## 2 Traceability  
### Literature Review of Traceability--Definitions and Categorizations  
Traceability, also known as the principle of \"one step back one step forward\", is the ability to recall all the information about the origin of a food product [2]. Another definition of traceability, given by the International Organization for Standardization (ISO) in ISO 22005:2007, is the \"ability to follow the movement of a feed or food through specified stage(s) of production, processing and distribution\" [3]. The European Union General Food Law EC 178/2002 defines traceability as the ability, in all production, processing and sales stages, of tracing and tracking the food [4]. An overview of the product and information flows in a typical traceability system is depicted in Figure 1.  
Considering all the above, food product traceability contains information about the food ingredients, the food sources, processing as well as transportation and storage conditions. An ideal agriculture traceability system would also contain information about each and every ingredient of the final product. Thus, to be considered effective, a traceability system must contain information, both quantitative and qualitive, about the final food product and its origin. According to [PERSON] et al., there are four major questions that need to be answered regarding the development of a traceability system [5]:  
1. Which data are important and must be collected?  
Figure 1: Traceability system product and information flow.  
2. Who is the owner of the information in every stage of the supply chain?
3. Which tools must be used for data collection (sensors, network, etc.)?
4. How should the data be managed in order to be available and understandable for both the stakeholders and consumers? [PERSON] et al. and [PERSON] et al. identify two different levels of traceability:  
1. The intra-company (internal) level;
2. The supply chain or external level.  
Specifically, the internal level traceability is carried out by a single actor (company, organization, etc.) and through internal procedures [5; 6]. Furthermore, intra-company traceability tries to identify the origin of the product's ingredients, packaging, etc., in case this actor of the supply chain is asked. On the other hand, the external traceability is a combination of intra-company processes and a reconstructing procedure of the whole history of the specific product [6]. Subsequently, all the stakeholders in a supply chain must be involved and coordinate with each other in order to produce a trustworthy outcome in terms of traceability.  
Another categorization regarding the traceability level has been performed by the European Community market, which distinguishes the mandatory traceability and the voluntary traceability [5; 7]. The mandatory traceability mainly has to do with financial purposes and lacks detailed information about the products regarding quality aspects. Supplementary to mandatory traceability, voluntary traceability refers to the ability of every actor on the supply chain to freely select what data to gather [5]. Justifying its name, voluntary traceability is not compulsory for stakeholders to implement. Trustworthy and complete traceability is only possible when both mandatory and voluntary traceability processes exist. Stakeholders involved in the supply chain enable a more detailed and qualitive traceability system when they voluntarily add information. A main challenge for voluntary systems lies in their complexity, since every actor may have their own standards and methods for tracking and tracing a product, leading to a wide variety of acquired data [8].