## 4 Literature Review and Related Work
### Distributed Ledger Solutions (2016-Today)
[PERSON] and [PERSON] also refer to the evolution of blockchain technology in which data will no longer be stored in blocks but as a directed acyclic graph (DAG). Through this approach, it is estimated that data can be processed much faster, which could address the scalability problem of throughput, latency and capacity regarding the execution of transactions. In the same context, [PERSON] et al. conduct a thorough analysis in order to model a blockchain enabled traceability system in the agriculture supply chain. Through interpretive structural modeling (ISM) and decision-making trial and evaluation laboratory (DEMATEL) methodologies, [PERSON] et al. establish hierarchical levels and relationships between the involved actors in the supply chain [32]. The study identifies thirteen enablers for implementing blockchain technology in agriculture supply chains, such as anonymity and privacy, immutability, smart contracts, secured and shared database, traceability, transparency, and others; the enablers were validated by agriculture supply chain experts. The authors also highlight the need to further involve experts from various countries in order to ensure consideration of diversity factors and relevant indicators. Another interesting idea in this direction, presented by [PERSON] et al., describes a blockchain-IoT based system which utilizes the proof of object (PoO) concept as an alternative to the blockchain's proof of work (PoW) and proof of stake (PoS). PoO is a validation method where the owner of the object is obliged to prove the possession. As long as the other stakeholders validate this claim, a consensus is reached and a new block is added in the blockchain. The authors follow an analytical approach and present trial results for the proposed model regarding the implementation of the consensus algorithm, the security issues and the involved sensor technology [61]. In 2019, important similar studies focusing on the application of blockchains in agriculture traceability systems appear. [PERSON] et al. in [PERSON] et al. (2020) propose a safety management system for tea quality, based on a public Ethereum blockchain. Moreover, [PERSON] and [PERSON] in [PERSON] and [PERSON] (2019) present a general architectural concept for blockchain implementation in agricultural product traceability systems. [PERSON] et al. [PERSON] et al. (2019) describe a blockchain application in a rice supply chain, with the aim of changing the way in which the food corporation in India manages the supply chain, as well as enabling significant wastage reduction. Furthermore, several studies present concepts and implementations of blockchain-based traceability systems regarding different agricultural products, such as chicken [PERSON] and [PERSON] (2019), bananas, fish and meat [PERSON] and [PERSON] (2019), maize [PERSON] and [PERSON] (2019), and pork [PERSON] and [PERSON] (2019). The upward trend of research interest regarding blockchain and agriculture is depicted in Figure 2 below, which demonstrates the trend of Scopus documents with the search term TITLE-ABS-KEY(agriculture AND blockchain) from 2017 to 2019. The research interest in this specific domain continues to grow also in 2020. [PERSON] et al. [PERSON] et al. (2020) present a conceptual architecture to store high-throughput crop breeding data, in an efficient and safe manner, by using blockchain technology in a breeding information management system. Furthermore, [PERSON] et al. focus on the potential arising from DLT in the smart farming initiative, due to more transparent, safe and efficient data sharing [PERSON] et al. [PERSON] et al. (2020) study the effect transaction costs reduction due to the use of a blockchain as a DLT in grain trading in Australia. Table 3 depicts the classification of relevant research works regarding the use of blockchain technology in agriculture traceability systems, according to the agriculture sector and product.