Introduction

      Establishment of the Roadmap

      I.1. Preamble

      The use of the term “trace” is associated with many old and ancient practices - (traces of passage, heritage traces, etc.), but also with more specifically current contexts, such as that of the digital society. The question of the origin of a trace has always been of a particular interest to certain professionals: the investigator in pursuit of a criminal, the doctor researching symptoms, the archaeologist wishing to reconstruct the lifestyles of ancient civilizations, historians seeking to retrace the path of humans over the centuries, astrophysicists watching for gravitational waves, the tax inspector, etc.

      NOTE.– The concept of trace questions every period in the history of humanity and the cosmos, both past and future. The force of the questions on the nature of the concept of trace and its consequences is accentuated when scientific developments open up new horizons and when humans become aware that their present choices produce conséquences-traces¹ in their lives and in those of future generations.

      Today, more and more social actors in society (individuals, organizations, public institutions) are taking the concept of conséquences-traces into account in their activities, particularly as the digital society opens up other forms of presence in the world.

I.2. The call of digital society for new forms of traceability

      The pressing obligation to exist on the Web leads to the temptation to circulate pieces of information that are constantly renewed and multiplied, although quickly or poorly verified, in response to flattering misrepresentations (Goffman 1973) that invite the adoption of digital devices providing false appearances (Debord 1967). The machine records important digital inscriptions and circulates them according to a given algorithm logic.

      Initially, an algorithm is a logical sequence of actions. For example, a kitchen recipe is an algorithm that provides instructions to someone wishing to cook, by specifying the execution of tasks, and their contents, in a precise order. Based on such “recipes”, the first programmers designed computer algorithms whereby a digital algorithm provided pieces of information in the form of machine language. The algorithm ensures that these pieces of information followed a precise path resulting from binary answers (“yes” or “no”) to human-designed questions. The process enables the algorithm to produce a rationally constructed result.

      DEFINITION.– A digital algorithm is a numerical written form, of human reasoning (and thus a cognitive trace2) that is then integrated into a machine.

      We shall see further on³ that these algorithms, by working from numerical inscriptions – combining 0s and 1s – can cut the numerical sequences for other assemblies and other computations⁴ than those initially planned. The more numerous these manipulations, the more difficult it is to go back to the original inscriptions. This raises serious questions about the nature and validity of the results obtained from this process.

This is why the possibility of performing the path backwards, the so-called “tracing of computer processes” is of considerable importance in order to grasp the “relevance” (Sperber et al. 1986) of the data resulting from these successive transformations. Computer traceability is the possibility of identifying all the selection actions that lead to the retention of certain data and the exclusion of others. In some cases, this system can lead to the programmer, who designed the algorithm, being called into question⁵.

      Digital data processing produces what contemporaries call digital traces. They constitute a major challenge for all users of digital technology given that soon, the entire population of societies will have access to it⁶. For them, the reign of the “Internet of Everything” is now well established. Individuals and machines are permanently connected to each other, creating a continuous flow of meshed connections of interactions between networks that produce “trace-domino effects”⁷.

I.3. Enthusiasm for the place of the trace in crime series

It is by noting the current success of crime series and the place given to the examination of all objects, especially in relation to investigations that “make the traces speak” that has led us to choose this area to illustrate some⁸ of our explanations, even if this reference to investigations that seek to grasp the concept of trace is not original per se. In his analysis of the difference between indices (clue, index)⁹ and traces, Carlo Ginzburg (1989)¹⁰ gave the example of the sleuth Sherlock Holmes, whose ability to spot the smallest traces left by a culprit has remained famous in the history of literature.

      This reference to investigations is all the more relevant today, what with the generalized digitization of society, new forms of surveillance being introduced, possibilities of controlling what is said or done in communication situations, the breaking down of barriers between the public and private spheres, and direct or indirect dependency on decisions taken, on the basis of work carried out on computerized sorting systems¹¹ by using algorithms that transform them into data¹². Hence, the importance of questioning the concept of conséquence-trace¹³ in this development.

I.4. The investigation, an approach also used in the social sciences

Many