stored in component or parts libraries.

The capability to refer to component data from a PDM, in order to allow the use of PDM to represent and to manage product data in parallel with component data, permits to represent both product and component data in the same design environment. As a result of this referencing capability, the development and management costs would decrease.

Moreover, the possibility to refer to and to manipulate component knowledge and data as well as the reason for choosing this component in a given product facilitate the maintenance of those products when, for example failing components are to be replaced.

Two main approaches can be used for describing several data models. The first one, called multi-modelling approach, consists in describing several data models. Integration of these data models requires a translation from a data model to another. The second one is the metamodelling approach where each data model is a particular instance of a data meta model.

The multi-modelling approach may be used for representing product data models in PDM (it is the one followed in the STEP standard for example in the Application protocols). The meta model approach has been followed by P-Lib standard for representing components (or parts library) data model.

Therefore, the integration of both approaches is a crucial issue when addressing both product data and component data. So, the goal of this paper is to present an approach to integrate both component and product data and knowledge in a common framework.

In the context of our approach, component data models are defined by means of instances of the P-LIB data model, developed in the Parts Library ISO-13584 standard. The P-LIB model is a formal data model allowing to represent and to exchange part libraries.

Product data are represented in a particular PDM. For implementation purposes, we have chosen the SmarTeam PDM, developed by the Smart Solutions Company. So, the goal of our approach is the representation of P-LIB data in a PDM.

The integration of these models requires the description of a common language allowing to represent them. For this purpose, we have used the EXPRESS data modelling language and its graphical representation. This choice was motivated by the fact that this language allows the representation of all the knowledge categories related to both components and products.

So, our approach uses the EXPRESS language and its graphical representation as specification language for representing all the data models presented in this paper.

The approach we developed is a mixed (or hybrid) approach. Indeed it does not totally use a meta modelling nor a multi modelling approach. It uses the capabilities of both approaches and their ways of representation. It consists in representing the P-Lib data components in two different representation levels: the meta level representation for component families descriptions (component classes) and the hard encoded (or the direct representation) for representing data stored in tables. The first represents component families while the second represents the components themselves. So, some P-Lib descriptors are represented by the PDM objects (representation at the meta level) and the other entities representing tables are represented by the PDM tables (direct representation). This choice allows to use the capabilities of both the LMS (Library Management System) for selecting components and PDM for managing product data. Therefore, the PDM becomes capable to refer directly to the components data.

This paper is structured as follows. Next section presents an overview of the formal data modelling language EXPRESS and its associated graphical representation : EXPRESS-G.

Section 3 gives an overview of P-Lib data models and its specifications. The overview of a PDM systems and description of a particular PDM (SmarTeam) is presented in section 4. Finally, last section presents the integration approach of the P-Lib data model in the selected PDM system.

Overview of the EXPRESS language

Knowledge modelling and automatic data processing have a great importance in different kinds of engineering knowledge. Several formal representations are used to formalise these knowledge models among them, we can cite the NIAM method, OMT [START_REF] Runbaugh | Object oriented modelling and design[END_REF], UML [START_REF] Jacobson | The unified Software development process[END_REF] etc. These formalisms were developed to allow a real world modelling (a universe of discourse) by semantic entities.

The use of CAD/CAM systems in engineering domains has begot an earnest problem, which concerns data exchange and sharing between contractors and subcontractors. This situation is due to their use of heterogeneous systems. Moreover, several formats were developed to allow this exchange. Among the different developed standards we can quote the STEP (STandard for the Exchange of Product data model) international standard which has developed the EXPRESS formal data modelling language (ISO 10303 -11). The goal of this language definition is to allow data models description in order to exchange and to share data compliant with these models [START_REF] Bouazza | Le langage EXPRESS[END_REF]. Moreover, it defines an exchange format for any data model specified in EXPRESS.

In the following, we will focus on the EXPRESS language constructs necessary to understand this paper. More details on the EXPRESS language can be found in [START_REF] Bouazza | Le langage EXPRESS[END_REF] and [START_REF]Industrial automation systems and integration --Product data representation and exchange --Part 11: Description methods: The EXPRESS language reference manual[END_REF].

General structure and EXPRESS concepts

EXPRESS is an object oriented data modelling language handling the important characteristics of object oriented language like abstraction, encapsulation, modularity and hierarchy [START_REF] Booch | Object Oriented Design[END_REF].

In EXPRESS a data model is represented by a set of modules, called SCHEMAs. Each SCHEMA describes a set of entities, which represent the objects we want to model. Each entity is defined by a set of characteristics called attributes. Finally, each attribute has a data type where it takes its values. A SCHEMA may also contain a set of functions and procedures, which allow data coercion (integrity constraint) and derived attributes expressions (behavioural knowledge).

Entities represent, in the real world, objects that have physical existence (screw, bearing) or conceptual existences (address, course). In EXPRESS the entity represent a class of objects, which share common properties and behaviours. Inheritance between entities, representing structural knowledge, is allowed.

Attributes represent the properties which characterise an entity. They allow descriptive knowledge modelling. An attribute is defined by an identifier and a data type which can be simple (integer, real, character), structured (lists, sets, bags, arrays which are rigorously defined in EXPRESS), or user defined like in programming languages (C++; ADA etc.). Attributes can refer to entities (aggregation); i.e. attribute value can be an instance of this entity.

Three kinds of attributes are distinguished: Explicit attributes, Derived attributes and Inverse attributes.

Constraints: the EXPRESS language supplies the capability to describe constraint expressions. Constraints on data models are introduced by two different rules types: local rules which are applied on each entity instance separately , and global rules which are globally applied on several entity instances at the same time.

Local rules shall be checked against for each instance of a constrained entity. They are declared, at the same time as the attributes. Local rules are applied on the value domains of set of attributes.

Inheritance: An EXPRESS data model is composed of a great number of entities, which are connected by father/son relationship (is_a relationship). If an entity A is a subtype of another entity B then A contains the properties of A more its own properties. A inherits all its parent properties entity.

In EXPRESS the inheritance can be simple, when an entity inherit only one entity, or multiple when an entity inherits several entities at the same time.

EXPRESS-G

EXPRESS-G is the graphical representation of textual EXPRESS data models. It allows synthetic presentation of textual EXPRESS data models, which are hard to read by human being. The graphical representation permits to make a partial representation of the full data model. Moreover, this formalism may be used to design a data model in preliminary modelling stages. EXPRESS-G allows structural and descriptive data representation with a graphical annotation. This format helps to have a global view of a data model. It should be noted that a graphical model increases readability and comprehensibility.

We have used the EXPRESS-G to model both the meta-model of P-Lib and the multi-representation model of PDM (SmarTeam) to confront the integration of their different approaches. So, the EXPRESS-G representation allows us to make a sort of interface between the two systems that will allow us to use components data (P-Lib) in PDM systems. We have chosen this formalism instead presenting program sources that we have developed.

Example

To illustrate the EXPRESS representation we will present, in the following, an example of a simple EXPRESS data model. We take the example of the geometry. Circle and point are both geometric entities. The entity Point has the attributes X, Y, Z representing co-ordinates and the inverse attribute is_centre_of, which allows expressing the following constraint: a point can be a centre to the maximum of two circles. The entity Circle has the following attributes: centre, radius and perimeter. The last one is a derived attribute.

The textual data model of this example can be represented as follow: The representation of this example in EXPRESS-G is given on figure 1.

Figure 1 Example of EXPRESS-G model

Legend :

P-Lib : the parts libraries data model

The lifecycle of a product is a complex track. It requires different knowledge and involves several experts that work on the same product but with different perspectives and points of views.

The resulting process includes specification, design, manufacturing, and maintenance etc. [START_REF] Pierra | Intelligent electronic component catalogues for engineering and manufacturing[END_REF]. Those activities are essentially informational processes and need to be handled by models, documents, computers etc.

The Computer Aided Engineering (CAE) area studies computer systems that allow to support these processes [START_REF] Pierra | Modelling classes of prexisting components in a CIM perspective: The ISO 13584/ENV 400014 approach[END_REF]. These computer systems supply efficient tools and mechanisms to represent different knowledge categories and to make it available for each expert in the suited format.

Ideally, these systems should allow each expert to work on his own perspective and should ensure coordination and interaction between the narrows perspectives. Often, products to be designed are made of pre-existent technical objects [START_REF] Moranne | conception assistée par ordinateur d'ensembles mécanique avec recherche d'une bonne solution: le logiciel SICAM[END_REF]. It is the case for several domains of engineering such as electronic, mechanic etc. Hence, in such domain, a very significant part of design knowledge is related to components design. This knowledge corresponds to the capability to select a component, to evaluate its behaviours and to create different representations related to each discipline.

Entity representation label label

The goal of P-LIB-based digital catalogues is to allow exchange of component knowledge between suppliers and designers. These catalogues should be able to transmit both component characteristics and their representations. It also should include the various information element included in catalogues like figures, documents, tables etc.. Notice that, in practice, these catalogues are used by product designers to choose the components to be inserted in products.

In order to represent catalogues and component knowledge, the P-Lib data model has been described and standardised. The next sections give an overview of this data model. More details can be found in [START_REF] Pierra | Parts library: Logical resource: Logical model of supplier library[END_REF], [START_REF] Pierra | description: methodology for structuring parts families, ISO document[END_REF], [START_REF] Harrow | Parts library: overview and fundamental principles, ISO document[END_REF], [START_REF] Sardet | Formal Specification, Modelling and Exchange of components according to P-Lib, A case study[END_REF]

P-Lib architecture

The general architecture of P-Lib is shown on figure 2. Suppliers describe components they supply within library (suppliers library) according to the formal P-Lib data model defined in EXPRESS and documented in the ISO 13584-24 and ISO13584-42 [START_REF] Pierra | Parts library: Logical resource: Logical model of supplier library[END_REF], [START_REF] Pierra | description: methodology for structuring parts families, ISO document[END_REF]. Users recover these data and store them in their own libraries. The data contain at the same time the component descriptions (general models) ant their representations (functional models).

Figure 2 general Architecture of parts library

Library data are structured into classes according to the object-oriented paradigm. Three kinds of classes are considered in P-Lib:

General model classes enable library data suppliers to provide the definition of parts represented by a hierarchy of part family classes.

Functional model classes enable library data suppliers to provide various representations (e.g. Geometric, schematic, procurement data etc.) for these collections of parts.

Functional view classes enable the specification of the kind of representation provided in different functional model classes. *logical description provides a referencing mechanism between library data obtained from different suppliers and enables the user to obtain an understandable view of parts held in the library.

Fundamental principles

The international standard P-Lib is based on different principles [START_REF] Harrow | Parts library: overview and fundamental principles, ISO document[END_REF]:

-It separates the representation of information held in a parts library from the implementation methods used in data exchange.

-It separates information about the structure of a parts library from the information relating to the different representations of each part or part family which belongs to the parts library.

-It uses a formal data specification language, EXPRESS to specify information about the structure of a library.

-It permits the information about the different representations of each part or family of parts within the library to be specified by different standards. The information is referenced within the information specifying the structure of the library.

P-Lib specification

The P-Lib standard was developed to allow designers to recover component data together with their different representations. A designer can, thus, choose component based on the properties supplied in P-Lib. The selection process consists of the following stages:

the first stage is to choose a particular component family (component category), which corresponds to the desired functionality , -the object of the second stage is to choose, in the family, one or several accurate component instances which are adapted to the requirements expressed by the insertion context. Notice that this insertion context is usually a PDM or a CAD system.

the end of this process is to choose a component well defined which we can precisely identify. This method of selection enables us to define a design problem to be solved. This process allows interchangeability in a maintenance context for example.

The users can access to suppliers' libraries across the interfaces, which exist between each system and P-Lib models. In this manner designers can use component data in their CAD or PDM systems.

As it was stated previously P-Lib uses the EXPRESS language to model and formalise component data. These data are stored in EXPRESS exchange format it provides and are encoded in ASCII files.

Conclusion

In conclusion we can say that the P-Lib standard has provided an approach and information models to facilitate components data exchange and their sharing between suppliers and designers systems. It allows exchanging digital component catalogues which integrate the supplier knowledge on the components he/she supplies (intelligent catalogues).

The P-Lib data model is a meta-model, which allows intentional and extensional description of component catalogues for their exchange between heterogeneous systems. This model characters both the structure and the characteristics of components (structural and descriptive knowledge), and the mathematical relations existing between different characteristics (procedural knowledge).

Use of P-Lib component data in CAD systems is possible using the interface which have been defined between P-Lib data and CAD systems.

But such interfaces do not exist yet between P-Lib and PDM systems. This is the main motivation of our work.

Components are largely used in industry to design and manufacture new products. Companies use PDM systems (Product Data Management) to manage data related to the products they manufacture (CAD/CAM files, quality folders etc.). So, it is crucial to offer some capability to use component data defined in P-Lib in PDM systems.

PDM systems description

With the use of computers in more and more activities, a company needs to manage efficiently thousands of heterogeneous data created each year. These data are related to CAD/CAM files, Specification files, Numerical Command (NC) programs etc. Because of the big volume of information, of the various actors using this information and of the diversity of data processing tools, controlling this information generates several problems. Among these problems, we can cite:

incoherence between various document and file versions used by different actors in development phases, -delivery of incomplete manufacturing data for production, -delay between product manufacturing and the delivery technical document.

To address these problems and subject to control the various technical information, involved in product development, in production, in marketing and in logistical support of industrial product, a new data management method was developed: the Product Data Management. This field is subject to an active standardisation work: STEP (STandard for the Exchange of Product model data); CALS-CE that is an initiative of the American Department of Defence aiming at defining methods and tools to manage and exchange technical information related to weapon manufacturing.

Technical data

Technical data are data concerning product and process definition, which are used during the whole of product life. They include all the data that allow product description throughout its lifecycle. These data can be structured or not structured. They can have either electronic or hardcopy support. These data are necessary to identify and to describe state and configuration of a product, to manufacture a product, to control product evolution, to use and maintain the product.

These data are generated by different computer tools: CAD/CAM systems (Computer Aided Design/ manufacturing), CAE (Computer Aided Engineering), QFD (Quality Function Deployment) etc. and they are related to design, to engineering, to the manufacturing, to quality management, to the logistical support etc.

Technical data are associated with product during its whole lifecycle (starting from its design until its discharge). These data have particular characteristics. Each datum is associated to a particular computer system, which allows to interpret its content.

Lifecycle encompasses several phases. It includes the following: requirement definition, concept design, production, operation, maintenance and discharge.

PDM definition

A PDM is a system which allows to organise and to manage all the heterogeneous data described in the previous section. It also allows to give the right data to the right person and, to provide to everyone his/her own view of the project. A PDM manages technical data access, modification and sharing. It permits multiple access at the same datum and/or at the same time. It ensures interfacing between all computer systems used inside the company. The following figure shows existing interaction between PDM and various other systems. Figure 4 shows how a PDM manages various data relating to a product. This management is done at two levels [START_REF] Randoing | [END_REF]. each set of product data (content) is recorded in a container associated with meta data. A PDM stores the content and manages the container.

Container management: supports the BoM (Bills of Material). It encompasses two functions: description of element components (Object ID, attributes etc.), and composition links that exist between different elements (component/composite relation). The composition link, between the component object and the composite object, is defined as another object.

Content storage: is a storage system with a great capacity: the vault. Vault content represents for example the drafting files, pictures digitised by a scanner, ASCII files etc. Visualisation of such object is not be possible without the engines that generated them and without PDM viewer. Without these engines we can't interpret their content. These objects are called BLOB (Binary Large Object). Objects, which are put in the vault, are controlled by the PDM. Any creation or modification is submitted to the validation by an ECO number (Engineering Change Order).

SmarTeam: description and structure

For our experimentation, we used a particular PDM system supplied by Smart solution called SmarTeam.

SmarTeam is founded on the principle of objectoriented databases.

We used this tool for study any feasibility of integration of P-Lib in a PDM. In the following, we will outline the structure of SmarTeam this will help us to

PDM

present the solution we propose to achieve this integration.

The structure of SmarTeam database is based on the concept of a project that represents the main class of the database. This global structure is constituted by a set of parallel class hierarchies where the first hierarchy represents the main classes. This structure permits to access data easily because they are generally bound to the instances of a main class and one can reach them through objects of this class (by the Browser or by the associated Application Programming Interface API).

Classes

In SmarTeam data are regrouped in several hierarchies of classes that represent categories of objects and then support simple inheritance. These classes are hierarchised to permit simple inheritance. In SmarTeam classes are classified in the following manner:

a) The main class: as stated above, the structure of data is organised around a hierarchy of main classes that plays a particular role in the database. It represents described product(s). Instances of the main class are displayed when SmarTeam is launched. This class has links with the other classes. Via these links, the user can reach the other objects directly.

Example: we can put the class Projects in the main class. Instances of this class can be motors, or gearbox for example. Others objects, such as parts of motors or gearboxes, will have a link with the instances of the class Projects.

b) Super-classes: they are the higher level classes in the hierarchies of which the first described is the main class. They are used to regroup classes in a specialisation hierarchy, and they constitute a separate tree. To every Super-class, it is necessary to associate indexes that allows the system to verify the uniqueness of objects in the class and that play the primary key role in a database.

Super-classes permit the construction of link classes between all classes that are in the hierarchy. The link between two classes is an object of the link class that binds their super-classes. e) Internal classes: In SmarTeam, predefined classes are used by the system to manage the database. For example the identification of users (their names, passwords etc.) is recorded in the internal class USERS. The other classes are used for the management of documents (identification of applications that are applied to each type of file to permit its visualisation for example).

f) Link classes: we distinguish two types of links in SmarTeam: aggregation link and association link.

Aggregation (or composition) link classes: aggregation is an association between a parent object and one or several son objects. This type of link is used typically to bind an object with its components. For example a wheel is composed of a tire, of an air room and of a rim. We can associate to the wheel these components through the use of the composition link. The composition link classes are created automatically for every super-class. These classes permit to stock aggregation links between the different objects (the link composite-component between two objects is an object of the composition link class).

Association (or logical) link classes: SmarTeam permits to bind between two classes (an instance of these classes) without taking into account their place in the hierarchy. We can make this link by the association link classes. For example, we can bind a screw CHc10 that is an instance of screws class with a document describing this screw.

g) Lookup table classes: they contain a list of strings and they are used only to define an enumerated type of data for an attribute that can only take its values in this list.

The general structure of the described classes is illustrated by the EXPRESS-G diagram of figure 5.

Figure 5 : general structure of classes in SmarTeam

All classes have some predefined common attributes called class attribute. They allow the definition and the characterisation of classes (class_name, class_ID etc.). They take the same values for all class instances.

attributes

In object oriented paradigm, a class has a number of attributes that permit to distinguish objects in one class. In SmarTeam, these attributes, themselves, have a certain number of properties that distinguishes them from some others attributes. Figure 6 illustrates properties of attributes in SmarTeam. -obligatory attributes: are predefined attributes assigned with each class and their values are managed by the system.

-mechanism Attributes : there are two mechanisms in SmarTeam: file management and revision management.

The first one allows documentation management (in a file-managed class, each object is associated with a document and has file management attributes), the last one allows revision management and verification (register, checkin, checkout, approval etc.) -user defined Attributes.

objects

Objects are instances of classes. They differ from each other by their object identification id (OID) and by their attribute values. For example, for classes Screw and Drawing, a Screw CHc10 will be an object of class Screw, its representation would be an object "Draw_screw", instance of the Drawing class, and link between these two objects would be an object of the corresponding link class.

Objects have attributes of the class to which they belong (predefined attributes and attributes defined by the user). Values of predefined attributes are assigned directly by the system. Object_ID value is assigned by the system and it takes an unique value used by the system to identify the object in the database.

PDM specifications

PDM systems are used to manage heterogeneous data, which describe enterprise products (CAD files, Production Management System (PMS) data, BoM etc.). These data represent the static characteristics of products. Bill of Material (BoM) is the decomposition of a product in standard components purchased or in components manufactured in the enterprise from raw materials. It is well-known in mechanics and it is the point of departure of the PDM. In the PDM, at the physical components, the maps, the technical draws, the quality folders which allow the better description of the products, were appended. This decomposition is called METADATA. In the PDM the link between product and its components is an object of composition link class. So, both the OID of parent object (composite) and the child object (component) are stored in the link class. The same approach is used for the association links, which are used typically to link the physical components with their technical draws.

Conclusion

PDM systems are software developed in the last years to allow management of heterogeneous data, which describe products. These systems support products lifecycles including: requirement description, concept design, production, operation, logistical support, maintenance and discharge. They also permit quality management. This is very important to have ISO 9000 certificate to support concurrent engineering process. It is well known that using pre-existing components to design and to manufacture a new product is very useful. It allows to considerably decreasing prices of products. Pre-existing component data are recorded in a P-Lib's models manager. So, it is useful to reference directly from PDM component data. We will present the approach we developed to integrate P-Lib in a PDM system in the rest clause.

Integration approaches

Convergence and difference between PLib and PDMs

P-Lib describes component families by meta models. So, the data models, which hold the component (Physical files) are instances of the meta models. It has been defined so as to be easily extensible and to be very general. PDM systems describe products and manage BoM and documents which are related to these products. The modelling approach used in PDM is called the multimodelling approach, because a specific model is developed for each BoM. Each software editor chooses a model which fits with its needs. In STEP a generic PDM data model has been defined from which everyone can derive its own specific data. So, the main difference between both approaches is due to the representation levels. Meanwhile, both approaches are intended to describe technical components and products. This is the reason which lead us to study integration of P-Lib in a PDM.

Aims of integration

The aim of integration of P-Lib in PDMs is specially to allow designers manufacturers and users to benefit from the suppliers' knowledge on components, as it is embedded in electronic catalogues. This knowledge, described by suppliers on components, must be available for use by designers, manufacturers and users and workable by constructors. So, this integration should allow storage of P-Lib component data in a PDM and should provide referencing those data in product data, therefore an efficient maintenance of products.

Integration approaches

a) Direct representation: in the PDM, data are stored in tables where each line represents an object of the class represented by this table and each column represents values of an attribute. One needs model not only table content but also table schema. Instead, in P-Lib another approach has been developed to represent tables because this approach requires that the table schema are defined before population such table. This approach consists in representing them by a list of lists representing each attribute in a column of a table. So, tables are represented by a number of EXPRESS entities. Moreover, in P-lib models, the classes representing families of components and their properties are also represented separately (metarepresentation).

So, the direct representation consists in extracting component families from the meta model and in representing them by PDM objects. As stated before, component class properties are represented by separated entities in P-Lib. These entities contain a set of attributes that are common to all the instances. In SmarTeam class attributes are predefined, so to avoid the redundancy of data we have opted to represent the common attributes which describe a class by a description classes and to link the two classes. For example, for a Screw_family class we associate directly the object attributes: diameter, length etc. and then we create a class Screw_family_description that is associated with the Screw_family class. In SmarTeam dynamic creation of classes is not allowed, so this approach does not enable us to make an automated integration. b) Meta levels representation approach: this approach consists in representing each P-Lib entity, such as it is defined in the EXPRESS model and represented in an exchange file, by PDM objects. Every P-Lib entity will be represented as a class in the PDM. For example, each of the entities supplier, class, component class, functionnal view class, etc. will be represented by PDM objects. The weakness of this approach is the impossibility to represent, in SmarTeam, aggregate data types (used to encode P-Lib tables). It is also the complexity to browse and to query such a meta model. c) Hybrid or mixed representation approach: this approach consists in using both approaches in parallel. It allows us to benefit of the advantages of both approaches. We separate the representation of tables and the representation of classes. On the one hand, we represent tables that contain component attribute values by relational tables provided by the PDM (direct representation). On the other hand, classes such as supplier, class, component class, functionnal view class, and so on are represented by PDM objects (metarepresentation). In the meantime link classes will be created to link objects with tables that contain their attribute values.

This approach has been implemented on the Smarteam PDM system and several examples have been processed.

Figure 3 :

 3 Figure 3: class hierarchy in P-LibThe figure3summarises the description given above. It gives an overview of the whole P-Lib data model.These classes shall be defined as a dictionary. It consists of a set of entries associated with a humanreadable and computer-sensible representation of the meaning associated with each entity. This dictionary

Figure 4 :

 4 Figure 4: PDM systems interfacing with computer company systems.

c)

  Leaf classes: Leaf Classes are classes of the lower level in all parallel hierarchies. In SmarTeam objects are only instances of leaf classes. The other classes are not instanciable (super-classes and intermediate classes). d) Intermediate classes: intermediate classes are those classes that are between super-classes and leaf classes in the parallel class hierarchies. They permit common attribute factorisation. Both intermediate classes and super-classes are abstract classes.

Figure 6 :

 6 Figure 6: attribute properties SmarTeam distinguishes four types of attributes -class Attributes : are attributes that allows the definition of classes (CLASS_NAME, ID etc.) and they take the same values for every class instances.-obligatory attributes: are predefined attributes assigned with each class and their values are managed by the system.-mechanism Attributes : there are two mechanisms in SmarTeam: file management and revision management.

Summary and Conclusions

In this paper we presented the approaches we developed to integrate P-Lib defined component cataloguesin in to PDM system. We have discussed the possible approaches and we have proposed to merge two approaches: the direct representation and the meta level representation. The resulting approach is named hybrid or mixed approach. It allows us to represent in the same model P-Lib descriptors, which characterise component families and suppliers, and P-Lib entities representing tables by PDM relational tables. The advantage of this approach is the possibility to make a completely automated integration of P-Lib defined catalogue and to keep the specificity of P-Lib data model, which contains a complete description of component families. Notice that no changes on the PDM system are required. As a result, this integration will allow the use of a PDM systems to manage at the same time component and product data. It allows the easy recovery of any component data as well as the knowledge on these components from its reference. It will also allow the integration of LMS's (Library Management System) and PDM's functionalities. This integration leads to increasing the productivity and to simplification of the component selection and their referencing within products. It makes also easier products maintenance by making possible the automatic exchange of component referenced when some components become e.g. obsoletes.