# Graphs and social systems

A social system can be viewed as the set of relationships existing between entities such as individuals, groups, and institutions and forming a structured, coherent whole. Social system analysis is an inherently interdisciplinary academic field, which emerged from social psychology, sociology, statistics, graph theory, and other domains. For the last few decades, and in parallel with the development of the network science field, graph-based approaches dedicated to this purpose have gained a significant following in social sciences and humanities, and there are now tools commonly available for end-users. Thanks to the very generic nature of graphs, it is possible to take a method designed to handle a specific system, and apply it in a completely different context. For instance, a method allowing to detect functionally important proteins in a biological network can be used to identify key-players in a social network. However, due to lexical, methodological and cultural differences, being aware of the methods developed in other fields can be truly challenging for a researcher. The goal of this special issue is to try to bridge this gap, by exposing researchers to different tools and usages of the concept of graph, coming from out of their field. The general idea is to describe graph analysis methods and/or their application to specific social systems. We are interested in works proposing new analysis or extraction methods, likely to be used in various very different applicative contexts. We are also interested in works describing how an existing method, initially developed for a given context, was adapted and/or applied to graphs representing completely different systems. Finally, we are interested as well in works dealing with systems whose unique properties require the design of domain-specific methods.

### 1. Introduction to the special issue on Graphs & Social Systems

The principle of the Journal of Interdisciplinary Methodologies and Issues in Science (JIMIS) is that each issue is a special one, dedicated to a specific topic and handled by guest editors. This issue (the second of the journal) focuses on the use of graphs (and associated analysis tools) to model and study social systems. The guest editors for this issue are Rosa Figueiredo and Vincent Labatut.
Section: Issues

### 2. Reflections on Studying Signed Networks

Despite considerable success, the balance theoretic approach to studying signed relations has encountered some serious problems, both substantive and methodological. The more consequential of them are outlined along with reasons for why solving them is critical. In essence, an agenda of research problems is laid out with many juicy problems to solve. These reflections, while setting a context in prior work, are far more concerned about looking to the future and identifying problems whose solutions hold the potential for transforming the field.
Section: Issues

### 3. Analyse des Préférences et Tournois Pondérés

Dans de nombreuses etudes expérimentales , on dispose de n ´ eléments ordonnés suivant plusieurs classements (votes, notes ou crit eres). Nous traitons et comparons deuxprobì emes : (i) Etablir un classement unique (ordre total) des n items et (ii) sélectionner les k meilleurs eléments parmi n. Il s'agit, dans les deux cas, de minimiser le nombre de préférences qui vont a l'encontre de ces 5 choix.
Section: Issues

### 4. Brazilian Congress structural balance analysis

In this work, we study the behavior of Brazilian politicians and political parties with the help of clustering algorithms for signed social networks. For this purpose, we extract and analyze a collection of signed networks representing voting sessions of the lower house of Brazilian National Congress. We process all available voting data for the period between 2011 and 2016, by considering voting similarities between members of the Congress to define weighted signed links. The solutions obtained by solving Correlation Clustering (CC) problems are the basis for investigating deputies voting networks as well as questions about loyalty, leadership, coalitions, political crisis and polarization.
Section: Issues

### 5. The Problem of Action at a Distance in Networks and the Emergence of Preferential Attachment from Triadic Closure

In this paper, we characterise the notion of preferential attachment in networks as action at a distance, and argue that it can only be an emergent phenomenon – the actual mechanism by which networks grow always being the closing of triangles. After a review of the concepts of triangle closing and preferential attachment, we present our argument, as well as a simplified model in which preferential attachment can be derived mathematically from triangle closing. Additionally, we perform experiments on synthetic graphs to demonstrate the emergence of preferential attachment in graph growth models based only on triangle closing.
Section: Issues

### 6. Analyse de réseaux criminels de traite des êtres humains: méthodologie, modélisation et visualisation

Cet article dessine le contexte d'une étude portant sur les réseaux criminels de traite des êtres humains et décrit la rencontre de trois champs disciplinaires engagés dans ces travaux: Droit, Sociologie et Informatique, ainsi que les éléments méthodologiques développés. Il pose les fondations d'une méthodologie venant en appui à l'étude juridique des réseaux criminels, et plus spécifiquement de ceux se livrant à des faits de traite des êtres humains. La science des réseaux'' (Network Science), vue à la fois comme une abstraction mathématique et une approche et méthodologie sociologique, sert de socle pour formuler et explorer un faisceau d'hypothèses éclairant le(s) mode(s) opératoire(s) des réseaux criminels. Les leçons apprises, nourries des interactions entre disciplines, permettent de dessiner les axes de travaux futurs pour améliorer la méthodologie avancée.
Section: Issues