## 2 Conceptual Framework of AgroTRACE
### Sharing  
One of the key challenges of the existing traceability systems is their interoperability and data sharing, as they both allow for smooth information exchange when it comes to trade transactions. Towards this direction, the GS1 interface standards listed below are used:  
* Global Data Synchronization Network (GDSN): It links the trading partners with GS1 Global Registry through GS1 certified data. This provides the capability of instant electronic exchange of updated, standardized and verified information. Furthermore, the useful information can be shared pertaining to GTINs; unique identity for the owner's product, description of the product, and classification of the product in terms of Global Product Classification (GPC). * Electronic Data Interchange (EDI): It enables the exchange of important documents between enterprises via a standard format. It can also allow for sharing information including GTIN, GLN and SSCC, which were briefly described above, as well as invoicing, delivery information, order details and payment tracking. * Electronic Product Code Information Services (EPCIS): It is the standard for the information exchanging dealing with critical events about the monitoring of the route of a product taking place along the agri-food supply chain. It also shares information such as the date, time and location in the action stream of the event of interest, GTIN and GLN. The framework of the AgroTRACE system described above, along with the implemented standardization throughout the agri-food supply chain, is illustrated in Figure 2. The implementation of GS1 standards is an essential aspect of AgroTRACE system for the purpose of being fully modular and able to receive and send information by utilizing IoT technologies and event capturing applications (e.g., QR, RFID and Barcode readers). As can be inferred from this graph, the ability for traceability is extended beyond the farm-to-shelf route covering also the recycling and industrial symbiosis; the waste of a production process becomes an input for another unit. This realization takes place in the framework of the circular economy context. In this context, the proposed integrated system enables traceability of organic waste by providing the required documentation about the Corporate Social Responsibility to the supply chain partners. An important strength of AgroTRACE is both the big data collection and management in real conditions covering various stages of the supply chain from farm-to-shelf-to-farm. As far as big data management is concerned, the open source Apache Hadoop software [62] is used that enables distributed processing of big data in computer clusters by utilizing relatively simple programming models. This software has been created as a means of scaling up from single servers to a plethora of machines, each one providing localized computation and storage. Rather than depending on hardware for offering high availability, the library has been designed to find out and address failures on the application layer. The Apache Hadoop project includes the following modules [62]: (a) \"Hadoop Common\" providing the common utilities which support the other modules, (b) \"Hadoop Distributed File System\", which is a distributed file system offering accessibility to application data, (c) \"Hadoop YARN\", offering a system for cluster resource management and job scheduling, (d) \"Hadoop MapReduce\" enabling parallel processing when it comes to large data sets, and (e) \"Hadoop Ozone\", which is a scalable and distributed object store for Hadoop. Moreover, applications utilizing frameworks, such as Apache Spark (an engine enabling large-scale data processing), Apache Hive (a software facilitating the management of large datasets being in distributed storage by using Structured Query Language (SQL)) and Apache YARN (briefly analyzed above), can operate natively without any alterations.