Dr Julien Gueslin

"Inventing" the Latvian democracy in the Western Europe

Keywords:

    "Inventing" the Latvian democracy in the Western Europe: Anna Ķēniņa and the Latvian propaganda in the Swiss and French democracies in 1917-1918", CIGANOVS (J.),Democratic processes in the Eastern and Central Europe in 1917: political, military, social and cultural aspects",

Europe. This and the weakening of the Russian Empire forced the Western powers not to stay indifferent and to begin to collect informations and to have contacts about nationalities like Baltic nation whose recent history was almost unknown to the diplomats and the majority of the public opinions.

Until 1918, the Latvian emigrants played a fundamental role, being the one and only source of available and specific information. Considering the existing constraints in the fighting countries (specifically the censorship and the control of all external information), Switzerland represents an ideal place to publish information and advertise one's ideas. The emigrants are also the first interlocutors of the western diplomats, as they try to draw the attention of public opinion. They are also a main subject to this real and secret war of influence between the central powers and allied powers [START_REF] Elsig | Les shrapnels du mensonge: la Suisse face à la propaganda allemande de la Grande guerre, Antipodes[END_REF] . In the midst of an evolving conflict, each emigrant or political group has to position themselves, be it openly or secretly, and then assess the gains to be made while ensuring that they do not discredit themselves. The evolution of the case of Anna Kenin 2 ), due to her role as a Latvian publicist and intellectual abroad, is interesting to study from 1916 to 1918. She is indeed going to play an important role in France and in Switzerland in order to make her country better known.

As Nora Ikstena's book on Anna Kenin demonstrates, at that time the young Latvian intellectual has already had a rich and varied career path. Recognised as pedagogue and high school principal, she symbolizes the rise of the Latvian urban and intellectual bourgeoisie, who wants the country to progress politically and nationally and confront the German elites and the Russian bureaucracy 3 .

Coming from her family heritage and her activities, she has an income that enables her to travel abroad and study. She thus becomes familiar with Western thinking and innovations that she will introduce in the Latvian territories. After two years spent in Paris at the Sorbonne (1911-1913), she goes to study at Genève's Institut Jean-Jacques Rousseau, an institution that was then famous throughout Europe for its innovative educational methods [START_REF] Kenin | Archives of the Institut Jean-Jacques Rousseau (University of Genève)=AIJJR[END_REF] . This is where the war takes her by surprise. Unlike Rainis or the Lithuanian Juozas Gabrys, she has not made a name for herself abroad. She does not seem to have contributed to the activity of the circle of Latvian and Lithuanian intellectuals and students who benefited from the sympathy and interest of liberal French intellectuals (such as the historian Seignobos or the politician Painlevé) who defend in 1912 and 1913, the cause of the nationalities (and in particular those unknown at the time of the Russian Empire) in the framework of the magazine "Annales des Nationalités" 5 . But she decides to send an anonymous contribution to the "Journal de Geneve" in reaction to the pacifist manifesto published by the writer and future Nobel prize Romain Rolland "Au-dessus de la mêlée" (Above the Battle). Her contribution is published on October 12, 1914, and will be published again in 1915, following the text of Rolland in the book edited with the same title as this one 6 . Kenin presents extremely well the dilemma that she and a good part of the Latvians are facing. They are trapped between the threat of Pan-Germanism and Pan-Slavism and divided in Germany and Russia between admiration for the culture and spirit of the two great powers and the need to oppose imperialisms the threat, in case of victory, of increased oppression. Kenin chooses the Russian side at the beginning of the War because she fears the German Empire might play the German-Baltic opponents. She has also the hope that, unlike German intellectuals, the Russian liberal elites will keep a critical distance from the Russian autocratic regime. Given their degree of development, Latvian elites can thus hope to play a role and defend their interests in a renovated and democratized Russia. On the contrary, if the fate of Belgium had already moved and alerted Latvian public opinion, the conquest of Courland, and the German policy which was being implemented there, reinforced the sense that opposing Germany is necessary. Above all it also draws attention to the ideas and theories disseminated by Pan-German circles in the German press.

Finally, Anna Kenin, Francophile and Anglophile, hopes that the alliance with the Western powers will impact on the Russian regime and that the idea of a war in the service of the right of the peoples to Self-determination will have real repercussions on the fate of the peoples of the Russian Empire.

Anna Kenin is far from being representative of the tendencies of the Latvian circles in Switzerland, especially those of the social democrats who will keep their distance with her and will always criticize her propensity to look too much on the side of the Entente as well as her very nationalist positions. However she will always manage to deal with many Latvian (in particular Austra Osolin or at times with Rainis) to defend national identity and to oppose the efforts of German propaganda to get through the situation of the occupied Courland the attitude of Latvian public opinion. Latvian emigration is scattered in the different Swiss cities, and often at this time each one acts in a rather isolated way. In addition to Rainis in Lugano / Castagnola, we find Austra Osolin and Liepin in Basel (contributing to the Basler Nachrichten), Lokis Forel, the daughter-in-law of the famous Swiss psychiatrist Auguste Forel who writes in the "Lausanne Gazette" and makes her Father-in-law aware of the Latvian question, and last but not least Cielens and Fritz Reiss in Bern 7 .

In Genève, Anna Kenin, can rely on more networks of influences, which are also more diversified, in particular an environment of progressive Swiss intellectuals, teachers, connected to the Protestant community and concerned with the questions of the pacifism and the rights of the small nations. Among them, are the members of the Institute and society Jean-Jacques Rousseau: Pierre Bovet Director of the Institute and contributor to the pacifist newspaper « L'Essor », Edouard Claparède founder of the newspaper, holder of the chair of psychology of the University of Genève, Adolphe Ferrière, famous teacher, who will create in 1921 the international League "pour l'éducation nouvelle" for a new education and who, with the other two, is at the origin of the movement which is going to revolutionize in the next decades the educational ideas (in particular with Jean Piaget and Celestin Freinet) 8 . Most probably thanks to them, she meets Alexis Francois, a pastor's son, teacher of history of the French language at the University of Genève and chair of the Society Jean-Jacques Rousseau.

She is also meets the former Rector of the University Bernard Bouvier, cofounder of the society; of René Claparède, brother of Edouard, who is a leading Swiss figure of the fight in favor of the right of natives of the colonial Empires (chair of the Swiss League of defense of the natives ) and in favor of the nationalities (for example his action in favor of the

Norwegian independence ).

They all belong to well-known families of Genève's pastors and are often described by their contemporaries as passionate about social justice (often close to social Christianism) as the peoples, as well as the Ferrière. The uncle of Adolphe, Louis, a former pastor, will soon welcome Anna Kenin and Austra Osolin to give talks in his salon, and thus contribute to raise awareness of the Latvian for many members of Genève's elite, such as Auguste de Morsier, Paul Moriaud, professor of law and founder of the Association for the Protection of the Right of the People and of many professors and pastors of Genève. This is a truly intellectual environment made of idealists, who support the vision of a France fighting for the rights of small peoples, whose main function is to open for Kenin its networks and to support her efforts. In spite of her energy and her unfailing commitment, Kenin needs very much good « translators » willing to devote time and to use their intellectual authority at her service. As her wealth and the donations sent to her to pay for hers and her children keeping, decrease more and more as time passes, it is obvious that the financial support given to pay for scholarship fees or end difficult months is crucial [START_REF] Note About… | File " Third Trip in Russia[END_REF] .

In 1915, Kenin had witnessed with consternation the invasion of her country. Along with Rainis, she considered with interest for a short time to back up a project of Latvian-Lithuanian union proposed by the Lithuanians of Switzerland . One of the main promoters was Gabrys whose precious resources and the connections he had made with intellectual environments in Swiss or France, could prove useful for the Latvian propaganda. In August 1915, she took part in a Latvian-Lithuanian conference where, in the absence of Rainis, she gave a presentation on the situation of her country. Bur already at that time, in spite of a consensual resolution, divergences were great between those who wanted first to denounce German policy adopted in Courland (Kenin) or those concentrating their attacks on the tsarist regime and particularly the policy of « scorched earth » that lead to the evacuation in the worst conditions of hundreds of thousands of Lithuanians and Latvians. At that time , neither Rainis nor her had yet discovered the hidden agenda of Gabrys who moved from France to Switzerland because he was certain he had to play as much as possible the German card because of the total occupation of Lithuania . He thus secretly served the German propaganda in Switzerland hoping in return to influence the ideas and arise interest for the Empire to have a separated Lithuanian state in case of final victory [START_REF]Auf die Wache für die Nation[END_REF] .

The Latvian emigration, is busy counteracting, writing many publications to the many articles and brochures of the German press, published in Switzerland. This german publications present the German occupation under the best light and state that Latvians are favorable to the idea of an annexion or at least ready to acknowledge their fate will be more favorable in the future [START_REF] Broedrich-Kurmahlen | Das neue Ostland , Charlottenburg[END_REF] Ropp, pretending to be a Lithuanian citizen but in fact German agent who came to Switzerland). This statements are echoed by French press, which react sharply to this attack [START_REF]Befreiung oder Vergewaltigung ? Russland oder Deutschland[END_REF] .

The Congress of Nationalities organized by Gabrys and Von Ropp in Lausanne at the end of the month of June 1916 with German funds will create even more echoes. The congress is presented as an impartial manifestation dedicated to the problem of nationalities and thus attracts many Swiss intellectuals (e.g. Edouard Claparède or Auguste Forel). The organizers, as does Gabrys, while claiming their sympathy for the Allies, highlight in a clever way the communications hostile to the Russian Empire, or to the English and French colonial powers. These informations are widely communicated by German and Austro-Hungarian journalists that are present. Gabrys will prevent all speakers who wanted to condemn German policy, pretending agents provocateurs and Russian agents from Okhrana are present. If, according to Gabrys « own words », a Latvian agitator sent by the Russian embassy is thus silenced, he has to accept the speech of Anna Kenin 14 . In spite of the attempts to interrupt her, she protest again against the idea of a « liberation of Latvians by Germans », highlighting the heroic commitment of the Latvian people and its degree of culture, reaffirming the famous slogan of a free « Latvia in a free Russia ». She calls upon the allied to grant all their attention to the Baltic question: not having any illusion for the tsarist regime, she uses the ideas announced by the allied as a base for the democratization of the Russian Empire, in which Latvia would enjoy a wide autonomy [START_REF] Kenin | Le Peuple letton et la guerre[END_REF] . Focusing on the education level, the role of schools or agrarian cooperatives in the national Latvian movement she suggests without naming it the model of the third French Republic and the triumph of its republican bourgeoisie in the so called Republic « of the teachers ».

The Latvian press in Russia criticize the excess of passivity of Latvians and advocate for the necessity to have a more active propaganda. This is certainly the origin of the multiple contacts Anna Kenin and Austra Osolin start, in Genève, with the Swiss intellectuals. Some of them, as René Claparède, Auguste Forel or Louis Ferrière, pay even more attention as they had the feeling to have been instrumentalised by the conference on nationalities [START_REF] Doumergue | Claparède to Louis Ferrière[END_REF] .

In Genève, she meets by chance, professor Emile Doumergue, rector of the faculty of protestant theology of Montauban, international specialist of Calvin. He is the brother of Minister Gaston Doumergue, a politician future President of the French Republic. He had developed a strong interest for the cause of small nations (he had just published a brochure about Armeny severely criticizing Turkish policy) and he was firmly decided to build an idealized image of France being a long standing defender of the Right of small nations (and thus denounce German methods based on the use of Force).

Kenin made him aware with her alarming descriptions. He seems to have discovered with her a new publication by Rohrbach, one of the theoricians of pan-Germanism, in the review « Deutsche Politik » of Weimar. This bring about the inevitable disappearance of the Latvian nation and thus the interest of its connection to Germanism in the frame of a colonization policy.

He then decides to spend a month studying the Latvian question and write for Kenin an appeal meant to be published in the « Journal de Genève » in order to call attention on the « projects aiming to destroy » and fragment the Latvian nation 17 .

The text of the appeal is ready in November, and if it gets the support of most of the Swiss intellectuals, previously mentioned , yet many others are reluctant to support it, considering it is too engaged on a topic they know too little about. After also trying to get the support of German speaking Swiss citizens, a Swiss study committee is finally set up in Genève. At last, on February 13th 1917, the « Journal de Genève » publishes the appeal « An entire people exposed to a threat » under the signature of Alexis François 18 . Doumergue, then decides to write for French readers, an historical summary on the Latvian question with the help of Kenin.

From autumn 1916, the attention of French diplomacy is drawn to the actions of Anna Kenin. Since summer a great counterattack against German actions seems to be launched by Tsarist diplomacy. During December 1916, the deputy Zalitis travels to Scandinavia and England in order to condemn German policy and to highlight the resistance of Latvians and their loyalty to Russia. The journey of Tchakste to Scandinavia, Great-Britain and Russia is helped, but the 1917 revolution will stop him in Sweden [START_REF] Germanis | Von den baltischen…op[END_REF] . At the end of 1916, the Swiss trader Bibikov will also try to convince Kenin to accept the direction of a Latvian news agency in Switzerland, funded by grants of the Russian Embassy. According to Kenin, she declined the proposal because she did not want to depend on the Tsarist government as long as the Russian diplomacy stays shy to reveal "the actions of the Baltic barons". Had Alexandre Liepin not such restraints? In fact, the reports of the German Embassy in Bern accounts the growing activity of a Latvian news agency, a proof of the actions of Liepin and Osolin in Basle and Bern at the beginning of 1917. Numerous press releases and the publication of a bulletin (named "Pro Lettonia" in 1917) have widely circulated in the German speaking Swiss press. Kenin is also introduced to Emile Haguenin, head of the French propaganda in Switzerland, who will echo her activities in Paris 20 .

Kenin's position in Switzerland is difficult because of the attacks launched by other Latvian circles about her policy felt as too personal and also because of her strong temper. She did not spare others sensibility. She has also a great difference of point of view with the Social Democrats who condemn her policy as too personal and find her too well-inclined towards the Entente [START_REF] Ikstena | Letter from Lokis Forel-Upeneck to A. Forel[END_REF] . They support Latvian independence as a component of the international and revolutionary fight against imperialism. Among Latvian Socialists stays the hope of a rapprochement with the German folk and Social Democrats. The hope would be a common fight against Russian or German imperialism and the building of similar democracies. That idea seems reasonable because of the good understanding and the similarities of Latvian and German culture, intellectual activities and policies. Austra Osolin (who qualifies herself as close to socio-revolutionary thinking people and will always keep in touch with Kenin) asks Professor Auguste Forel to include references to the German nation and her lack of animosity towards Germans in the introduction she asked him to write for her. The title of her booklet written at the end of 1916 and published in 1917 reveals her state of mind: "Befreiung oder Vergewaltigung? Des lettischen Volkes Frage an das deutsche Volk". At the time when the call of the Swiss Comity is published in the Journal de Genève, the Latvian news agency and the editorial board of "Latvji Arzemes" (Cielens?) published a letter addressed to Wilson [START_REF] Osolin | [END_REF] .

There is no head-on opposition, but there are different orientations. Kenin has the will to separate distinctly imperial policy and German nation (a position she already defended in 1914). But there is also the judgement that solidarity with the German nation is not possible, at least on the basis of the political approach of Latvians. The reason why there is the need to play the game of the Entente.

It is 1917 that Kenin left Switzerland for France and England in order to convince the circles of the Entente to give their full support to the Latvian cause and help its propaganda.

Was it also connected with the journey of Tchakste and the organization of conferences? Or influenced by demands from the Russian Latvians to direct her action towards Anglo-Saxon countries? Was there the need for her to regain contact with specific Latvian groups? Or simply the need to find a job (as she has written it in a letter dated April 1917) or financial support, her incomings from Russia shrinking considerably? Her status stays difficult, because even with the advice of Ferrière to be opportunistic, her lack of support from the Russian Minister holds her back. The support of intellectuals as Seignobos allows her, after long months of efforts, to publish, at the beginning of 1917 summer, the study of Doumergue "Un petit peuple en souffrance. Les Lettons . Les provinces baltiques et le pangermanisme prussien en Russie" in a special issue of a Protestant magazine « Foi et Vie ». This magazine has a large audience on war problematics through its publications and through the conferences organized. It seems she went often to Montauban and Paris for proofreading of the book of Doumergue. Many details, references or statistics are her work. The many references of Doumergue to statements and letters of "a Latvian" are possibly related to Kenin. It also seems that she took of contact with the small Latvian community of Paris, notably with Aija Bertrand, the wife of Raymond Duncan and sister-inlaw of the well-known artist Isodora Duncan, who is working on a "Latvian library" and accommodates Kenin.

The prospects seemed better in London (where Kenin could expose her arguments and goals more freely, so Ferrière was thinking), but as the sources are very incomplete, there is no way to tell if her actions were successful. Her poor English prevented her to settle down in London for longer time 23 . As many Latvians, Kenin has probably hoped that the revolution of February would bring the democratization of the Empire as well as its complete autonomy. As we know, it was a great disappointment which induced growing exasperation. It is of interest to acknowledge that the new Russian government tried to reinforce its support to Latvian publishing, in order to counter German propaganda. Austra Osolin mentions in her letters to Forel in 1917 her sympathy with Kerensky'' political actions and her binds to his Minister for agriculture, Tchernoff, a SR who was her teacher at university. She feels able to accept financial support which will allow her to publish a new and improved issue of her booklet "Selbstbefreiung…" in 1917 24 . Before that, Forel and she had been introduced to Vladimir Victoroff-Toporoff, the new Director of the Russian news agency, and had accepted to collaborate at the writing of a special issue of the "Basler Nachrichten" (an issue dated May 26 th 1917, which was translated in French later on). That issue was financed by the Russian government and dedicated to the new Russian regime. Those articles written by Osolin and Forel will, afterwards, be published in a special booklet in both French and German: "Une Lettonie libre dans une Russie libre" 25 . Such financial support is not to be found towards Kenin, but thanks to Osolin and herself, the Swiss Committee still takes efficient actions. As when, April 1917, on behalf of Latvian information, Louis Ferrière, Alexis François and Auguste Forel write two letter addressed to the Swiss politician Robert Grimm. At that moment he was on his way to Russia to enquire about war end terms, they wanted to advise him against peace agreements that would be to the cost of small nations. May 1917, the Swiss Committee protests against an article published in a newspaper from Zürich in which a fake Latvian writes his support to the German policy.

The committee reveals that this article is in conflict with all other expressed points of view of different Latvian groups and especially that the last paragraph is the true replica of an article published in a German newspaper, so to say that the Swiss issue seems to be a hoax 26 .

In the period of autumn 1917, the fall of Riga clearly triggers a deep sense of dismay among Latvian circles in Switzerland. In a vibrant article published on September 15 th 1917 in the journal "La Semaine Littéraire", Alexis François pays tribute to Anna Kenin, "a hero of Latvia, a mother and a woman, but mostly an outstanding patriot", far away from her husband and children and on the verge of collapse. He also praised the tremendous courage and loyalty of the Latvian nationals "terribly disappointed" by the Russian "treason" 27 . As convincing the Alliance to further investigate the issue of Baltic provinces proves a daunting task, the sense of dismay keeps rising. As mentioned in an article inspired by the Swiss Committee and published in "le Journal de Genève" of November 6 th 1917, the question is to find out whether Latvia would become another Alsace-Lorraine or if Alsace-Lorraine is set to disappear altogether on both sides of Germany [START_REF]La Lettonie[END_REF] . This increasing focus, in particular from France, paradoxically stemmed from the October Revolution. The number of articles and stories on the key role of Latvian skirmishers during the military coup tarnished Latvia's image in Western countries, for a long time, and raised questions about a people that would have turned to bolshevism. On the other hand, the potential defection of the Russian ally, hence a potential concentration of German forces on the Western front, caused a serious crisis within French diplomacy. France then decided to call on all its possible networks within Russian empire and nationalist circles, seeking support and groups willing to maintain resistance to the German influence. In December 1917, an official unit is commissioned by the government to reshape the French policy towards Russia and to send as many missions and French nationals in Russia, in a bid to influence the Russian public opinion. The higher aim was to find alternative ways to slow down the German drive and counteract the prevailing sense of resignation. At the time, the main targets were Poland and Ukraine, considering that the Baltic States were either powerless to act or treated with caution [START_REF]Decision of Stephen Pichon to create a special Commission , 07.12[END_REF] . In this context, however, the following preventions from France started fading away. In a note dated November 26 th 1917, the Ministry of Foreign Affairs urges to start allowing all paper transfers from Switzerland's Latvian groups that are resisting the German influence. Detailed records must be drafted about the Baltic States that are "gaining importance while remaining completely ignored" 30 .

Another note from December 1917 mentions the fact that Anna Kenin "has joined the Russian office of La Maison de la Presse", the French propaganda services operating abroad 31 .

Without any of the department's archives left, however, we lack detailed information on Kenin's activities and on her final motivations. Kenin might have been then introduced in the house of Madame Menard-Dorian, where a number of intellectuals and liberal politicians supporting nationalities used to meet. This is where she may have met Philippe Berthelot, the powerful director of La Maison de la Presse and soon-to-be Secretary General of the Ministry, who will shape the entire French foreign policy as of 1918 [START_REF]and about Berthelot and Kenine: Letter from Albert Thomas to Berthelot (15.04.1921) and[END_REF] .

Kenin's first mission, along with Lithuanian national Milosz, is to monitor the entire international press, with particular focus on German and Russian media, before having articles translated and summarized for the French diplomatic community as well as for the press release given to French media. These records, that have been kept, are a huge source of information enabling the diplomatic community and the French public to better understand the situation in Latvia and, most importantly, the policy led by Germany in this country 33 .

Settled in Paris, Anna Kenin has privileged access to information and press bodies. As such, she becomes one of the most informed persons on foreign events, while many French people can only access uncensored authorised information.

She is able to expand her networks and meet new people. She meets for instance Albert Thomas, a former minister and a socialist politician with a keen interest in Russia and nationality issues, who traveled to Russia on several occasions in 1917. She helps him plan a third trip that will eventually not take place, but at this time, the man grows very attached to Latvia and supports many Latvian actions in France, in particular in 1918 and 1919. He promotes the funding of a mission to send Kenin to Switzerland and organize in Genève an event against the integration of Baltic States into the German empire. This mission would hinder the German policy on neutral States and compromise negotiations with the Bolshevik power. Kenin also aims at rebuilding ties with Lithuanian nationals, among which Gabrys, and bring him back closer to the Allies 34 . Back to Switzerland in Juanuary 1918, Kenin meets the Swiss Committee and coordinates a large people's assembly in the "Salle de la Réformation" in Geneve, gathering several hundreds of persons and drawing the attention of countless journalists from the country and abroad. The meeting comes under the spotlight as Germany's grip over Latvian territories is endorsed in the Brest-Litovsk Treaty at this time. For Latvian people, it comes as the first large event solely dedicated to their country organized outside of Russia. For the occasion, a booklet "Latvia against the German threat" is printed and handed out. It features articles of Pierre Bovet and Alexis François, the Swiss Committee's manifesto, Kenin's report on the nationalities conference, as well as several texts from Osolin. All the event's speeches are also published in a booklet in June 1918. This successful event is followed very closely by the German services which acknowledge the event's success but promptly start suspecting the French embassy of having funded the event planning and the various publications. Swiss people, however, will keep mentioning this "unforgettable event" of 1918 during all the 1920's League of Nations'meetings and events organized to honor Latvia and the Latvian delegations 35 .

Back to Paris, Kenin remains active and organises events focused on Latvia (such as a "Latvian day" at the Académie Raymond Duncaun on March 15 th 1918). Alongside Milosz and another Latvian national, Toupine, she creates "La Revue Baltique", a journal supported by all the French intellectuals with an interest in Baltic States. At the end of the war, the journal aims at informing the French public on the situation of these countries.

In the summer of 1918, Kenin is sent to Stockholm for a French propaganda mission and gets back to Paris the following year as a member of a French propaganda delegation [START_REF] Millet | Le sacrifice des Lettons (Speech during the Latvian Morning organized by Raymond Duncan at the[END_REF] . Thanks to her French network, she contributes to improving the two countries' relations in the intellectual and political fields. France supports Latvian democracy and decides the de jure recognition of the country in 1920. Kenin's actions are not, however, the main focus of this paper 37 .

Considering the huge political issues and the importance of events in Russia and Latvia at this time, the role played by Anna Kenin can seem somewhat limited: what could be the impact of a limited number of articles and events, even if marked with a deep sensitivity for the political situation of the Latvian nation? This true informal diplomacy and hidden work to influence western public opinion can nonetheless be acknowledged. The point is to fully understand where the Latvian nation started: completely ignored by the West, even the country's most limited claims were far from obvious, unlike that of other eastern and central European countries. With eyes turned on the German and Russian empires, where stereotypes prevailed, nobody (except a few intellectuals) would see the Latvian democracy as a possible or even desired option. Kenin and other Latvian nationals have rightfully proved deeply pragmatic and determined to use any opportunity to raise awareness on the Latvian society during the power struggles among leading countries. They may have avoided mentioning political and social interference to give an ideal image, but they did bring to light the sense of national awakening arising since the 19 th Century. The issue of how democracy could have been implemented even as a mere self-governance system, has never been addressed extensively in the texts dedicated to democracy as a political regime. A few implicit references can be found when reading about support to the Swiss democracy or the will to turn Latvia into "the Switzerland of Russia". Anna Kenin brought awareness in the West on the presence of educated circles and a literate people engaging in cooperatives and associations, as well as on the growth of print media in the country. She wanted, as a result, to introduce the idea of a politically mature people, matching all the official conditions deemed necessary to implement a solid democracy. More importantly, she showed how farmers and educated circles shared the common will to get rid of the terrible feudal system that prevented society and the country to develop freely. This consideration presented to the French public will also be one of the cornerstones of the Baltic propaganda, at the beginning of the independence period. Her attempt to prove that this feudal system is linked to a destructive German imperialism where power outweighs the law is a clear hint at the French revolution story, the basis of the Republican ideology at the time. The idea of a fight for the law is a clear link to the French thesis spread in 1917. This surely reflected the ideals of certain intellectual circles in Latvia but not the whole Latvian people, offering to foreign countries a streamlined version of events and motivations of other groups, in particular German-Baltic circles. The efforts also show how a generation of Latvian nationals acquired a strong European feeling through their studies and journeys in Western countries at the start of the century. This generation naturally got closer to Western educated middle-class circles with common ideals. The Latvian people proved skillful using ideas and standards to raise interest for their country, thus making it a part of democratic Europe in the Western minds.

July 2017

  . The pangermanist organs or brochures evoke the idea of a colonization or a progressive germanisation of the Latvian population. The declaration of the German Chancellor, on April 5th 1916 marks a turning point by making official the will of the Empire to annex Courland and therefore provoke a partition of the latvian territory. A Latvian comity chaired by Rainis is set up at the beginning of 1916 mainly to protest against the German plans of annexion, in the Swiss and Western press. They also want to react against what they see as German propaganda maneuvers aiming to circulate the point of view of so called Latvians in favor of the German proposals 12 . Latvian emigrates have found attention with the Swiss press, though their publications have little echo with diplomats or allied press until spring 1916, when German propaganda's intention of countering the image of the Entente defending nationalities becomes evident, communicating on her weak point: the alliance with a Tsarist Russia whose goal would also be « to exterminate nationalities ». A telegram sent in may 1916 to president Wilson by an alleged "league" of the "oppressed" nations of the Russian Empire requesting his help is published in two Swedish newspapers. This provokes the wrath of the Russian opinion and attracts the attention of the foreign press. The adhesion of an alleged group of the Latvians of Switzerland to this manifesto gives rises to a firm denial of the Latvian comity, advocating of his wide representation face to what would be the action of a few « Baltic-Germans » in the service of Germany (e.g. Silvio Broedrich, author of « Das neue Ostland » or the baron von


Michel Leclère
email: leclere@lirmm.fr

Nicolas Moreau
email: moreau@lirmm.fr

Query-answering CG Knowledge Bases ⋆

Conceptual graphs are a good choice for constructing and exploiting a knowledge base. In several of our projects (semantic portal for e-tourism, exploitation of digital object corpus, etc.), we have to query such bases. So it is natural to consider queries and bases as simple graphs and to compute the set of all projections from a query to a base. However, there is a problem of the return of this set of projections to the user. More generally, the main issue is about the definition of the notion of answers in an query-answering system made of knowledge bases formalized by graphs (Conceptual Graphs, RDF (Resource Description Framework) , Topic Maps, etc.). In this paper, we study several notions of answers and some of their characterizations. We distinguish between notions of answers by subgraphs of the base and answers by creation of result graphs. For the last type of answers, we define completeness, non-redundancy and minimality criteria of the answer sets and propose several notions of answers w.r.t these criteria.

Introduction

Many knowledge applications involve the elaboration and use of knowledge bases. Some examples are document management, digital object corpus management, enterprise knowledge repositories, construction of semantic portals, teaching aid management, the semantic web, etc. Two general contexts for using such bases can be noted, whereby use of these bases presupposes a query Q specifying the knowledge to be searched:

-Annotation context: resources are annotated by "descriptions" characterizing it; in this case, the exploitation is based on a search of resources whose annotations contain specific knowledge (e.g. [START_REF] Hollink | Semantic annotation of image collections[END_REF][START_REF] Moreau | Formal and graphical annotations for digital objects[END_REF][START_REF] Dieng-Kuntz | Conceptual Graphs for Semantic Web Applications[END_REF]). This type of exploitation only requires a definition of a deduction notion allowing selection of descriptions D (and thus the resources R linked to these descriptions) which are deductions of the searched knowledge Q. The set of answers to a query Q on an annotation base B is {R | (R, D) ∈ B ∧ D |= Q}; -Knowledge base context: some unstructured data that comply with a formal vocabulary defined by an ontology are stored in a base of assertions [START_REF] Fensel | Ontobroker: Or How to Enable Intelligent Access to the WWW[END_REF];

a querying system allows extraction of knowledge from the base (moreover, this type of exploitation could be used in the annotation context, considering descriptions of a subset of resources). This type of exploitation also needs a deduction notion to characterize the existence of an answer, but it also requires a definition of what should be returned to a query Q on such a knowledge base.

In this paper, we propose a preliminary answer to this question in the framework of knowledge bases formalized by conceptual graphs [START_REF] Sowa | Conceptual Structures: Information Processing in Mind and Machine[END_REF]. The long-term goal of this work is to define a query language for conceptual graphs and to implant it as a knowledge server over the CoGITaNT framework [START_REF] Genest | A platform allowing typed nested graphes: How cogito became cogitant[END_REF]. This first approach is a study of different notions of answers constructed from projections of a query graph Q to a graph base B.

In a knowledge base querying system with a formal semantic, answers are built upon "pre-answers" that are logical consequences of the base proving the existence of answers. A query is often composed of two parts: an head which specifies how answers are constructed from the "pre-answers", and a body which details how to select these "pre-answers". In the case of a base only made of conjunctive assertions, these "pre-answers" are the "smallest parts" of the base which has the body of the query as a logical consequence.

In this work, we only consider such simple bases (i.e. without rules) formalized by conceptual graphs [START_REF] Chein | Conceptual Graphs: Fundamental Notions[END_REF], although our results could be directly applied to other labeled graph formalisms, particularly to RDF/S knowledge bases of the semantic web [START_REF] Hayes | RDF Semantics[END_REF] (cf. [START_REF] Baget | Rdf entailment as a graph homomorphism[END_REF] for an equivalence of the two formalisms).

Unlike relational databases, these formalisms allow the introduction of an order relation over relations permitting the representation of a simple ontology and, more importantly, the use of variables in the base. In the querying mechanism, this leads to the problem of "pre-answer" equivalence and thus the problem of the definition of the answer notion.

We consider queries whose body is a conceptual graph and focus on the definition of several "pre-answer" notions. The main goal of this preliminary work is to study redundancy problems of these "pre-answers" which arise regardless of following operations applied to these "pre-answers" (e.g. specifyingthe concepts to keep by a lambda, or constructing a new graph with these answers).

As far as we know, this topic has not yet been studied. Several proposals have been made on querying relational databases with conceptual graphs [START_REF] Sowa | Conceptual graphs for a data base interface[END_REF][START_REF] Boksenbaum | Conceptual graphs for relational databases[END_REF][START_REF] Haemmerlé | Interfacing a relational databases using conceptual graphs[END_REF]. Many studies have been conducted in an annotation context (e.g. [START_REF] Genest | A content-search information retrieval process based on conceptual graphs[END_REF][START_REF] Moreau | Formal and graphical annotations for digital objects[END_REF]). An adaptation of relational algebra to the context of conceptual graph knowledge bases has been studied by S. Coulondre [START_REF] Coulondre | Cg-sql: A front-end language for conceptual graph knowledge bases[END_REF]. The relational bias limits answers to tuples of individuals over which several relational algebra operators are used (moreover, this author did not seem to consider variable-free knowledge bases). The most similar works were carried out by C. Gutierrez et al. [START_REF] Gutierrez | Foundations of semantic web databases[END_REF], who studied querying of knowledge bases of the semantic web formalized by RDF/S, but the set of "pre-answers" is not fully detailed, particularly the problem of answer redundancies.

The following section briefly introduces the main notions of the conceptual graph formalism upon which our work is based. Section 3 defines the querying model. Section 4 proposes several notions of answers and answer criteria based on the answers redundancy problem. Finally, the conclusion proposes some ideas for other types of answers.

SG formalism

The CG formalism we use in this paper has been developed at LIRMM over the last 15 years [START_REF] Chein | Conceptual Graphs: Fundamental Notions[END_REF]. The main difference with respect to the initial general model of Sowa [START_REF] Sowa | Conceptual Structures: Information Processing in Mind and Machine[END_REF] is that only representation primitives allowing graph-based reasoning are accepted. Several extensions that preserve this link with graph theory have been introduced (rules, constraints, conjunctive types, nested graphs, etc.), however, for the sake of clarity and presentation, we only present the simplest model in this paper.

Simple graphs (SGs) are built upon a support, which is a structure S = (T C , T R , I, σ) where T C is the set of concept types, T R is the set of relations with any arity (arity is the number of arguments of the relation). T C and T R are partially ordered sets. The partial order represents a specialization relation ( t ′ ≤ t is read as "t ′ is a specialization of t"). I is a set of individual markers. The mapping σ assigns a signature to each relation specifying its arity and the maximal type for each of its arguments.

SGs are labeled bipartite graphs denoted by

G = (C G , R G , E G , l G )
where C G and R G are the concept and relation node sets respectively, E G is the set of edges and l G is the mapping labeling nodes and edges. Concept nodes are labeled by a couple t : m where t is a concept type and m is a marker. If the node represents an unspecified entity, its marker is the generic marker, denoted * , and the node is called a generic node, otherwise its marker is an element of I, and the node is called an individual node. Relation nodes are labeled by a relation r and, if n is the arity of r, it is incidental to n totally ordered edges.

A graph

G = (C G , R G , E G , l G ) is consistent w.r.t. a support S = (T C , T R , I, σ) if :
the labels of the concept nodes (resp. relation nodes) belong to (T C ×(I∪{ * }))

(resp. T R ); -the relation nodes satisfy their signatures defined by σ.

for each individual marker i of G, types of concept nodes with this marker have a greatest lower bound. This condition can differ if one considers a conformity relation in the support, if one imposes a lattice structure to the ordered set of concept types, if banned types are considered (a disjointness type axiom), etc.

A specialization/generalization relation corresponding to a deduction notion is defined over SGs and can be easily characterized by a graph homomorphism called projection. When there is a projection π from G to H, H is considered to be more specialized than G, denoted H ≤ G. More specifically, a projection π from G to H is a mapping from C G to C H and from R G to R H , which preserves edges (if there is an edge numbered i between r and c in G then there is an edge numbered i between π(r) and π(c) in H) and may specialize labels (by observing type orders and allow substitution of a generic marker by an individual one).

Conceptual graphs are provided with a first-order-logic semantics, defined by a mapping denoted Φ.

The fundamental result of projection soundness and completeness establishes the equivalence between projection and deduction on formulas assigned to SGs: given two SGs G and H on a support S, there is a projection from G to H if and only if Φ(G) can be deduced from Φ(H) and Φ(S). Completeness is obtained up to a condition on H: H has to be in a normal form, so any individual marker must appear at most once in it (i.e. a specific entity cannot be represented by two nodes). An SG consistent w.r.t. a support can be easily normalized by joining concept nodes with a same individual marker. The normal form of a consistent graph G is denoted norm(G).

Two notions of equivalence can be defined over SGs: a syntactic equivalence, and a semantic one. The syntactic equivalence is characterized by the existence of an isomorphism between two graphs (which is a bijective mapping from nodes of one of the graphs to nodes of the other preserving edges and without label specialization). The semantic equivalence is characterized by the existence of a projection from the first graph to the normal form of the second, and from the second to the normal form of the first and corresponds to a logic equivalence between formula associated with graphs:

Φ(S) |= Φ(G) ↔ Φ(H) iff there is a projection from G to norm(H) and a projection from H to norm(G) (denoted G ≡ H).
This equivalence relation defines classes of equivalent SGs. SGs in figure 1 are from the same equivalence class. In each class, some graphs contain useless knowledge repetitions (redundancies) and there is a sole smallest graph with no redundancy, called the irredundant graph of the class (cf. [START_REF] Mugnier | Polynomial algorithms for projection and matching[END_REF]). A graph that is not in normal form contains redundancies (if two concept nodes have the same individual marker).

A subSG

H = (C H , R H , E H , l H ) of an SG G = (C G , R G , E G , l G ) is an SG, where : -C H ⊆ C G and R H ⊆ R G -E H is a restriction of E G to elements of C H × R H -l H is a restriction of l G to elements of H.
A strict sub-SG of G is a sub-SG with a strictly inferior number of nodes.

Characterization : An SG is said to be redundant if it is not in normal form or if it is equivalent to one of its strict sub-SGs. Otherwise, it is said to be irredundant1 .

Property : [START_REF] Mugnier | Polynomial algorithms for projection and matching[END_REF] An equivalence class contains one and only one irredundant SG, which is the graph (single up to isomorphism) with the smallest set of nodes.

An algorithm to compute the irredundant form of an SG, whose complexity is polynomially related to the complexity of the projection algorithm, has been described in [START_REF] Mugnier | On generalization/specialization for conceptual graphs[END_REF].

Studied querying model

The chosen context is a knowledge base composed of assertions of entity existences and relations over these entities, called facts, and stored in a single graph (not necessarily connected) consistent w.r.t. a given support. A support can be seen as a basic ontology. This framework does not put forward hypotheses on how facts have been collected and does not prohibit the existence of metadata (date, etc.) on facts composing the base (e.g. a selection mechanism of facts to be queried based on metadata). The only important hypothesis put forward is that all of the facts of the base to be queried are consistent relative to each other (with respect to individual markers) and consistent w.r.t. the support. Figure 1(a) presents the support used in the following examples of the paper. The SG base is assumed to be normalized. The base can be redundant because the irredundancy of the base does not solve the problem of answer redundancies, and computation of the irredundant form is expensive as the base can be large. Computation of the normal form is linear in the size of the base. Moreover, it is easy to write an incremental algorithm (called for each addition of knowledge in the base and whose complexity depends only on the size of the addition) for the normalization, whereas it seems difficult to find such an efficient algorithm for computation of the irredundant form.

From propositions of querying languages proposed for such knowledge base (e.g. SPARQL [START_REF] Prud'hommeaux | SPARQL Query Language for RDF[END_REF]), their definitions are clearly based on several mechanisms: 1. Adaptation of the base to the query, which consists of computing a base D ′ from a base D by application of a set of updating operations P (e.g. rule applications). 2. Selection of relevant parts of the base that respond to the query. This selection is made of "patterns" which specify selection criteria of base parts useful for contruction of the answer. These patterns have the same formalism as the base or indirectly of the same formalism because of the addition of variables. Thus these patterns are used like filters to select relevant base parts.

Verification of properties allowing to impose complementary selection criteria

differing from a simple assertion of relations between entities : path existence, constraints (not present in the representation language) on the entity linked to a variable. 4. Construction of an answer from these parts, which is a specification of the type of answer to return (tuples of values associated with query variables, a graph built from all parts, the number of answers, etc.).

The second point is the core of the querying mechanism. Constructing a query boils down to making assertions with unknown values (variables) which is information to be retrieved. When the formalism allows the introduction of variables in the base, it is important to know what to do when these variables are linked with query variables.

In our formalism, the selection criterion is a given SG Q, called the query SG. There is no constraint on the query (in terms of relevance, normalization or irredundancy). However, it seems natural to verify the consistency of the query w.r.t. the support of the base to avoid queries with no links to the base. One can consider to compute the irredundant form of the query as the size of the query is generally small. One can consider an unconnected query as several queries.

Therefore as one considers formalisms provided with a formal semantic, one can define "relevant parts" as "the smallest subgraphs" of the base whose query graph is a logical consequence; such subgraphs are called pre-answers in [START_REF] Gutierrez | Foundations of semantic web databases[END_REF]. In conceptual graph formalism, the existence of an answer is directly linked with the existence of a projection and a pre-answer is just the query image of a projection.

Definition 1 (Proofs of answers). Let B be an SG base and Q an SG query, a proof of answer is a projection π from Q to B. The set of proofs of answers from

Q to B is denoted Π(Q, B): Π(Q, B) = {π i | π i : Q -→ B is a projection}.
Definition 2 (Images of proofs). An image of a proof (or pre-answer), denoted π(Q), is a sub-SG of B, image of the proof of answer π from Q to B. The images of proofs sequence from a query Q to a base B, denoted

IP (Q, B), is IP (Q, B) = π 1 (Q), ..., π n (Q) , where n is the size of Π(Q, B).
All examples of the paper are from base and query of figure 2. Base is the SG of the figure 1(d). There are six projections of the query to the base, and thus six images of proofs. We have named some vertices (c 1 , r 2 , etc.) of graphs to refer directly to one vertex or to distinguish different subgraphs (see figure 3). Therefore answers are based on images of proofs, one may have to return the same subgraph of B several times. In the example of figure 2, projections π i = {(c a , c 1 ), (r b , r 2 ), (c b , c 3 ), (r c , r 3 ), (c c , c 4 )} and π j = {(c a , c 1 ), (r b , r 3 ), (c b , c 4 ), (r c , r 2 ), (c c , c 3 )} define the same subgraph (R 5 on figure 3). One can choose two ways to solve this problem:

-Considering it as the same answer (several proofs for the answer) -Differentiating answers by representing the projection in answer graphs (e.g. by adding id of query vertices to their images vertices in answers).

We consider only the first case, as we want to express answers in the same language (structure and vocabulary) as the base and query.

Different notions of answers

In this section we study several kinds of answers. The first type of notion is to keep base subgraphs, similary to images of proofs.

Answering by base subgraphs

The most basic answer that can be returned is the set of images of proofs.

Definition 3 (Answer by image subgraphs). The set of images of proofs of a query

Q in a base B, noted R IP (Q, B), is R IP (Q, B) = {π(Q) | π ∈ Π(Q, B)}.
This answer notion can be used to select exploration start points of the base (by focusing a subgraph of B), to explore the base or to be a first step of baseupdating queries. Figure 3 shows all of the five subgraphs answering the query.

Answering by base-independent graphs

In many cases, the query language should allow knowledge extraction rather than "pinpointing" knowledge in the base. Answers are "copies" of base subgraphs. Thus, answers result from the construction of isomorphic graphs of images of proofs.

Since answer graphs are constructed up to an isomorphism, two isomorphic graphs should be considered equal. The set of answers is no longer a set of subgraphs of B, but rather a set of graphs isomorphic to images of proofs subgraphs of B. In such a set of answer graphs there are no two isomorphic graphs. Definition 4 (Graph set (iso-set)). A graph (iso-)set {G 1 , ..., G n } is a set of graphs in which, for all i, j with i = j, G i is not isomorphic to G j .

Hereafter, the term "set of graphs" is short for the preceding iso-set notion (a set has no more two isomorphic graphs) 2 .

An iso-answer is an answer notion corresponding to computation of all isomorphic graphs to images of proofs. On the example, R ISO (Q, B) is equal to graphs in figure 4.

Definition 5 (Iso-answer).

An iso-answer from Q to B is an isomorphic graph corresponding to an image of a proof from Q to B. The set of iso-answers is

R ISO (Q, B) = {G | where G i ∈ R IP (Q, B) with G i isomorphic to G}
With this answer notion, the link with the base is lost (particularly when the answer has no individual marker) since it is unknown which nodes of the base corresponds to a generic node of an answer, or even how many images of proofs correspond to the same answer graph 3 . Only the proof of the existence of a particular knowledge in the base is preserved with this notion. Thus, one can question the relevance of only considering isomorphism (i.e. a syntactic equivalence) as an equivalence criterion. In our example, graphs R b and R c in figure 4 both state that "there is a cube on top of a cube".

It seems advisable to detect equivalent answers (in terms of semantics) and to only keep one graph of each equivalent class. We define a criterion of such a set of answers :

Definition 6 (Without equivalence criterion). A set of answers R(Q, B) ⊆ R ISO (Q, B) is "without equivalence" iff ∀G i ∈ R(Q, B), ∄G j ∈ R(Q, B) with G j = G i with G i ≡ G j .
Two types of equivalences arise. The first is from the implicit relation of equality of two nodes having the same individual marker. This type of equivalence is avoided by the base normalization; therefore all images of proofs are in normal form (even if the query is not normalized). The second comes from the intrinsic redundancies of the language, and cannot be handled previously, because even if the base and query are irredundant, proof subgraphs are not necessarily irredundant (in the example, image of a proof R 5 is redundant despite that base and query are irredundant).

In each equivalence class, there is a single graph (up to isomorphism) that is the smallest graph of his class: it is the irredundant form. It seems natural to choose this graph to represent one equivalence class of images of proofs. In the example, R IRR (Q, B) is equal to graphs R a and R c in figure 4.

Definition 7 (Irredundant answers). The set of irredundant forms of images of proofs from

Q to B is R IRR (Q, B) = {Irr(G) | G ∈ R ISO (Q, B)}.
This notion of irredundant answers may seem strange because one may think that an answer could not be isomorphic to an image of a proof. The following property holds that the irredundant form of each image of a proof is itself an answer (up to isomorphism) and that the set R IRR (Q, B) does not have equivalent answers.

Proposition 1. R IRR (Q, B) ⊆ R ISO (Q, B) is "without equivalence". Proof. For all G ∈ R IRR (Q, B), there is G ′ ∈ R IP (Q, B) such that G is isomor- phic to Irr(G ′ ). So there is a projection π ′ from Q to B such that π ′ (Q) = G ′ .
There is also, by definition of the irredundant form, a projection π r from G ′ to B such that π r (G ′ ) = Irr(G ′ ). Thus there is a projection π = π r • π ′ from Q to B such that π(Q) = Irr(G ′ ) and so isomorphic copy of Irr(G ′ ) is an answer of R ISO (Q, B). The unicity property of the irredundant form (up to isomorphism) in each equivalence class and our notion of graphs defined up to an isomorphism lead to the conclusion that R IRR (Q, B) is without equivalence.

The notion of answers without equivalence is not sufficient because, as one does not want to keep two equivalent answers, only answers that add new knowledge compared to other answers should be conserved. In the example, answer R a states that "there is a cube that touches cube A and that is on top of a cube" and answer R b states that "there is a cube on top of a cube", so knowledge of R b is expressed by R a . So we introduce a new incomparability criterion in the next section.

Sets of incomparable answers

Two answers are comparable if knowledge stated by the first is deducible4 from the other. Once there are comparable answers in a set of answers, there is redundancy between them. The idea is to eliminate this redundancy by keeping only incomparable answers.

Definition 8 (Incomparability criterion).

A set of answers R(Q, B) ⊆ R ISO (Q, B) is "without redundancy" when all of its answers are incomparable:

∀G i , G j ∈ R(Q, B) with G j = G i , G i G j .
Given a set of answers R ISO (Q, B) there is not a single subset "without redundancy" (e.g. {R a } or {R b }). A natural constraint is to make such a subset to not remove too many answers, i.e it has to be maximal by inclusion.

Definition 9 (Maximality criterion).

A set of incomparable answers R(Q, B) ⊆ R ISO (Q, B) is "maximal" when no other answer can be added without adding redundancy:

∀G ∈ R ISO (Q, B) \ R(Q, B), ∃G ′ ∈ R(Q, B) such that G ′ ≤ G or G ≤ G ′ .
This notion still does not ensure unicity of such a subset. One can want to constrain a bit more the notion of maximality by forcing the subset of answers R to be complete, as one wishes that all of the answers of R ISO (Q, B) can be deduced from answers of the subset. We thus extend the logical interpretation operator Φ from SGs to sets of SGs by taking the conjunction of logical formula associated with each graph of the set : so if R = {r 1 , ...r n }, Φ(R) = Φ(r 1 ) ∧ ... ∧ Φ(r n ).

Definition 10 (Completeness criterion). A set of answers

R(Q, B) ⊆ R ISO (Q, B) is complete iff Φ(S), Φ(R(Q, B)) |= Φ(R ISO (Q, B)).
We call the normalized disjoint union (N ormalizedDisjointU nion) of a set of graphs E, the normal form of the graph resulting from the join of nodes and edges (and labeling functions) of graphs of E.

Proposition 2. A set of answers R(Q, B) ⊆ R ISO (Q, B) is complete iff the normalized disjoint union of R(Q, B) is more specialized than all of the answers of R ISO (Q, B), i.e. ∀G ∈ R ISO (Q, B), N ormalizedDisjointU nion(R(Q, B)) ≤ G.
The proof is trivial, note that Φ(N ormalizedDisjointU nion(R(Q, B)) ≡ Φ(R(Q, B)). Corollary 1. A set of complete incomparable answers is maximal.

The completeness criterion still does not ensure unicity of a subset of answers (because of equivalent answers). A natural choice is to take the smallest set of answers. This leads to the definition of a minimality criterion based on a notion of answer size and equivalence of answers sets. Definition 13 (Minimality criterion). A set of answers R(Q, B) ⊆ R ISO (Q, B) is minimal iff there is not an equivalent set of answers with a strictly smaller size.

Proposition 3. R(Q, B) is minimal iff R(Q, B) ⊆ R IRR (Q, B).
Corollary 2. Each minimal set is unique (up to isomorphism).

The previous proposal and its corollary can be easily deduced from irredundant graph properties.

Completeness and minimality constraints define a notion of answer that seems more appropriate when one searches to retrieve knowledge stored in a knowledge base. Definition 14 (Most specific answers). The set of the most specific irredundant answers is

R M IN (Q, B) = {G ∈ R IRR (Q, B) | ∄G ′ = G ∈ R IRR (Q, B) with G ′ ≤ G}. On the example, R M IN (Q, B) is equal to graph R a in figure 4.
(Q, B) is complete because each answer of R ISO (Q, B) is equivalent to a graph of R IRR (Q, B). By the definition of R M IN (Q, B), one deletes in R IRR (Q, B) only G i which is more general than another graph of R IRR (Q, B). Thus, R M IN (Q, B) is complete. • Minimality and unicity: R M IN (Q, B) is a subset of R IRR (Q, B
), thus it is minimal and unique w.r.t. corollary 2.

⊓ ⊔

One can define an answer notion like that on the most specific element, but this time with the most general ones. This notion is like a "summary" of the set of answers: not all of the answers are returned, but a minimal subset generalizing all of the answers.

Definition 15 (Summary

). A set of answers R(Q, B) ⊆ R ISO (Q, B) is a summary iff it is minimal and it generalizes all of the answers of R ISO (Q, B), that is ∀G ∈ R ISO (Q, B), ∃G ′ ∈ R(Q, B) such that G ′ ≥ G.

Definition 16 (Maximal answer). The set of all of the most general irredun

- dant answers is R M AX (Q, B) = {G ∈ R IRR (Q, B) | ∄G ′ = G ∈ R IRR (Q, B) with G ′ ≥ G}. Property 1. R M AX (Q, B)
is the sole minimal and maximal subset of incomparable answers of R ISO (Q, B).

The proof is similar to the proof of property 1. In the example, R M AX (Q, B) is equal to graph R c in figure 4.

Case of bases composed of (only) individual concepts

A special case is when a knowledge base does not contain any variables (corresponding to relational databases). In such bases, there is only a kind of redundancy from redundant relations between concepts (relations whose type is comparable and with the same ordered set of neighbors). Computation of the irredundant form is thus linear and incremental. Proposition 4. In an irredundant base whose concepts are all individual, all of the images of proofs of any query on this base are non-isomorphic and irredundant.

Proof. A base in normal form and which only contains concepts that are individuals does not contain concept nodes with the same label (nor comparable concept nodes in terms of specialization/generalization). Moreover, as the base is irredundant, it does not contain redundant relations between concepts (all the more with the same label). So there is not any isomorphism (or projection) from a subgraph of the base to another (except identity relation). Images of proofs are base subgraphs so they are non-isomorphic. They are irredundant because none of the base subgraph can be projected in one of its strict subgraphs (since there is no projection from a base subgraph in another, except identity).

⊓ ⊔ Corollary 3. If B is irredundant, for any query Q there is a bijection from the set of images of proofs R IP (Q, B) to their copies R ISO (Q, B), and R ISO (Q, B) = R IRR (Q, B).

Conclusion

In this paper we define two main notions of answers to a query in the knowledge base querying framework: the first is composed of base subgraphs that can allow browsing in the knowledge base or that can be used as a first step to update queries; the second consists of graphs independent of the base. We define several good criteria for this last notion: the non-equivalence of answers, the incomparability of answers, the completeness of a set of answers, and the minimality (in terms of size) of a set of answers. The most interesting notion of answer w.r.t. these criteria is the set of the most specific irredundant answers. However, in one of our projects, we need the notion of answers of the set of most general irredundant answers, as these answers are used as the body of new queries in another knowledge base. An another answer notion, not developed in this paper is the construction of a graph resulting from the disjoint sum of all answers. the definition of such a notion gives a closed querying system (query, knowledge base and answer are in the same formalism) and allows us to reuse the result of a query as a knowledge base (nested queries).

Finally, in this paper, we overcome redundancies between answers by deleting answers. Another possibility is to overcome redundancies (when it is not a redundancy of the knowledge base itself) by completing answers by the addition of knowledge from the base allowing to differentiate redundant answers. We are currently working on a definition of such an answer contextualization mechanism. This kind of mechanism seems relevant for such knowledge bases because, contrary to relational databases in which a hypothesis is put forward that the creator of the request knows the schema of the database, they are by definition weekly structured and the only reasonable hypothesis put forward is that the creator can verify that his query is correct w.r.t. the ontology. A contextualization mechanism thus allows to respond to queries of the type: "What knowledge can I have on animals owned by Mary?" with a set of such answers : { "Mary owns a pedigree animal", "Mary owns a cat offered by her father","The preferred animal that Mary owns is a cat"} rather than the only answer "Mary owns a cat".

Fig. 1 .

 1 Fig. 1. Three equivalent SGs built on a support.

Fig. 2 .

 2 Fig. 2. Base and query (with named vertices).

Fig. 3 .

 3 Fig. 3. The five subgraphs composing RIP (Q, B) .

Fig. 4 .

 4 Fig. 4. Graphs composing RISO(Q, B) .

Definition 11 (

 11 Answer size). The size of a set of answers R(Q, B) is the sum of the number of nodes of all answers: Σ g∈R(Q,B) card(g). Definition 12 (Answers sets equivalence). Two sets of answers R(Q, B) and R ′ (Q, B) of a query Q on base B and consistent w.r.t. a support S are equivalent iff Φ(S) |= Φ(R(Q, B)) ↔ Φ(R ′ (Q, B)).

Theorem 1 .

 1 R M IN (Q, B) is the only complete minimal and incomparable subset of answers of R ISO (Q, B). Proof. • Incomparability: R M IN (Q, B) is by definition composed of the most specific elements of R IRR (Q, B), and as two elements of R IRR (Q, B) are not equivalent, all of the answers of R M IN (Q, B) are incomparable. • Completeness: R IRR

Note that our irredundant definition is stricter than that given in[START_REF] Chein | Conceptual Graphs: Fundamental Notions[END_REF].

The images of proofs sets can contain isomorphic subgraphs (if they are not the same subgraph of the base).

The open world assumption of knowledge bases does not indicate whether two different but isomorphic images of proofs represent the same "situation" of the world, or two similar "situations".

One could distinguish cases of a simple knowledge inclusion from cases of general deduction by using ontology knowledge, depending on the level of ontology knowledge appropriation by the user.

⋆ This work is supported by the Eiffel project, funded by ANR-RNTL.


Flora Carrasco
email: carrasco@laplace.univ-tlse.fr

Laurent Berquez
email: berquez@laplace.univ-tlse.fr

Kunihiko Tajiri
email: tajiri.kunihiko@ab.mitsubishielectric.co.jp

Didier Hirotaka Muto
email: muto.hirotaka@da.mitsubishielectric.co.jp

Marie-Laure Locatelli
email: locatelli@laplace.univ-tlse.fr

Sombel Diaham
email: diaham@laplace.univ-tlse.fr

Virginie Griseri
email: griseri@laplace.univ-tlse.fr

Thierry Lebey
email: lebey@laplace.univ-tlse.fr

Gilbert Teyssedre
email: teyssedre@laplace.univ-tlse.fr

Carrasco Flora

Laplace

Didier Marty-Dessus

Effect of film thickness and electrode material on space charge formation and conductivity in polyimide films

Keywords: polyimide, passivation, DC stress, space charge, electrode material, LIMM

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I. INTRODUCTION

In recent years, high temperature electronics and power electronics applications have emerged needing the use of wide bandgap semiconductor (SiC, GaN…). In these devices, substrates coated with thin polymer films have been widely used. Particularly, polyimide is of great interest owing to its excellent thermal and electrical properties and its easy processing. Some of the most important applications of these materials films are as inter-level dielectric insulators and as electronic device surface passivation [START_REF] Zelmat | Investigations on high temperature polyimide potentialities for silicon carbide power device passivation[END_REF].

Space charge is generally reported as a triggering mechanism for the degradation of insulations [START_REF] Mazzanti | Electrical aging and life models: the role of space charge[END_REF]. However, space charge mechanisms have been rarely studied and still remain unclear in thin PI films, presumably for a lack of suited method for film thickness in the µm range. Previous works have reported on a significant impact of the electrode material [START_REF] Kaneko | Effects of electrode material on injection and space charge formation in polyimide[END_REF][START_REF] Sessler | Electrical conduction in polyimide films[END_REF] and PI-thickness [START_REF] Liang | Effect of film thickness on the electrical properties of polyimide thin films[END_REF] on the electrical behavior of PI. Kaneko et al. showed the absence of clear influence of the electrode material on the space charge dynamics [START_REF] Kaneko | Effects of electrode material on injection and space charge formation in polyimide[END_REF] whereas Sessler et al. pointed out that steady state currents could be determined by the electrode-polymer interface [START_REF] Sessler | Electrical conduction in polyimide films[END_REF]. Liang et al. investigated the influence of the PI-films thickness on the dielectric constant and on conduction current in PI samples with thicknesses of 80-2000 nm [START_REF] Liang | Effect of film thickness on the electrical properties of polyimide thin films[END_REF].

In the present paper, an experimental study of the space charge dynamics in polyimide films is presented. This is achieved by Laser Intensity Modulation Method with applying a cumulative DC stress on samples for a positive and a negative polarity. These experiments were supplemented by conduction currents measurements. The impact of the electrode material and of the PI-layer thickness on the space charge and on the conductivity have been studied using Au or Al top electrode metals and 12 or 18 µm thick PI-layers, respectively.

II. EXPERIMENTAL DETAILS

A. Samples

The tested samples are Metal-Insulation-Semiconductor (MIS) structures as depicted in Fig. 1. Polished <100> Sisubstrates, of a few hundred micrometers in thickness and 3" in diameter, highly doped with phosphorus (n-type, resistivity between 0.001 and 0.003 Ω.cm) have been used as bottom electrode. The PI-layer was deposited by spin-coating onto the wafer. Top electrodes of 150 nm in thickness and 16 mm in diameter were sputtered under vacuum onto the upper surface of PI. Moreover, a layer of nickel was deposited on the bottom face of the substrate to avoid oxide formation.

In order to assess the impact of the electrode material and of the PI-thickness, three stacks of samples were preparedthe first one with Au/PI-18 µm, the second one with Au/PI-12 µm and the last one with Al/PI-18 µm. The PI-thickness was determined by using a mechanical profilometer.

Moisture has an important influence on the electrical properties of PI [START_REF] Xu | Dielectric relaxation and deuteron NMR of water in polyimide films[END_REF]. Therefore, all the samples were dried during 7 days at 150°C in an air-oven before any experiments to avoid any influence of water ingress on the PI dielectric response. Moreover, all the samples were electrically virgin before their characterization.

B. Space Charge Measurements

The LIMM is a thermal based method dedicated to the characterization of space charge dynamics in thin dielectric films (thicknesses typically ranging from 5 μm to 50 μm) [START_REF] Lang | Laser-intensity-modulation method: A technique for determination of spatial distributions of polarization and space charge in polymer electrets[END_REF].

In the LIMM, the tested sample -placed in a measuring cell and with both surfaces coated with opaque electrodesis exposed to a laser beam (654 nm) which is intensitymodulated with a square wave signal (see Fig. 2). The absorption of the beam by the top electrode of the sample produces local heating. The modulation of the laser diode beam causes a periodic fluctuation in temperature of the top electrode and results in the propagation of non-uniform thermal waves across the sample. Varying the modulation frequency of the laser beam leads to a modification of the size of the thermal diffusion zone and allows probing more or less deeply the structure under study. This heat flux interacts within the dielectric layer, leading to a rebalancing current between the electrodes. The AC current is preamplified and extracted from the noise by the way of a lockin amplifier. A mathematical deconvolution technique is then used to compute the polarization and. space-charge distributions from the current-frequency data [START_REF] Petre | A comparison of different mathematical treatments for solving the inverse problem in focused laser intensity modulation method[END_REF].

The polarization steps consist in applying a DC electric field (from 25 up to 125 kV/mm, by steps of 25 kV/mm), with positive or negative polarity, on the top electrode of the sample during 1 hour in air and at room temperature. The Sisubstrate was grounded. After each polarization step, a depolarization, consisting in short-circuiting the sample during 1 hour, was performed. A cumulative protocol was applied for successive voltage steps. LIMM measurements were completed throughout the whole protocol. LIMM currents were measured for 63 frequencies, between 10 1 and 10 4 Hz. LIMM results discussed here were obtained in voltoff short-circuit after each polarization step.

C. Conduction Current Measurements

To complete the space charge study, some conduction current measurements were carried out in air and at room temperature. The DC high voltage was applied on the top electrode through needles connected to micro-positioners while the Si-substrate was grounded. The transient current was measured using an electrometer with an accuracy of 10 -14 A. The voltage rising sequence was the same than for the space charge study one -the only difference is the application time. Once one voltage was applied, transient currents were measured during 30 min with a time step of one second. Before increasing the voltage magnitude, the sample was short-circuited during 30 min.

The DC conductivity of the sample was estimated from the transient charging current measured during the last minute at each voltage step.

III. EXPERIMENTAL RESULTS AND DISCUSSION

A. Effect of DC stress level and polarity on the electrical behavior of PI Fig. 3 and Fig. 4 represent respectively the internal electric field and space charge distribution obtained on Au/PI-18 µm samples by the LIMM after deconvolution. Profiles analyzed herein were obtained 10 min after the polarization switch off. Results are shown for both polarities. It is important to note that the space charge magnitude contains some errors close to top electrode surface compared to the deeper side.

When a positive voltage is applied on the top electrode (see Fig. 3a,4a), negative charges are detected in the bulk of the PI-layer. A build-up of these negative charges occurs as the applied field is increasing. Correspondingly, the internal electric field exhibits increasing values as the external voltage is rising. The residual internal field is negative in the vicinity of the gold electrode and positive in the rest of the sample (providing therefore field intensification under polarization). In addition, it can be noted that the charge is almost zero in the vicinity of the substrate.

When the polarity is reversed (see Fig. 3b,4b), a build-up of negative charges is still observed in the bulk of the samples, but some positive charges are detected in the vicinity of the wafer, albeit with a smaller amount than negative charges. Compared to the positive polarity, negative charge amount is clearly higher for the negative polarity. Furthermore, the residual internal field becomes positive in the vicinity of the Si-wafer. Fig. 5 represents the DC conductivity plotted versus the applied electric field for both polarities as obtained on samples with the structure Au/PI-18 µm. The error bars have been calculated from the dispersion of current data.

For Au/PI-18 µm samples, under both polarities, the DC conductivity exhibits increasing values with the external electric field.

B. Influence of the PI-layer thickness on the electrical

behavior of PI Fig. 6 represents the internal electric field distributions for Au/PI samples with a thickness of 12 and 18 µm after 1h of polarization at ±125 kV/mm. The impact of the PI thickness is seen mainly on the field profiles, hence the choice of representation done in Fig. 6. The internal electric field profile is similar for both thicknesses whichever the polarity. The main difference is at the level of the positive maximum value: the thicker the PI-film, the higher the internal field intensity for both polarities.

The DC conductivity versus the electric field for 12 µmthick and 18 µm-thick samples is plotted in Fig. 7. The conductivity is increased when the PI-layer is thinner. Liang et al. reported also this trend on the conduction current [START_REF] Liang | Effect of film thickness on the electrical properties of polyimide thin films[END_REF]. C. Influence of the electrode material on the electrical behavior of PI Fig. 8 compares the charge density distributions for samples with a top metallization of Au and Al after 1h of polarization at ±125 kV/mm. Contrary to the thickness, the electrode material has an important impact on the charge density. The shape and magnitude of charge density are similar for both electrodes under a positive polarity. However, for a negative polarity, even if in both cases there are negative charges in the bulk of the PI-layer and positive charges in the vicinity of the Si-substrate, the shapes of profiles are different. The amount of negative charges is clearly smaller when the sample is metallized with Al.

A comparison of the DC conductivity of 18 µm-thick samples provided with Au and Al metallizations is done in Fig. 9. Surprisingly, the conductivity is similar under a negative polarity but different with a positive polarity, whereas for the space charge study, the impact of the aluminium electrode is observed only under a negative polarity. In contrast, under a positive polarity, the conductivity of the sample metallized with aluminium is clearly higher than the conductivity of samples with a gold electrode.

D. Discussion

In the previous section, the influences of the applied field strength, voltage polarity, electrode nature and PI-thickness have been assessed on the space charge and on the conductivity of PI. The LIMM appears as a suited method to investigate space charge distribution in PI films as thin as 10 -20 µm in MIS structures.

Whatever the sample structure, the increase in the applied voltage implies a build-up of negative charges in the sample bulk and, as a consequence, an increase of the residual internal field, which is positive. Moreover, whatever the sample structure, the application of a negative polarity on the top electrode generates the presence of positive charges in the vicinity of the silicon substrate and an internal electric field which becomes negative after a normalized depth of around 0.4 here.

Space charge build-up may be due to electronic carrier injection from the electrodes followed by displacement in the bulk. For a positive polarity, the negative charges can result from the injection of electrons from the n-type substrate followed by their drift towards the top electrode. For a negative polarity, electrons must be injected from the gold electrode. The observed positive charges may come from the Si-substrate, explaining the smaller amount.

In order to compare the impact of the electrode material and PI thickness, the maximum of negative charge density and maximum of internal electric field -positive -are plotted as a function of the applied electric field and polarity in Fig. 10.

Regarding the PI thickness, the charge profile is similar for both thicknesses. However, the internal electric field is decreased for the lowest thickness under both polarities. In parallel, the conductivity is increased, whatever the polarity and the applied field.

Results from section III.A indicated that under negative polarity, an injection of electrons from the top electrode takes place. The study with the Al electrode is along this direction as it reveals a sensitivity of the amount of stored charge to the nature of electrode. The fact that the stored negative charge amount decreases with the Al electrode could be linked to a change in the barrier to injection. The fact that Al oxidizes rather easily could strengthen the barrier to injection. Indeed, it is known that oxide can act as a barrier against electrons injection [START_REF] Koehler | Tunneling through a metal/polymer interface containing a thin oxide layer: Discussion of the consequences of oxide presence on charge injection[END_REF].

At this level of work, establishing a direct link between space charge dynamics and conduction phenomena is still ongoing.

IV. CONCLUSION

Space charge distribution profiles in PI thin films have been probed by LIMM under DC electric fields in the range ±25 to ±125 kV/mm. Space charge measurements show strong dependence of the response of the PI as a function of the polarity and of the DC stress. A large increase in negative charges depending on a DC stress was observed under both polarities, which suggests that electron injection from the silicon substrate occurs in PI under a positive polarity and that negative charges can also be injected from the top electrode under a negative polarity. Two thicknesses (12 and 18 µm) of PI-layer and two electrode materials (gold and aluminum) were used and compared. The PI thickness has a substantial impact on the internal electric field enhancement and the conductivity. The native alumina layer formed between the Al top electrode and the polyimide acts very likely as an electronic barrier. Further investigation is necessary to understand the link between conduction phenomena and space charge dynamics.

Fig. 1 .

 1 Fig. 1. Cross-sectionned sketch of the MIS samples structure.

  Fig. 3. Internal electric field distribution at different DC voltages for both polarities -Au/PI-18 µm structure. Fig. 2. Sketch of the LIMM experimental set-up.

Fig. 5 .

 5 Fig. 5. DC conductivity vs. applied electric field for both polarities -Au/PI-18 µm.

Fig. 4 .Fig. 6 .

 46 Fig. 4. Charge density profile at different DC voltages for both polarities -Au/PI-18 µm structure.

Fig. 8 .Fig. 7 .Fig. 9 .

 879 Fig. 8. Charge density under a positive (a) and a negative (b) polarity vs. normalized depth (with the thickness of the sample) after 1h of polarization at ±125 kV/mm -Comparison of electrode materials; PI-18 µm.

3 )

 3 Fig. 10. Maximum of internal electric field (a) and of charge density (b) vs.applied electric field for both polarities -Comparison of the three sample structures.

ACKNOWLEDGMENT

The authors wish to thank B. Schlegel for his kind help in sample preparation.