Intangibility

Unlike physical products, services cannot be experienced through the senses before being consumed. ^{Robert et al. (1989)} mentions that anyone who buys a service can leave empty-handed, but will never leave empty-headed, referring to gaining experiences through the provision of a service.

Inseparability

Both the service provider and the client or tourist must be present for the service to be provided. The inseparable nature of the service means that tourists are an indispensable part of the product.

Variability

The quality of service depends at all times on who, when how and where the service is provided. In this sense, the lack of homogeneity in the product can be the main cause of disappointment in tourists, or on the contrary, it can help to offer services tailored to each visitor.

Perishable nature

The services are not stored or saved to be used later, they are extinguished with their provision, so that unsold stocks cannot be stored.

The tourism services offered by travel agencies, hotels, restaurants, tourist guides, etc., cannot be seen or touched by tourists, despite seeing or touching some of the tangible elements of the tourism product (^{Zeithaml et al., 2009}). These are produced and consumed at the moment, both by the service providers and the tourists themselves, therefore, the satisfaction of the client or tourist is determined by the quality of the services acquired throughout their stay in the destination.

As mentioned above, the quality of service to tourists is the key to achieving success within the competition demanded by this globalized world. Tourists are more informed people with higher education who demand quality in the services offered, therefore, customer loyalty is, perhaps, the best way to measure quality. The ability of a service company to attract and retain customers will depend to a large extent on the added value it offers them (^{Kotler, 2011}).

Now, service quality is closely linked to the value chain, which works as an innovative and useful tool to identify the factors that drive or condition the generation of value in a tourist destination and in each of its links (^{Pulido and López, 2016}). Therefore, it should not be forgotten that behind each tourism service is a technological system that supports it, in addition to having a value chain that is made up of suppliers until reaching the final customer (^{Izaguirre, 2015}).

Regarding the concept of value chain, it was created and disseminated by ^{Porter and Millar (1985)}, who defined value as the amount that the buyer is willing to pay for a product offered by the company. The value activities for a company, according to Porter, are made up of nine activities, the first five are primary, which involve the physical creation of the product (inbound logistics, operations, outbound logistics, marketing and sales, services) and four support activities which support the primary activities (company infrastructure, human resource management, technological development and procurement) (Porter and Millar, 1985).

In this regard, ^{Alonso (2008)} mentions that the value chain proposed by Porter, despite focusing directly on tangible aspects, can be adapted to the provision of services. Continuing with some other definitions, the set of main activities of a company, which are linked through links, is called value chain, as the product goes through each of these activities it adds its value (^{Kippenberger, 1997}).

Under this same perspective, a simple value chain describes the full range of activities that are required to carry a product or service from its conception, through the different phases of production (involving a combination of physical transformation and the contribution of several producer services), delivery to final consumers and final disposal after use. (^{Kaplinsky and Morris, 2001}). The number of links in a value chain depends on the type of industry. These can sometimes be carried out by one company and sometimes by several (^{Kaplinsky, 2000}).

For the ^{Food and Agriculture Organization of the United Nations (FAO) (2006)}, a value chain is like a network or strategic alliance that is established, formally or informally, between a number of independent business actors participating within one or more production chains. For the ^{German Agency for Technical Cooperation (GTZ) (2007)}, a value chain is defined as: ‘an economic system made up its operators, providers of operational services and their commercial links at the micro level, and by the providers of support services at the meso level. All operators that add value to a given marketable product, starting with the raw material until reaching the final consumer, are considered part of the value chain’.

This methodological approach of ValueLinks created by the German Agency seeks sectoral economic development at the local, national and global level, through the promotion of value chains for the benefit of the population with fewer economic resources, with a focus on pro-poor growth (CPP). This approach is based on the premise that the economic growth of poor people in markets provides a sustainable solution to the problem of poverty (^{GTZ, 2007}).

In the manual ValueLinks, of the German agency for international cooperation (GTZ for its acronym in German), a distinction of four actors that participate in the value chains is made: in the first place, there are the operators of the value chain formed by the private sector as protagonists of the chain, in the second place, there are the providers of services and support such as chambers and technological institutes, organizations of the academic sector or universities. As a third element is the public administration to create favorable conditions for economic development, and finally there are the development agencies and NGOs to boost, promote, and support the rest of the agents of the value chain (^{GTZ, 2007}).

Therefore, the understanding of value chains with a focus on tourism allows organizing the tourism sector in which the suppliers of all the products and services that are part of the experience that the tourist will live, from the planning of the trip, the permanence in the destination and selection of services, until reaching their place of residence. For researchers and professionals in the sector, it helps to identify those value chains in which local, national and global actors can produce better products and services, increase job creation and in many cases, reduce the poverty experienced in most developing countries. Finally, the research and subsequent implementation of this issue is of vital importance to generate tangible changes and improve the distribution of income and benefits in the communities that participate in tourism activity.

Once the search for scientific papers was carried out, different aspects of them were analyzed, which are detailed below: The interest in the subject of value chains focused on tourism services is shown by ^{Ortíz (2001)} when publishing his research Estia-efficient electronic services for tourists in action, so that from that year the writings have been gradually increasing. Considering the 10 retrospective years for this analysis, it is found (Figure 1) that the highest peaks in publications occurred in 2019 and 2020 with seven and nine documents respectively. The health emergency due to the COVID-19 virus has hit the tourism sector hard, so it has become a necessity to do research on how to improve and adapt tourism activity to the ‘new normal’.

Figure 1 Number of documents written per year (2010-2020). Elaboration with data from http://www.scopus.com. 

Authors who have publications on related topics related to CVT are broken down in Figure 2. In this a list of 12 authors who have two research papers can be seen, some as the sole author and others in collaboration with other researchers. For example: ^{Adiyia and Vanneste (2015} and ²⁰¹⁸⁾ have jointly published works. It is the same case for Casarin et al. (2014) by having two collaborative works. Halpern and ^{Mwesiumo (2016} and ²⁰¹⁸⁾ collaborated on two papers. Okolo-Obasi and ^{Uduji (2019} and ²⁰²⁰⁾ worked in collaboration with other authors and finally ^{Anderson (2017} and ²⁰¹⁸⁾ has an investigation as the sole author in 2018 and another in collaboration in 2017. The only one who has two published contributions as the sole author is ^{Kaewkitipong (2010a)} and (^2010b), although the title of the research is the same.

Figure 2 Authors of papers on tourism value chains. Elaboration with data from http://www.scopus.com. 

Knowing the affiliation of the published research papers is important, since it allows identifying the educational institution to which the researchers belong, which could be an option for future collaborations regarding CVT topics. In this regard, Figure 3 shows the affiliation of the researchers. First, there is the University of Innsbruck, one of the oldest in Austria, followed by Thammasat University, Bangkok’s second oldest university in Thailand. In third place is the Ca’Foscari University, Venice’s main university in Italy.

Figure 3 Documents by affiliation. Elaboration with data from http://www.scopus.com. 

On the list there are two Norwegian universities, one of them is Molde University (Høgskolen i Molde) and the other is Kristiania University College, one of the oldest private institutions of higher education located in Oslo. Finally, there is KU Leuven, Belgium’s largest and best-positioned university, a leader in research and co-founder of the League of European Research Universities (LERU) and the University of Nigeria in Nsukka, Nigeria.

The leading country on scientific research that addresses topics related to tourism value chains is Thailand, having the largest number of written documents (two in 2010, one in 2015 and recently published two in 2020), followed by China with four investigations (one in 2013, two in 2014 and one in 2019) as well as South Africa (three in 2018 and one in 2019). Denmark has three writings, as well as Italy, Norway and the United States of America published in different years (Figure 4).

Figure 4 Countries with the highest number of investigations on CVT. Elaboration with data from http://www.scopus.com. 

It should be noted, in this section, that of the nine contributions made this 2020 with topics related to CVT, these belong to countries such as Colombia, Germany, South Korea, Spain, Switzerland, Italy, Nigeria and again the countries that are among the top ten in publications are India and Thailand.

As a special mention, the contribution made by Latin American countries is recognized (Figure 5), since despite being minimal, their scientific production in relation to the CVT topic serves as a reference for future research within the Latin American context. One of them is the one made in Ecuador by ^{Rendón and Bidwell (2015)}, which is a book chapter entitled ‘Success in progress? tourism as a tool for inclusive development in Peru’s Colca Valley’, with affiliation in the Latin American Faculty of Social Sciences in Quito and the Victoria University of Wellington, Wellington, New Zealand.

Figure 5 Latin American countries with studies on CVT. Elaboration with data from http://www.scopus.com. 

It is followed by Argentina with the paper by ^{Castillo et al. (2017)} title: ‘The causal effects of regional industrial policies on employment: a synthetic control approach’. The institutions of affiliation are the observatory of employment and business dynamics, ministry of labor, University of San Andrés and Inter-American Investment Corporation.

Finally, a recent contribution from Colombia is made by ^{González and Husain (2020)} with the written work entitled ‘Social entrepreneurship and sustainable tourism in Colombia: a baseline study in post-conflict regions’. Affiliation with the La Salle University and University Corporation God’s Minute, both in Bogotá Colombia.

With respect to the type of written documents related to CVT, there is a record of 36 scientific papers (71%), followed by seven book chapters (13%), five conference papers (10%) and finally with a book, a note and a paper under review with 2% respectively (Figure 6).

Figure 6 Type of publications related to CVT. Elaboration with data from http://www.scopus.com. 

The thematic area of the writings allows knowing which is the area to which the researchers interested in developing topics related to CVT belong (Figure 7). In this regard, it is shown that the area of business, management and accounting is the most interested, having 41%, which is equivalent to 43 writings. The social sciences registered 30%, which means 31 writings. It is important to highlight this area of knowledge since tourism belongs to it and in which a variety of research has been formulated. Economics, econometrics and finance is another of the areas interested in the subject of CVT, which examined 8%, resulting in nine documents. An area that has developed in this theme is environmental sciences, since it is sought that tourism activities are developed based on the principles of sustainability, so it registered 7% with seven documents. Finally, computer science, arts and humanities, as well as engineering, exact sciences, energy and mathematics register an interest in the subject, although in a smaller percentage.

Figure 7 Documents by thematic area on CVT. Elaboration with data from http://www.scopus.com. 

To conclude with the analysis of graphs, there are the most requested journals to publish topics related to CVT. In this regard, it is shown that the African Journal of Hospitality, Tourism and Leisure is the most popular, having six documents between 2018 and 2020, followed by Tourism Review with 1 document in 2016 and two in 2017. Development Southern Africa with two documents (2010 and 2018). Although the Journal of Tourism and Cultural Change only has two publications, both are current since they belong to 2019 and 2020. Tourism Planning and Development and Wit Transaction on Information and Communication Technologies have two writings each published between 2010 and 2018 (Figure 8).

Figure 8 Documents published by year and by journal. Elaboration with data from http://www.scopus.com.