The increasing pressure of the environment affecting modern organizations requires the search for increasingly sophisticated ways to enable their survival and development. One such solution is the creation of supply chains, which in the 1990s allowed companies to meet the challenges posed by the environment. Currently, in the first decade of the third millennium, supply chains no longer seem to be enough. In the spirit of the proven supply chain idea, they are beginning to increase the number of links covered by optimization. Just as it happened a few decades ago, when companies went beyond the framework of individual organizations to create a supply chain, there is now a clearer trend of expanding the scope of activities by individual supply chains and creating an organized group of supply chains, referred to in the literature as supply networks.
Logistics network as a basis for shaping supply chains
In general, a network can be understood as a collection of nodes connected by specific relationships. Despite a simple definition, the concept of a network can have many different interpretations. Thus, one can speak of railway networks, power lines connecting power plants, food networks, neural networks, semantic networks, and trade relationship networks. Scientific interest in networks has a long tradition. It is associated with the emergence of graph theory in mathematics and the appearance of social network analysis as a research area in sociology. The transfer of network theory to the field of logistics is associated with the desire of enterprises to develop procurement, production, and distribution, increase flexibility, and utilize synergistic effects of cooperation. As a result, organizations that are independent in terms of organization and law become participants in so-called logistics networks. To explain the concept of a logistics network, one can use one of the branches of mathematics – graph theory. A logistics network in a mathematical sense can therefore be defined as a directed graph G = (V, E) (where: V is a set of nodes, and E is a set of edges), in which each edge has a non-negative capacity c (u, v)≥ 03. A graphic image of a logistics network in terms of graph theory is shown in Figure 1.
A logistics network from the point of view of graph theory is a group of nodes connected by lines symbolizing mutual relationships of a logistical nature. Each directed edge in the network can be interpreted as a channel through which something flows. Each channel has a fixed capacity, and the vertices of the network are points where channels converge. Relationships in the network are therefore characterized by the tension between autonomy and interdependence, loyalty to the group and individuality, competitiveness and cooperation. In a logistics network, there is a multitude and diversity of material flows and related information, starting from the moment of obtaining raw materials to the delivery of products to the final recipient.
Therefore, a logistics network can be treated as a set of direct connections of a logistical (material-information) nature, which create interdependencies between companies and create a context for establishing connections that give individual companies functions and allocate resources for their implementation. This means that a logistics network is created by nodes (specific companies) between which there are certain connections of a logistical nature, which are the basis for creating structures much more organized than those that occur in the network itself. An example of an organization created based on a logistics network is a supply chain.
Shaping inter-organizational relationships in supply chains
The two-aspect way of considering the issues of the network and the supply chain constituting within it is the result of observing economic activity. In practice, the mere occurrence of material-information connections between specific entities does not mean that these relationships are optimal, i.e., properly planned, organized, and implemented. Comprehensive optimization of logistical connections occurring between a group of entities creates the organizational basis for shaping supply chains. Supply chains are formed as a result of the progressive process of eliminating barriers between companies and going beyond the traditionally shaped boundaries of enterprises. Supply chain links take on joint total responsibility for the product life cycle, starting from the sources of raw materials and materials, through their processing and assembly, and ending with the distribution and sale of final products (Figure 2).