## 4 Literature Review and Related Work
### Distributed Ledger Solutions (2016-Today)  
Following the first electronic traceability systems for agriculture products described above, and as the blockchain technology was maturing and becoming more mainstream in other application domains, more and more research efforts emerged, concentrating on the use of DTL for agriculture traceability systems. [PERSON] (2016) proposes a revolutionary idea about a system based on RFID and blockchain technology for Chinese agri-food markets with the aim of enhancing their food safety and quality, as well as reducing losses during logistic processes [10]. [PERSON]'s work is one of the most cited in the literature regarding blockchain applications in the agriculture sector. According to [PERSON], RFID and blockchain technology are used to guarantee food safety and quality throughout the entire supply chain. The paper examines two types of agriculture products: (i) fresh fruits and vegetables, and (ii) meat, such as pork, chicken and beef. The proposed network utilizes the features of blockchains so that all stakeholders can have access to every transaction and information regarding a specific product. The basic aim of [PERSON] is to cover the whole process of data collection and information management, for every transaction between the stakeholders in the agriculture supply chain. The entire system provides monitoring, tracking and tracing of the quality of agri-food and can be characterized as a \"farm to fork\" solution. [PERSON]'s solution presents both advantages and challenges (considering societal, financial and technical aspects) compared to centralized solutions. [PERSON] (2016) proposes an ontology-driven blockchain traceability system. The main idea of [PERSON] is to translate and define some crucial traceability components as different ontologies. Similarly with [PERSON] (2016), [PERSON] utilizes blockchain technology in order to propose a traceability system with various ontologies, where each one could accomplish and be part of certain transactions. Alongside blockchain technology and ontologies, [PERSON] proposes the use of smart contracts. The platform used in this paper is Ethereum, programmed with the Solidity programming language [83]. [PERSON] et al. continue their research in 2017 and propose a blockchain solution for agriculture traceability in order to ensure that the HACCP principles and requirements are addressed during the production, transportation and preservation of a product [36]. Moreover, [PERSON] et al. (2017) focus on the increasingly serious problem of food safety in China and proposes a blockchain solution for the agriculture supply chain, based on information and transaction security between all the involved parties. In this paper, a PEST (political, economic, social, technological) environment analysis is presented in order to define the challenges and the opportunities of the DLT solution [84]. [PERSON] et al. also propose a blockchain solution focusing on the animal products supply chain in Italy [59]. They conduct an analysis of the animal products supply chain in order to identify the discrete steps of tracking and tracing a product. Additionally, in the context of different scenarios, they study the way in which the number of involved parties at each supply chain step could affect the complexity level of information flow. In this direction, [PERSON] et al. propose a blockchain framework which can help to improve tuna traceability and stop illegal and unsustainable fishing practices [67]. Considering the safety of agriculture products, [PERSON] et al. [41] propose a rice supply chain system that uses blockchain technology to assure the safety of rice during its flow through the supply chain. The growing research interest in blockchains and traceability in agriculture gained further ground in 2018 when many research efforts on this issue were published. [PERSON] et al. discuss a dual chain solution for the agriculture supply chain.