Transformative movements in two shrinking West African mining towns

 and 2017 (Anonymized, 2018).

Research consisted of altogether seven months of participant observation and interviews over a period of five years, partly based on… [Anonymized] (Anonymized, 2018). In 2017, we conducted another 60 semi-structured interviews with stakeholders (miners, managers and other city dwellers; local administrators, politicians, and activists; farmers around the mines) in Fria and Obuasi and did small quantitative studies on changes of municipal budgets, household incomes, and enrollment rates due to mine closure.

Until today, most of the literature on mine closure is business-related and is aimed at 'proper' (World Bank and International Finance Corporation, 2002: v) or 'sustainable' (Lawrence, 2006: 298) mine closure (see next section). If the industry would consider the insights of these studies when constructing new mines, many pitfalls of mine closure could be avoided.

However, even if all of the proposed measures would be implemented, African mining remained far from 'sustainable', as long as the concerned local and national population does not effectively take control of the exploitation and the processing of its own resources.

Unfortunately, control relations have worsened over the last 40 years. In an article on the right to the city, which will strongly influenced this article, Harvey (2008: 31) states that in the past three decades of restoring class power to rich elites, cities increasingly developed into 'fortified fragments, gated communities and privatized public spaces kept under constant surveillance'. These changes happened much faster and much more radical in the developing world, where cities seem to become 'microstates' (cf. the notion of the enclave; Ferguson, 2005), separated into wealthy neighbourhoods and shanty towns, 'where water is available only at public fountains, no sanitation system exists, electricity is pirated by a privileged few, [and] the roads become mud streams whenever it rains' (Balbo, 1993; cf. Harvey, 2008: 31). This description of the 1990s comes quite close to the situation we encountered in the mining town of Fria in Guinea, one our two case studies. Prior analyses showed that the mining town

INTRODUCTION

Mine closure has become an increasingly important issue since the end of the mining boom in the aftermath of the sub-prime crisis. All over the world, companies felt forced to either reduce production and personnel, or to close mines completely. Overinvestment in the mining sector in the years before the crisis prevented most extractive industries from profiting from higher global growth rates in recent years. This economic pressure is enforced by the fact that at least 25 major mines in the global South were already scheduled for closure before the mining boom started in the early 2000s (World Bank and International Finance Corporation, 2002: 16;cf. Mining Minerals and Sustainable Development, 2002). Whereas the mining boom of the 2000s extended the lifespan of many of these mines, the economic crisis that followed shortly thereafter brought to an end these 'Methuselahs', as well as a number of mines that seemed perfectly profitable before the cooling of the world economy. Particularly in extraverted, resource-rich countries with weak governmental institutions, this led to multiple crises due to the stop of provisions with potable water and electricity, the collapse of local and regional health systems, sustained environmental contamination, high unemployment rates and the sharp decline of (local) governmental income (cf. Anonymized, 2018: 70-120;Lawrence, 2006: 286).

We approach this topic from the point of view of discussions about the 'right to the city' (Harvey, 2008;Lefebvre, 1996;[START_REF] Souza | Which Right to which City? In defence of political-strategic clarity[END_REF]. This literature overlaps in its analysis of social struggles and their politico-economic background with debates on 'shrinking cities' (Martinez-Fernandez et al., 2012b;Martinez-Fernandez et al., 2012a). Most authors argue for effective participation in decision-making and bottom-up control over the means of distribution (and production) in the concerned cities (see e.g. Mitchell, D. 2003;Hollander and Németh 2011: 358). In this paper, we will focus on transformative movements and projects as one particular aspect of this literature.

Building on these discussions might be considered inappropriate because they have hitherto primarily focused on social movements in large cities of the old industrial centres like Paris, is much more part of a transnational 'company polity' than of the formal political hierarchy on the national scale (Anonymized, 2018: 45). This means that its already fragile democratic institutions are increasingly sidelined by the 'direct power' (Harvey, 2008: 38) of a de facto despotic transnational company hierarchy (Anonymized, 2018: 45), which is increasingly masked by consultation frameworks, stakeholder workshops, round tables, and the like.

Currently, Guinean bauxite mines provide full-time employment for less than 10,000 workers, who are in turn responsible for more than half of the country's foreign currency. At the same time, the population hardly profits from tax payments and strongly suffers from the politicoeconomic and environmental consequences of extractivism (see Anonymized, 2018: 70-120).

In Ghana, as in many other African countries, political institutions are stronger, but industrial gold mining is in the hands of several foreign investors and provides jobs for several thousand miners, while hundreds of thousands of Ghanaians could make a living from small-scale mining in Obuasi alone.

In both case studies, we focused on the possible transformative impulses of the decline of such company towns. We identified movements for an abandonment of extraverted extractivism at the fringes of the 'company polity' and around the cities, and to a certain extent among workers' children who strive for an urban future without industrial mining.

EXISTING LITERATURE

Mining in Sub-Saharan Africa shares many aspects with mining in the old industrialized centres: Mining towns are (1) mostly located in areas that are economically and physically peripheral; (2) are left out of global knowledge flows; (3) face environmental degradation and negative health impacts, and (4) experience high unemployment rates due to various reasons, including, for instance, the exhaustion of reserves, increased productivity because of advances in mining technology, and the long-term effects of the post-Fordist reorganization of the industry (subcontracting; increasing use of fly-in, fly-out operations, and continuing cost savings in non-core business activities; Magrin, 2013: 203;Martinez-Fernandez et al., 2012b: 247-8). However, contrary to most mines in the old industrialized centres, mining in Sub-Saharan Africa additionally goes along with capitalist over-exploitation, operating on the basis of 'accumulation by dispossession' (Harvey, 2008: 34), which leads to extraverted economies and 'spatial schizophrenia' (Magrin, 2013: 201-10), or, in other words, a profound disarticulation of economic and political space (see e.g. Becker et al., 2007: 18;Magrin, 2013: 360). Economic components of these global control relations have received considerable attention in debates about the so-called 'resource curse' (Magrin, 2013: 103-37;Sachs and Warner, 1995), recently also on the local scale (Littlewood, 2014: 3;Martinez-Fernandez et al., 2012a: 247). In practical terms, this means that, most of the time, mining in the global South goes along with political instability, forced displacement, disrupted and destroyed livelihoods, and violent conflicts on different scales (cf. Brand and Wissen, 2017;Campbell, 2009;Fischer et al., 2016). This also affects decision making and planning in such mining towns. When mines close, the gap between corporate and governmental discourse about 'sustainable mining' and realities on the ground usually increases, because, by that time, the local population has both learnt how to make demands and experienced a variety of negative consequences of mining, whereas the willingness of mining companies to invest in their 'social licence to operate' is comparatively low [START_REF] Van Vliet | Activités minières, barrages, et problématiques de négotiation: hypothèses pour une réflexion[END_REF]cf. Magrin, 2013: 205). In addition, closure planning in low income countries is complicated by the fact that few regional employment possibilities and internal displacement, due to mining activities and other causes (see e.g. Kamete, 2012: 599), most of the time lead to 'parallel informal settlements' (Littlewood, 2014: 37) and to post-mining economic activities, such as small-scale mining and scrap-metal collection (Limpitlaw and Digby, 2014: 1). Combined with the local population's much higher dependency on social services and infrastructure maintenance, provided by private companies during exploitation, this renders mine closure much more difficult and conflictual than in high-income countries.

Despite these considerable challenges, many researchers decry the fact that most of the literature on mine closure focuses on environmental and technical aspects, and ignores social and political issues (Harfst and Wirth, 2011: 175;Lawrence, 2006: 286;Lochner and Cloete, 2013: 78;Martinez-Fernandez et al., 2012a: 256;Mining Minerals and Sustainable Development, 2002: 3;Peck and Knud, 2009: 227). When social issues are mentioned, they are mainly treated from either a company point of view (see, e.g., Esteves, 2008;Fourie and Brent, 2006;International Council on Mining and Metals, 2008;Lawrence, 2006;Lochner and Cloete, 2013: 78), or in the technocratic and functionalist manner of development agencies and governmental bodies, which mostly rely on the hope that better (social) techniques lead to more development (see, e.g., Commonwealth of Australia, 2006;Environment and Security Initiative, 2005;Neil et al., 1992;World Bank and International Finance Corporation, 2002) and underline the feasibility and economic viability of 'proper' (World Bank andInternational Finance Corporation, 2002: v), 'acceptable' (Peck andKnud, 2009: 228) or 'sustainable' (Lawrence, 2006: 298) mine closure (for discussion see also Littlewood, 2014: 37;[START_REF] Whitmore | The Emperor's New Clothes: Sustainable Mining?[END_REF].

Within this body of literature, there is nonetheless a broad consensus about the fact that many negative consequences of mine closure could only be avoided by differently planning and constructing mining towns from the beginning (Neil et al., 1992;World Bank and International Finance Corporation, 2002: v). This involves the establishment of closure funds (or insurances, see Peck and Knud, 2009: 227), the stimulation of diversification, as well as infrastructural considerations. For instance, if mining towns are connected to the national grid, the population is less likely to lose its access to electricity after mine closure. The same goes for the economic potential of roads and railways, and for economic diversification in general.

However, these challenges are presented as technical problems that can only be solved by the intervention of experts without considering already existing propositions and practises of the population itself, and without referring to the global politico-economic context.

We propose to close this research gap by drawing on the concept of the 'right to the city', arguing that in spite of their quite different role in the spatial organization of capitalist production, declining company towns in the 'North' and mining towns in the 'South' are confronted with similar problems. Demands for the right to the city have undergone profound changes since the coining of the term in the late 1960s by Henri Lefebvre [START_REF] Souza | Which Right to which City? In defence of political-strategic clarity[END_REF]. To Lefebvre, the right to the city meant the right to anti-capitalist 'autogestion', and it was a starting point for the creation of a whole new society (Souza, 2010: 318). Harvey (2008: 23) similarly talks of the right to 'change ourselves by changing the city'. In current discussions about shrinking cities, this revolutionary verve has mostly transformed into what could be called 'degrowth' movements (see Eversberg and Schmelzer, 2015;cf. Brand, 2015). Several shrinking cities (for example, Detroit, Flint, or Youngstown) have become testing grounds for new forms of living, which do not aim at renewed economic and population growth. City maps are redrawn, and liberated space in the city centres is used for agriculture, desegregation projects, art installations, etc. In the eyes of new city dwellers, who were attracted by these projects, these cities show how differently society can be organized. 2At first sight, this radical, transformational potential is not discernible in the case of declining African mining towns. As industrialization has never set in in most African countries, how should there be a social movement for deindustrialization? Most city dwellers who have moved to these towns yearn for their first car, their own house, and save money to send their children to school abroad (cf. Brand, 2015: 19-21;Gudynas, 2012a). However, as has already been pointed out, the 'reality' of African mining is also one of recurring deceptions: For most inhabitants, the modernist dream does not work out or is short-dated (cf. Ferguson, 1999;Fraser and Larmer, 2010). These deceptions lead to post-extractivist movements 3 , both on the countryside near the mines where the negative effects are the strongest, and in the city centres (led by young, educated elites), which aim at more comprehensive societal change. In the following two sections, we will briefly recount the consequences of mine closure and then analyse the transformational potential of current demands for the right to the city in Fria and Obuasi.

REASONS AND CONSEQUENCES OF MINE CLOSURE

We have chosen these two cities because they share a number of similarities: Both have been constructed with the help of colonial powers -Obuasi by the end of the 19th century, and Fria in the 1950s -and both have corresponded to what could be called the paternalist model of mining, which led to the creation of all-inclusive, corporate enclaves (see Ferguson, 2005), being almost independent of national services (cf. Pauthier, 2002;Rubbers, 2013). Due to their shopping malls, sports grounds, modern hospitals, schools, nightlife, etc., both Fria and Obuasi developed into points of attraction for the national elite (Soumah, 2008: 215). In combination with comparatively high wages in the mines, this also led to fast population growth at the cities' outskirts, based on the provision of all sorts of services for the upper 10,000. 4 Structural differences between Fria and Obuasi concern the different materiality of the mines' output, the location of the cities, and the role of public institutions. Living in one of the most important African gold towns, the inhabitants of Obuasi were always involved in artisanal and small-scale mining (ASM). This led to continuous conflicts with industrial miners, which have intensified with the start of industrial surface mining in the 1990s (Commission on Human Rights & Administrative Justice, 2008: 42). Fria, a bauxite mining town, has experienced less violent conflicts and less environmental degradation. 3 The term has been popularized by the Uruguayan ecologist Eduardo Gudynas as part of a critique of recent leftist extractivist projects (neo-extractivism) in Latin America (see Gudynas, 2012b;Fuentes, 2014). 4 Similar developments can be found all over the world (see e.g. Borges, 2012). However, most of the African mining towns stand out because of little pre-existing infrastructure, weak political institutions and strong export dependency. One of the most famous descriptions of the resulting booms and busts and their political and cultural consequences, particularly in terms of the development of "urban" cultures is Ferguson (1999).

However, in both company towns we were able to confirm the hypothesis of van [START_REF] Van Vliet | Activités minières, barrages, et problématiques de négotiation: hypothèses pour une réflexion[END_REF] and Magrin (2013: 205), that closure usually marks the most conflictual moment of mining town histories. In both cities, the civil society was better prepared for making demands than ever and had more reasons than ever to do so. At the same time, the willingness of the companies to make concessions was at its lowest.

Mine closure had stronger negative effects in Fria, first because public institutions are weaker in Guinea; secondly because Fria is located in a more remote area; and thirdly because smallscale mining in Obuasi helped to attenuate economic decline. In addition, mine closure happened much more abruptly in Fria because of an entrenched labour conflict between its Russian management and Guinean workers, which led to a lockout in 2012. Rusal, which had bought the mine in 2006, recalled its Russian personnel, locked the factory, and stopped the payment of salaries, but neither licenced the Guinean personnel nor put them on leave and reduced the maintenance of infrastructure and services in Fria to a strict minimum. According to Rusal, the mine closed because the Russian personnel was in danger (Anonymized, 2018: 111). Other sources also point to the impending bankruptcy of the company, mainly because of overinvestment shortly before a drastic collapse in worldwide demand for aluminum, and quarrels with several Guinean governments over a processing plant (Anonymized, 2018: 90-117). 5The closure of the mine in Obuasi was equally caused by decreasing profitability and triggered by conflicts with artisanal gold miners, which led among other things to the death of a manager (The Ghanaian Times, 2016; see below). The owner of the facilities in Obuasi, the South African company AngloGold Ashanti (AGA) has mostly recorded losses in Obuasi since its takeover in 2004. The company had nonetheless more time to prepare for mine closure (which happened in 2014), and workers received substantial redundancy payments that slowed down capital flight. In fact, several interviewees confirmed that even new banks were able to open due to these important inflows. Many workers invested this money in (taxi) cars, houses, and shops. However, compared to the high wages in the mines, this new additional income did not take the concerned families very far (Field research 2017).

The strong rise of artisanal mining (to more than 10,000 miners in recent years) did not only lead to conflict, but also provided another cushioning effect during mine closure. 'Illegal' small-scale mining, or 'galamsey' as it is called in Ghana, has been stigmatized in the country for a long time. By the end of 2016, reacting to a strong rise in numbers, the government and industrial mining companies repressed galamsey with increasing violence, for instance by establishing the so-called 'anti-galamsey task force', while at the same time starting a largescale media campaign against them. In spite of the resulting nationwide public consensus against artisanal mining, many interviewed sellers and shop owners underlined the positive effect on business of the rising number of galamsey, and the combined negative effect of stopping industrial and artisanal mining almost at the same time (Field research 2017).

As we mentioned earlier, the institutional capacities and the monetary resources of (local) government officials in Guinea are much lower than those of Ghanaian officials. While in Guinean bauxite mining towns, public funding of infrastructure and social services only amounts to several per cent of the expenditures of mining companies in the 'public good' (mainly through corporate social responsibility measures; see Anonymized, 2018: 169-73); the budget of the Obuasi Municipal Assembly has even been slightly higher than local CSR budgets in recent years. This corresponds to the share of mining taxes in municipal budgets.

While the budget of Fria collapsed after mine closure, public services in Obuasi depended much less on AGA, and the administration even managed to replace decreasing taxes from mining with other taxes (see figure 1; for the case of Fria, no data was available).

[Figure 1. Actual annual receipts of Obuasi Municipal Assembly from 2010-16 in US$ (converted from GHS based on annual exchange rates)] Despite these differences, the following economic downturn was quite similar. In both cities, small surveys at the markets showed that more than 90 per cent of small and medium-sized enterprises (SMEs) saw their turnover drop by more than half in the two years following mine closure. About a third of the respondents even indicated that their revenues fell to less than 20 per cent of the pre-crisis level in the same time span. This economic crisis was accompanied by continuing environmental degradation; violent conflicts between companies, farmers, and small-scale miners; brain drain; and riots due to degrading infrastructure and services. The latter point concerned, for instance, the stop of the maintenance of workers' apartments, power cuts and water shortages. In Fria, the economic downturn also led to a strong degradation of health services and to a food crisis (Anonymized, 2018: 119).

In general, interviewees in both cities complained that 'everything is going down'6 and that the city 'has become like a cemetery'7 or would soon become a 'ghost town'8 , if the company did not come back. In previously more-privileged circles, eating out, shopping on weekends, and the use of a private car have been stopped by many families. More modest families struggled with water and electricity bills, school fees, and rent. In particular, poorer interviewees also bemoaned the halt of additional services and supplements at the same time that the workforce was reduced. This concerned, for instance, buses for workers that were also used for pupils, free medical treatment, free housing for families of workers and public servants, or free food supplies for workers that often made their way into the local markets.

Changes in enrolment rates point to the uneven effects of decline in both cities. While public primary enrolment declined by 15 to 30 per cent in both cities, private secondary education clearly increased in Fria (see figure 2). In Obuasi, we were only able to gather data for one private school, the former company school of AGA. This school lost most of its workers' children in the first year after closure because high school fees were introduced. In the second year, however, due to a strong influx of non-workers' children, enrolment almost attained precrisis levels again. This suggests that a substantive part of former workers (mostly managers) and other local elites did have enough savings to let their children attend classes in prestigious private schools, while public schooling faced declining resources and emigrating teachers.

[Figure 2. Changes in enrolment in Fria and Obuasi, two years after mine closure] The strong decline of public primary schooling in Obuasi also points to higher emigration rates. Obuasi is situated about 60 km (or two hours' drive) from the regional capital, Kumasi, which has a population of 2 million. The comparatively isolated location of Fria makes emigration a more difficult endeavour.

CHANGING POWER RELATIONS

Definitions of the 'right to the city' are quite vague. From the inception of the term in the 1960s until today, it was rather a means of social mobilization than a clearly defined set of rights, or an analytical framework. It led, nonetheless, to countless concrete measures, like, for instance, the establishment of a right to the city in the Brazilian constitution of 2001 (Harvey, 2012: xii). This also holds true for Lefebvre's own definitions, which, in the words of the urbanist Peter Marcuse (2012: 37), were 'more provocative than careful'. Marcuse made out a definition, which is also central to the outcomes of this research. According to Lefebvre (1996: 158), 'the right to the city is like a cry and a demand. This right slowly meanders through the surprising detours of nostalgia and tourism, the return to the heart of the traditional city, and the call of existent or recently developed centralities'.

To Marcuse (2012: 38), this distinction between 'a cry out of necessity … by those deprived of basic material and legal rights' and 'a demand for something more … an aspiration for the future by those discontented with life as they see it around them and perceived as limiting their potentials for growth and creativity' is crucial to the understanding of current movements.

In our case studies, this 'demand for something more' was mostly made by actors who have actually profited from the pre-crises situation and whose desire for change is based on a variety of reasons, ranging from straight political entrepreneurialism (cf. Bierschenk et al., 2000) to aloof romanticism (but rather the former). The 'cries out of necessity' were expressed by various groups of 'subalterns', with more concrete and immediate aims. Both groups are highly heterogeneous; they can be situated in hierarchies and control relations like class relations, the urban-rural gap, (neo-)traditional systems, gender relations, or seniority. In the following, we will analyse how these different forms of social stratification changed after mine closure in Fria and Obuasi.

We categorized the population of the two cities into four politico-economic groups: (1) a politico-economic elite or bourgeoisie comprised of political leaders, bankers, entrepreneurs, and, most of all, company managers, owning much of the land, hotels, private schools, and the like; (2) a 'workers' aristocracy' (for discussion, see below) of direct employees and certain civil servants; (3) a growing number of precarious contract workers and a similarly growing service sector (ranging from taxi drivers to street hawkers), who are mostly excluded from social services and struggle to make a living in town, and (4) the rural population, which neither profits from economic 'trickle-down' nor from social services. This corresponds to the perception of most urbanists that African mining towns are separated in some sort of protected paternalist 'company polity' and peripheral shanty towns (cf. Pauthier, 2002: 27). This paternalist setting is not only about to crumble (see e.g. Balbo, 1993;Fraser and Larmer, 2010;Anonymized, 2016a: 36), but has always been precarious. For instance, the socially protected realm of Guinean 'company polities' was not only based on spatial and social limits, but has always had, at the same time, temporal limits for workers' families. As social security is virtually non-existent on the national scale, and pensions are very low, workers' families always lost almost all of their privileges when workers retired and had no 'heirs' in the company. This is also why Guinean trade unions fight for higher instead of lower retirement ages (Anonymized, 2018: 103).

Discussions about an allegedly existing 'workers' aristocracy' can be traced back to the 19th century and figure prominently in the oeuvre of almost all influential dependency theorists (for example, Andre Gunder Frank, Giovanni Arrighi, Arghiri Emmanuel, Immanuel Wallerstein, Frantz Fanon, etc.). More recent criticism of the term in the African setting points to the high grade of 'dilution' of this 'elite', and underlines the existence of endurable urban-rural linkages (Ferguson, 1999: 41;Larmer, 2006: 298). In addition, the history of countries like Guinea, Zambia, and Nigeria shows how this image of the African miner as a 'counter-revolutionary' has also been popularized by African 'socialist' despots of the 1970s (Anonymized, 2016b: 142-3;Larmer, 2006: 298;Rubbers and Roy, 2015: 12). 9

In any case, with mine closure, this already fragile and changing social stratification has been strongly shaken: Many workers who had been part of the protected realm before, had no savings. In the best case, this meant accepting work they were often ashamed of; in the worst case, this led to personal crises and total abandonment of the family. For instance, during a taxi drive to an interview with former workers of AGA, we asked our driver several times if he had been a worker before, which he denied. However, when we arrived at the destination, our subsequent interviewees identified this driver as a former worker. Another interlocutor, a sociologist who had grown up as a child of a pool attendant in Fria, talked about psychological 'mass depression' that resulted from the end of the 'dream of modernity' (Anonymized, 2018: 87).

As for most workers, 'modern life' was synonymous with the founding of several families (several wives, also in Christian families) and permanent relations with socially accepted mistresses (cf. Larmer, 2006: 298), mine closure also led to the neglect of many of these women and children (cf. Rubbers, 2010: 335). In Obuasi, this led to the foundation of a 'second wives' association' that primarily aimed at the generation of additional income of these women. This also led to the politicization of many women after mine closure. In Fria, when most workers had already given up their struggle for just compensation, women took 9 Fraser explains this intriguing but nonetheless quite common (cf. Burawoy, 2014: 974) conflict between socialists and unionists, with the new 'job' of governments, after nationalization, in the extractive sector: In a 'state capitalist' system, disciplining the unions was as important to the state as it was to private companies (Fraser and Larmer, 2010: 8;cf. Shafer, 1986: 925). over and organized several successful demonstrations (Anonymized, 2018: 125-7). This certainly led to a decline of paternal authority. However, analysing similar settings in the Democratic Republic of Congo, Benjamin Rubbers (2010: 336) rightly warned about overemphasizing these changing power relations within workers' families. This reshuffling of local power relations also concerned the relation between local business and workers, as the latter became increasingly indebted to the former. In Fria, several shop owners stopped procuring foodstuffs after mine closure because they felt morally obliged to sell them on credit, which would never be repaid. Also in Obuasi, where many workers had received substantial severance payments, workers' consumerist way of life quickly turned many a 'generous gentleman' into a 'beggar'. Similar changes took place in the education sector: For instance, the AGA school is one of the most prestigious schools in Obuasi, and it was exclusively reserved for workers before the crisis. In 2014, AGA outsourced the school without selling it. All staff was sacked only to be hired again under more precarious conditions, and the school introduced high school fees (US$ 300-425 per year). Out of 750 workers' families, about 670 withdrew their children from AGA's school, either because the whole family migrated, or because they couldn't pay the school fees -or both (reliable data on migration is missing). However, due to the fact that many families always wanted to send their children to this school, and, in the words of the new director, due to a new 'product line' (the introduction of a kindergarten), enrolment quickly recovered: After a drop from 1,235 to 848 in year one after mine closure, the number of pupils increased to 1,045 in 2015/2016, this time mostly accommodating children of bankers, administrators, and businessmen.

Another important shift in local power relations concerns small farmers around the mines, who were the only ones who expressed their satisfaction with mine closure, claiming that they had hitherto only suffered from negative consequences of mining. This concerned the destruction of farmland and waterbodies, the end of hunting and the destruction of buildings due to recurrent blastings, and the multiplication of mine-related diseases. Being predominantly analphabets, these peasants were at the same time only very rarely employed by the company, and they were constantly defrauded by company employees and the local administration during compensation procedures for lost farmland (Anonymized, 2016a). In Obuasi, mine closure was triggered when more than 10,000 small-scale gold miners started to occupy mining pits of the company. Many of these galamsey were in fact farmers who had started small-scale gold mining in the 1990s because farming was no longer possible. The partial legalization of these activities after mine closure, based on the handover of 60 per cent of the exploitation permit of AGA to the government, strongly contributed to the amelioration of living conditions in the countryside. Before, many galamsey had lost their lives during police and military raids (Commission on Human Rights & Administrative Justice, 2008). In Fria, land conflicts during exploitation led to less deadly incidents than in Obuasi, and bauxite is not suitable for small-scale mining, but the fact that many of the above-listed negative impacts no longer existed after closure, equally led to an amelioration of living conditions. However, urban-rural relations have not changed enough to talk about a reversal of power relations between cities and the countryside, as it often happens in the case in severe hunger crises, for instance during and after war.

TRANSFORMATIVE IMPULSES FROM MINE CLOSURE

In all of these cases, the changing economic situation led to the questioning of political, social, cultural, and economic institutions. But where did we find the most outspoken advocates for change? The groups that experienced the most pronounced ups and downs in economic and social terms, were probably workers and peasants, with the former being the ones who lost the most (which does not mean that their current situation is the most deplorable) and the latter being the only ones who actually gained from mine closure.

In Fria and Obuasi, workers are at the centre of movements for renewed extractivism, which means either a comeback of the former companies (which is currently happening in Fria), or the takeover of the same mines by another company (which is the most likely future scenario for Obuasi). While workers in Obuasi mainly want their jobs back, the workers' movement in Fria is connected to a conflict over further processing. While taking over in the mid-2000s, Rusal was forced by the government to equally maintain a refinery connected to the mines.

The company would have preferred the processing of bauxite in Russia. One central point of the conflict was that, according to Frian workers, Rusal then deliberately ran down the refinery, by neglecting maintenance and not replacing spare parts (see Anonymized, 2016b: 143-4).

Apart from this extractivist movement, which is by far the strongest movement in the two mining towns because of short-term economic constraints of the population (material needs are far more urgent and basic than in shrinking cities in Europe or in America), we were able to discern two other discourses for change: one that focuses on diversification and entrepreneurialism, and one against the return of mining.

Calls for diversification and the encouragement of local entrepreneurship are very common topics in mining towns. In a way, they are the neoliberal continuation of far more comprehensive, paternalist 'civilization' efforts of the colonial era (cf. Lee, 2014: 62). In colonial mining towns, Africans were to take over the whole package of 'modern' European lifestyle, including religion, gender roles, leisure habits, language, etc. (see e.g. Pezet et al., 2009: 29). Today, citizens of mining towns are said to have lost 'initiative' and the capacity to 'innovate' because 'everything was sucked out by mining'. 10 The new generation of 'civilizing' missions, therefore, focuses on the development of profitability thinking, on the destigmatization of non-mining activities like agriculture and services, and on business skills. AGA, for instance, had created exemplary pig, chicken, and cereal farms, and also planned to create fishponds in abandoned mines. Licenced workers were encouraged to visit a 'job fair' and could take part in a workshop called 'time with the entrepreneur'.11 Around 250 nonworkers were invited to take part in training on the production of beads, pastries, porridge, confectionaries, soap, decoration, and on the reparation of electrical appliances (ibid). In both cities, various groups and individuals (teachers, activists, local politicians, company employees as well as respondents on the street) called for diversification measures, like the creation of education hubs (including universities), health centres (one interlocutor referred, for instance, to Dubai Healthcare City), and tourist attractions (museums and nature). Several of these interlocutors wanted to replace mining with other economic activities; others rather wanted to reduce the dependence of the town on one activity. In most cases, the enthusiastic description of these plans was accompanied by the use of business language. To us, the most striking example of this neoliberal continuation of the paternalist civilizing mission was an interview with the head of the new outsourced school of AGA, who underlined that he had to do a lot of 'marketing' and 'rebranding' to attract new pupils.12 Schoolteachers were now encouraged to improve their 'professional presentation', for instance by wearing ties, shirts, and even pullovers; pupils received new school uniforms instead of the government uniform that had been used before, to create a new 'spirit' because 'students see themselves as being in a school that they can be proud of', and the creation of a kindergarten was announced as a 'new product line' (ibid). In both mining towns, this transformation of the educational sector reflects the change from 'socially thick' to 'socially thin' investment, going along with ever less societal investments, more capital intensive production and increasingly mobile workers (Ferguson, 2006: 36).

Besides this common focus on diversification and entrepreneurialism, mine closure also led to the formulation of more fundamental and movement-based visions of a new town, or a new society. In the case of Fria, the most articulated equivalent to degrowth activists in shrinking cities of the global North is a movement of workers' children, many of whom have ties to Frian diaspora, or who even profited from education abroad and who campaign for a 'future without mines'. One central organization of this movement, the Association des Ressortissants et Sympathisants de Fria (ARSYF) -Association of natives and sympathizers of Fria -organized food aid immediately after mine closure, constructed libraries, acted as a mediator in continuing land conflicts with the company, organized various donation activities, and was about to work out 'Fria Vision 2030', where a post-extractivist strategy should be laid out in detail. Our participation in several ARSYF meetings revealed that this African middle-class movement neither attempted to depict itself in the anti-entrepreneurial way of many European social movements. Based on quite strict organizational procedures, its members are taught how to attract money from foreign donors, how to write letters of application, and how to 'advance in life'. The concept of 'development brokers', developed by Thomas Bierschenk and Jean-Pierre Olivier de Sardan, quite neatly describes these strategies, mindsets, and roles. 13 During a conference about mine closure that we organized together with ARSYF in Fria in September 2017, we were surprised by the amount of infrastructure that the non-governmental organization (NGO) acquired since mine closure with the help of foreign donors. ARSYF possesses, among other things, two computer rooms with about 30 fully functional workstations, where all sorts of training take place. In Obuasi, similar organizations have come into existence after mine closure.

In both case studies, educated activists romanticized nature in a way that can hardly be found anywhere else in Guinea or Ghana, where environmentalism is still quite marginal. In one interview with a former assemblyman who just founded an NGO, this kind of environmental romanticism was quite clearly part of a strategy to link up with Northern environmentalists:

We were having about 22 waterbodies in this community, and AGA has destroyed them all! First, when people went to farm, they didn't go with water. We were living in the forest, … so you went to farm with your small cup … and there was fish in the water! You just put in your trap, you got your fish. You took your gun: monkeys, grass cutter, everything you need you could get it within 10 minutes. So, we were living 13 Bierschenk and Olivier de Sardan (2002: 2) define local development brokers as intermediaries contributing to the influx of external resources from the development sector to a locality, where they play a significant political role, or where they are trying to establish a political standing. They typically run 'projects' at the interface between donors and 'target groups'. See also recent discussions about NGOization (Choudry and Kapoor, 2013). as… as Americans, or your country… Where do you come from? Europe? We were living like Europeans! We were having anything, clean water, good food, fish, meat, everything. We were not having any problem living in this community. So, surface mining has destroyed our life. 14In both Fria and Obuasi, civil-society activism is strongly entangled with political careers, and contrary to their European and American colleagues, educated post-extractivist activists in Fria and Obuasi rarely deviate from neoliberal doxa. Our NGO interviewees mainly insisted on fair democratic elections, transparency, and the liberty of speech. One illustrative example for this world view was the announcement by a member of Fria to create a radio station in Fria 'that is private: belonging to the civil society' (Anonymized, 2018: 128). The most dominant radio in Fria, the 'Voice of Fria', still belongs to the mining company Rusal, and it is, therefore, also private. However, as this also concerns the hospital, electricity generation, the swimming pool, sports courts, etc., the dichotomy of 'private' and 'public' definitely seems to have a different meaning in this setting.

Another common feature of this post-extractivist movement was its insistence on mediation between local authorities and the population. Many of these actors had ties with the company and the state (which has always been in support of industrial mining). Discourse and practice, thereby, often oscillated between radical rejection (and even destruction of company property) and reconciliation. In Guinea, most of the mayors in the mining towns took part in riots, before having been elected or appointed. Not least due to the fact that most of the investment in the 'public good' comes from private actors, their discourse almost became 'schizophrenic' after their installation. This is certainly also connected to the fact that they and their families profited more from CSR measures than average citizens. For instance, the sous-préfet (subprefect) of Mambia, another Guinea mining town controlled by Rusal, had his residence refurnished by the company when the population had taken to the streets because Rusal had not paid its taxes (Anonymized, 2018: 47). The mayor of Kamsar, a third bauxite mining town in Guinea, was sent to the hajj by the mining company, after having taken part in riots. The objective of the company to 'spiritually appease' this mayor with this financial support was openly expressed (Anonymized, 2018: 167). The municipal chief executive of Obuasi took part in galamsey in his youth himself and was then employed by the public-relations department of AGA. While portraying himself as a victim of the company (because it had cancelled a company scholarship due to the death of his father), he very eloquently defends most practices of AGA.

Besides these 'demands for something more' expressed by actors who have actually gained a lot from mining, we were also able to identify numerous resistance movements, mainly in the countryside, which were clearly connected to the consequences of 'accumulation by dispossession'. This resistance comprised roadblocks and other sit-ins, the destruction and the theft of tools and machines, illegal mining, and the physical assault of company personnel. In Obuasi, the most important trigger for closure was the death of the head of communications of AGA, John Owusu, during an operation against illegal miners. Owusu is reported to have been run over by a company vehicle, while running away from enraged illegal miners (The Ghanaian Times, 2016). In Sanso, one of the villages around Obuasi that was strongly impacted by mining, violent conflict is still recurrent, and many interviewees warned us not to enter the village because 'criminals' lived there and could confuse us with company staff and attack us. When we went there, we were told a very different story. The population argued that it had been 'forced into galamsey' because mining had destroyed their livelihood. 15Respondents explained that state and corporate repression led to several deaths and injuries in recent years, for instance by the use of guard dogs to chase 'illegal miners' (cf. Commission on Human Rights & Administrative Justice, 2008). Similar movements happened in the cities' shanty towns, whose population had strongly depended on the purchasing power of the workers and profited from a wide range of services of the company that were provided on a voluntary basis, like electricity, semi-public transport, waste disposal, etc. In the months that followed mine closure in Fria, demonstrations and clashes with police and gendarmerie caused several deaths (Anonymized, 2018: 118). People also took the streets because of water shortages, the insufficient maintenance of apartments, the end of waste treatment, insufficient health care, and pollution (Field research, 2017). In addition, many contract workers profited from illegal trade with subsidized food packages, petrol, and medicaments, which continued after closure as part of the 'care and maintenance' measures of Rusal. People also started to dismantle the factory in search for saleable parts, like, for instance, cables. This systematic theft also concerned fuel, which has always been an important additional income in many Guinean company towns. According to a former accountant of Rusal, 70 per cent of all the expenditure of the company in Fria was spent on fuel, but there was 'total opacity' about the use of it (Anonymized, 2018: 120). When authorities tried to stop this illegal trade in November 2012, seven months after mine closure, people openly attacked the investigators, set their cars on fire, and ravaged their houses, destroying potential evidence about illegal trade with fuel. These actions seem to have been backed by the military (Anonymized, 2018: 120).

Most of these acts of resistance could be depicted as 'silent' movements, in the sense that they had no spokesperson and manifested themselves mostly in direct physical action. However, this does not mean that they were less effective. For instance, mainly due to such actions, Fria has received a connection to the national grid in August 2015, after three years of opacity. In Obuasi, due to the pressure of small-scale miners, AGA has recently restituted 60 per cent of its concession to the government, which will hand over these claims to galamsey (Odonkor, 2016).

CONCLUSION

In this article we have approached mine closure in Africa from the perspective of 'the right to the city'. Compared to the political circumstances of Paris in the 1960s, when Lefebvre invented the slogan of the 'right to the city', movements led by of educated groups in the two analysed mining towns could be described as rather pragmatic. This has also been observed in shrinking cities in Europe and the US (Souza, 2010: 316) and has several reasons, including the (inter)national historical context, the size of these cities, the effects of depoliticization of overall corporate control, and the special position of African miners in terms of class relations. As a result, both in Fria and in Obuasi, the return of industrial mining would certainly be acclaimed by the majority of the population, even if its long-term social, political, and environmental consequences have been far from positive since the beginning of mining in the two countries. However, around both cities, peasant movements have strongly gained momentum after mine closure. Renewed industrial mining will, therefore, be confronted with fierce resistance from petty miners and farmers, who have regained their claims and land, and will be even more reluctant to give way again. Marcuse (2012: 38) differentiates between demands and aspirations for a right to the city: 'The demand comes from those directly in want, directly oppressed, those for whom even their most immediate needs are not fulfilled.

… The aspiration comes rather from those … constrained in their opportunities for creative activity, oppressed in their social relationships, guilty perhaps about an undeserved prosperity, unfulfilled in their lives' hopes.' To him, both could rally behind a common goal: 'Eliminating profit as means and motivation in the political sector [and] eliminating the role of wealth and the power linked to it from public decisions' (ibid).

Marcuse's description of the 'aspirations for a right to the city' certainly aims at inhabitants of industrialized countries and can only be partly translated to African contexts. African 'labour aristocracies' have even less to do with historical aristocracies than their European counterparts of the late 19 th century, for whom the term was created, and only a small part of these mineworkers are able to take part in the 'imperial way of life' (Brand and Wissen, 2017). However, as we have seen, we can also differentiate in these cities between 'demands' and 'aspirations', and in the case of Obuasi, the strong support of city dwellers for petty gold miners in and around the mines shows how an association of 'demands ' and 'aspirations' could work out (cf. Peprah 2017). This could also serve as an example for similar 'corevolutionary movements' (Marcuse, 2012: 38) on the national and even the international scale, where a convergence of degrowth and post-extractivist movements still seems to be unthinkable (Brand, 2015: 19).

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Figure 1 .Figure 2 .

 12 Figure 1. Actual annual receipts of the Obuasi Municipal Assembly from 2010-16 in US$ (converted from GHS based on annual exchange rates)

This is not to say that the concept has not been applied to Africa. See e.g. Huchzermeyer

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However, the history of gentrification in cities like New York or Berlin also showed how fast this 'degrowth euphoria' can turn into the opposite: Due to their high cultural and societal valorization, such spaces of social experimentation can quite swiftly become places of renewed surplus absorption (see e.g.Marcuse, 1986).

This processing plant and the adjacent mine have resumed production in July 2018(Guèye, 2018). Fria thus seems to enter a renewed boom phase.

Interview, street vendor, Obuasi, 18 June 2017.

Interview, shop owner, Obuasi, 18 June 2017.

Interview, former employee of AGA, Obuasi, 17 June 2017.

Interview, director of AGA's school, Obuasi, 13 June 2017.

Interview, AGA socioeconomic development planner, Obuasi, 17 June 2017.

Interview, director of AGA's school, Obuasi,

June 2017.

Interview, former assemblyman, Sanso/Obuasi, 18 June 2017.

Interview, former assemblyman, Sanso/Obuasi, 18 June 2017.

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Qiushi Cao
email: qiushi.cao@insa-rouen.fr

Cecilia Zanni-Merk

Christoph Reich

Towards a Core Ontology for Condition Monitoring

Keywords: condition monitoring, state of the system or machine, ontology engineering, core ontology, conceptual model

Condition monitoring is performed to identify the functioning state of a machine or a mechanical system. It is an important task by which the machine or mechanical system deterioration tendency and the location of a failure can be detected. In recent years, ontologies have shown promising results to enhance knowledge sharing in condition monitoring tasks, while offering a logically defined and controlled vocabulary of domain entities. Motivated by the growing demand for unification and formal representation of useful concepts in condition monitoring, in this paper we present CM-core, an ontology of core condition monitoring entities. It incorporates several ISO standards as sources and also extracts general concepts from a series of domain ontologies. The ontology contains taxonomies of core condition monitoring concepts such as system, function, behavior, structure, state, failure and fault, with their interrelationships. The CM-core ontology has a broader domain coverage than the existing ontologies, and its generality ensures further specification into more specific domain ontologies.

Introduction

Condition monitoring is a key technique for assuring the proper functioning of machines or mechanical systems. Generally aligned with fault diagnosis tasks, condition monitoring and maintenance has appealed to deep attention from domain experts and engineers. In the context of Industry 4.0, during the machine or mechanical system life cycle, condition monitoring activities are performed by obtaining data from sensors that are located at the components of the machines or mechanical systems, for identifying their operating state.

According to the current state, if any fault or failure exists, a diagnosis can be launched to determine the causes of it. Also, based on the characteristics of the fault or failure, analysis about how they will propagate and evolve over time can be performed. The use of condition monitoring techniques has several advantages, such as improved machine availability, improved production efficiency, and reduced maintenance cost [START_REF] Widodo | Support vector machine in machine condition monitoring and fault diagnosis[END_REF][START_REF] Rao | Handbook of condition monitoring[END_REF].

Recently, machines are connected building cyber-physical systems (CPSs), which are a new class of engineered systems that offer close interaction between cyber and physical components [START_REF] Khaitan | Design Techniques and Applications of Cyberphysical Systems: A Survey[END_REF]. As the CPSs become more and more complex, the knowledge required for system operation and maintenance increases in complexity. In this context, the need for standard and well-defined models for capturing this complex knowledge is in high demand [START_REF] Prestes | Towards a core ontology for robotics and automation[END_REF]. Ontologies have had great success with facilitating the formalization of condition monitoring tasks in different domains [START_REF] Papadopoulos | Wind turbines' condition monitoring: an ontology model[END_REF][START_REF] Nandi | Condition monitoring and fault diagnosis of electrical motors A review[END_REF][START_REF] Nuez | An ontology-based model for prognostics and health management of machines[END_REF]. Ontologies are knowledge models that represent formal, flexible and inter-operable representations of domain concepts. The use of ontologies can streamline the data exchange among different systems, provide services for answering queries about those data, and offer services to improve the interoperability among heterogeneous systems [START_REF] Panov | Ontology of core data mining entities[END_REF].

However, most of the existing ontologies that are used to facilitate condition monitoring tasks are domain-specific, which means that they contain very specific domain concepts and properties, thus not feasible of being reused if the domain of interest changes. Taking account of this, in this paper we present a core ontology, named CM-core. The ontology contains basic concepts, properties, and relationships that are general across a variety of monitoring domains. The development is based on a series of ISO standards and domain ontologies. The generality of the ontology ensures the further specification into more specific domains. By formalizing domain concepts and relationships, the ontology captures and structures manufacturing domain knowledge and makes it usable by an intelligent CPS. The goal of such an intelligent CPS is to facilitate condition monitoring tasks in manufacturing, by providing intelligent decisions about machinery fault or failure prognostics and maintenance plans.

The remainder of the paper is organized as follows. In Section 2, we present related work, in which a set of existing ontologies related to condition monitoring will be discussed. Section 3 shows the design approach for the ontology, as well as the key classes and properties of it. Section 4 presents the conclusion and future perspectives.

Related work

There exist several ontologies and conceptual models related to condition monitoring. These efforts mainly focus on providing formal representations of concepts such as system, fault, failure, alarm, and measurement, in different specific domains. In this section, we first enumerate some of the most related ontologies and conceptual models existing in the literature.

• The ontology for condition assessment of a power substation apparatus [START_REF] Feng | Condition assessment of power system apparatuses using ontology systems[END_REF] was developed to be one segment of the power system ontology [START_REF] Feng | An ontology for knowledge representation in power systems[END_REF]. By modeling key concepts of a partial transformer, the authors argue that this ontology can be used to support a range of important processes such as transformer thermal condition monitoring, remote monitoring and dissolved gas analysis [START_REF] Feng | Condition assessment of power system apparatuses using ontology systems[END_REF].

• Ontoprog is an ontology developed to model the knowledge related to Prognostics and Health Management (PHM) of machines [START_REF] Nuez | An ontology-based model for prognostics and health management of machines[END_REF]. The authors stated that this ontology could be used to address failure analysis tasks in the context of smart manufacturing. Being used in a real centrifugal pump condition monitoring, the ontology showed its robustness regarding future decision making for condition-based maintenance in real processes [START_REF] Nuez | An ontology-based model for prognostics and health management of machines[END_REF].

• The ontology for wind energy [START_REF] Kk | Semi-automatic construction of a domain ontology for wind energy using Wikipedia articles[END_REF] was developed through a semi-automatic ontology construction process. In the process, the authors used an approach in which the concepts and properties of the ontology were learned from related Wikipedia articles. As an outcome, the frequent phrases were extracted and organized into classes and properties.

• A railway ontology introduced in [START_REF] Umiliacchi | Predictive maintenance of railway subsystems using an Ontology based modelling approach[END_REF] aims to model contextual information, and also improve the diagnostic performance. The ontology incorporates important concepts in railway subsystems such as system status, symptom, observations, and fault. The developed ontology-based systems have shown satisfactory results in assisting with rolling stock, infrastructure, train operation and traffic management [START_REF] Umiliacchi | Predictive maintenance of railway subsystems using an Ontology based modelling approach[END_REF].

• An ontology for modeling the integration of Intelligent Maintenance Systems (IMS) and Spare Parts Supply Chain (SPSC) was introduced in [START_REF] Da Silvaand | Building an Ontology for Intelligent Maintenance Systems and Spare Parts Supply Chain Integration[END_REF]. This ontology fulfills the need of a common vocabulary for achieving a proper integration from IMS to SPSC, thus improves the quality of demand prediction in a SPSC.

The ontologies listed above cover specific concepts and properties in certain domains. The scopes of these ontologies are limited in domains such as wind energy, railway system, and supply chain management. Hence, they suffer from the issue of very specific coverage. When researchers or engineers are confronted with an issue in a different domain, a new model for the formal representation of domain concepts may need to be designed, since the existing ontologies do not model sufficient knowledge. The development of a new model may be time-consuming and require a lot of resources. To this end, representations of condition monitoring concepts and properties as general as possible, enabling easy extension and specification for a wide range of domains, tasks, and applications is needed. This is our motivation for developing CM-core, a core ontology for condition monitoring that is presented in Section 3.

The CM-core ontology

In this section, we present the CM-core ontology. During the development phase, we adapted the iterative ontology development process introduced in [START_REF] Noy | Ontology development 101: A guide to creating your first ontology[END_REF], and took profit from three knowledge sources: (i) ISO standards 13372 [START_REF]Condition monitoring and diagnostics of machines Vocabulary[END_REF], 9000 [START_REF]Quality management systems Fundamentals and vocabulary[END_REF] and 9001 [START_REF]Quality management systems --Requirements[END_REF]; (ii) the domain ontologies mentioned in Section 2, and (iii) relevant research papers and textbooks, such as [START_REF] Schreiber | Knowledge engineering and management: the CommonKADS methodology[END_REF] and [START_REF] Kaposi | Systems for all[END_REF]. In the following subsections, we first introduce the general architecture of the CM-core ontology and then enumerate the core classes with their relationships among each other.

General architecture

The CM-core ontology aims to cover general concepts in condition monitoring that are common to many subdomains. To permit generality, the formal representation of key condition monitoring entities in the CM-core ontology has been made as generic as possible. In this subsection, we provide the terms that will be associated with the classes of the ontology. The CM-core ontology has been aligned to UFO [START_REF] Guizzardi | Using the unified foundational ontology (UFO) as a foundation for general conceptual modeling languages[END_REF], which is an upper-level ontology. We show how the CM-core ontology classes are aligned to UFO, and the general formal architecture of the ontology is presented thereafter.

• System: Set of interrelated elements that achieve a given objective through the performance of a specified function [START_REF] Stevens | Engineering mega-systems: The challenge of systems engineering in the information age[END_REF]. We refined the definition of the class Ontoprog: System in [START_REF] Nuez | An ontology-based model for prognostics and health management of machines[END_REF], by using a qualitative characterization model called Structure-Behavior-Function (SBF) [START_REF] Goel | Structure, behavior, and function of complex systems: The structure, behavior, and function modelling language[END_REF]. This class has been aligned with the Object class in UFO, through the alignment CM-core: System ⊑ UFO: Object.

In UFO, Object (Endurant) represents a set of entities that posses spatial-temporal qualities. In CM-core, the System class contains different kinds of physical systems in the manufacturing domain, and they all obtain spatial-temporal qualities. Thus, the above alignment is proposed.

• Process: Set of interrelated or interacting activities that use inputs to deliver an intended result [START_REF]Quality management systems --Requirements[END_REF]. This class has been aligned with the Complex Event class in UFO, through the alignment CM-core: Process ⊑ UFO: Complex Event.

In UFO, a Complex Event (Perdurant) stands for a set of combined events with each consists of at least two single events. The Process class in CM-core represents manufacturing processes that are structured as a series of simple activities. For this reason, the above alignment is proposed.

• Parameter: Variable representing some significant measurable system characteristic. The value of a Parameter is measured by sensors that are located at different components of the System. When the domain changes, different Parameters could be selected for the condition monitoring task, such as bearing temperature, oil debris, oil pressure, velocity, voltage, .etc. The alignment for this class and the upper-level UFO class is CM-core: Parameter ⊑ UFO: Moment.

In UFO, the Moment class (Endurant) is a set of individuals that are existentially dependent on individuals of Object, such as color, height and electronic charge. In CM-core, we also define the a Parameter to be existentially dependent on a System. Thus the proposed alignment is valid.

• State: The condition of a System at a specific time. The condition of a System is associated with the values of a set of Parameters. Since a State is existentially dependent on a System, the alignment CM-core: State ⊑ UFO: Moment has been proposed.

• Behavior: It is represented as a sequence of States and transitions among them. The States together with transitions specify the evolution in the values of the Parameters [START_REF] Goel | Structure, behavior, and function of complex systems: The structure, behavior, and function modelling language[END_REF]. According to the definition, the Behavior of a System is also existentially dependent on a System. Therefore, the alignment CM-core: Behavior ⊑ UFO: Moment has been introduced for the CM-core ontology.

• Fault: A Fault is defined as a condition of a System that occurs when one of its components or assemblies degrades or exhibits abnormally [START_REF]Condition monitoring and diagnostics of machines Vocabulary[END_REF]. The representation of this class is adapted from Ontoprog: Fault [START_REF] Nuez | An ontology-based model for prognostics and health management of machines[END_REF], with slight modification. Based on the definition, we propose the alignment CM-core: Fault ⊑ UFO: Event, for representing a Fault as an Event (Perdurant) that happens in time.

• Failure: Termination of the ability of an item to perform a required function [START_REF]Condition monitoring and diagnostics of machines Vocabulary[END_REF]. A Failure is a manifestation of a Fault. We adapted the definition of the class Ontoprog: Failure [START_REF] Nuez | An ontology-based model for prognostics and health management of machines[END_REF], with minor alteration. We also align this class with the UFO class Event, through the alignment CM-core: Failure ⊑ UFO: Event. Based on these terms, the classes with their object properties and data properties are constructed. A class defines a group of individuals which share some properties, and individuals are instances of the class. Object properties are binary relations between individuals, and data properties can relate individuals to concrete data values. Fig. 1 shows the global architecture of the CM-core ontology. For the purpose of clarity, we only show part of the classes and properties. In Fig. 1, rectangles are classes, solid lines represent object properties between classes.

The "Hermit" reasoned [24] is used to check the consistency of the ontology. The ontology has been evaluated by the experts, for its

Conclusions and future perspectives

In this paper, an ontology that models the core concepts and properties for condition monitoring, named CM-core, has been introduced. The ontology contains core concepts related to condition monitoring, such as system, structure, behavior, function, state, fault and failure. The generality of the CM-core ontology ensures the possibility of its specialization into more specific domain ontologies, such as the ontologies for machine condition monitoring in industry. Thus, the CM-core ontology can be extended and customized to satisfy better the needs in individual domains where ontologies need to be used to empower information systems.

Future works will include the extension of the ontology for prognostic purposes. Machinery prognosis is an important aspect of condition monitoring, whose aim is to predict the fault conditions before they occur. To do this, the CM-core ontology will be specialized for the manufacturing domain, to be integrated into an intelligent system [START_REF] Yam | Intelligent predictive decision support system for condition-based maintenance[END_REF]. In the intelligent system, a rule base is needed to perform reasoning, for launching alarms about possible occurrences of machinery faults in the future. This rule base can be elicited by mining sensor data, which will learn normal and abnormal behaviors of the machinery. The intelligent system aims to detect fault conditions and trend of failures of the machinery, thus facilitate decision making such as launching fault/failure alarms and providing maintenance plans.

Fig. 1 .

 1 Fig. 1. Global architecture of the CM-core ontology.

Acknowledgements

This work has received funding from INTERREG Upper Rhine (European Regional Development Fund) and the Ministries for Research of Baden-Wrttemberg, Rheinland-Pfalz (Germany) and from the Grand Est French Region in the framework of the Science Offensive Upper Rhine HALFBACK project.