Johannes Reich

Johannes Reich

Purpose: The purpose of this article is to propose, based on a model of an interaction semantics, a certain understanding of the ''meaning'' of the exchanged characters within an interaction. Methodology: Based on a model of system interaction, I structure the model of interaction semantics similar to the semantics of a formal language: first, I identify adequate variables in my interaction model to assign values to, and second, I identify the interpretation function to provide meaning. Thereby I arrive at a model of interaction semantics which, in the sense of the late Ludwig Wittgenstein, can do without a 'mental' mapping from characters to concepts. Findings: The key findings are a better understanding of the tight relation between the informatical approach to model interactions and game theory; of the central 'chicken and egg' problem, any natural language has to solve, namely that to interact sensibly, we have to understand each other and to acquire a common understanding, we have to interact with each other, which I call the 'simultaneous interaction and understanding (SIAU)' problem; why ontologies are less 'semantic' then their proponents suggest; and how 'semantic' interoperability is to be achieved. Value: The main value of the proposed model of interaction semantics is that it could be applied in many different disciplines and therefore could serve as a basis for scientists of natural sciences and humanities as well as engineers to understand each other more easily talking about semantics, especially with the advent of cyber-physical systems.

Johannes Reich, Tizian Schröder

In this article, we introduce a reference model for interaction semantics among communicating discrete systems to guide the discourse on interoperability. The necessary set of unifying concepts is small and comprises essentially the notion of discrete systems interacting by exchanging information. It is based on a simple, but nevertheless complete classification of system interactions with respect to information transport and processing. Information transport can only be uni- or bidirectional and information processing is subclassified along the binary dimensions of state, determinism and synchronicity. For interactions with bidirectional information flow we are able to define a criterion for a layered structure of systems: we name a bidirectional interaction "horizontal" if all interacting systems behave the same with respect to state, determinism and synchronicity and we name it "vertical" --- providing a semantic direction --- if there is a behavioral asymmetry between the interacting systems with respect to these properties. It is shown that horizontal interactions are essentially stateful, asynchronous and nondeterministic and are described by protocols. Vertical interactions are essentially top-down-usage, described by object models or operations, and bottom-up-observation, described by anonymous events. The reference model thereby helps us to understand the significant relationships that are created between interacting discrete systems by their interactions and guides us on how to talk about discrete system interoperability. To show its conceptual power, we apply the reference model to assess several other architectural models, communication technologies and so called software design or architectural styles like SOA and REST.

Johannes Reich

Several synergistic trends, subsumed under the phrase "Internet of things (IoT)" massively drive the increasing importance of networking applications. In the past, the exponential growth of the Internet was mainly due to semantically agnostic transport protocols. In the future it is to be expected that, because of the increasing autonomy of technical systems, it becomes necessary to better understand the nature of the semantics of these interaction networks to create appropriate networking applications. Appropriate means that the architecture of these applications allows to minimize the effort to adapt these applications to the permanently changing interaction networks. The proposed interaction oriented architecture is based on a reference model of interaction semantics. It provides guiding principles on how to design networking applications. The reference model of interaction semantics provides: a unifying description of the things in the physical, the information and the human world; an interaction model that is of direct runtime relevance; an understanding for how hierarchical structured components can cooperate loosely coupled; a concept to determine how much semantics has to be common to enable components of different semantic domains to cooperate loosely coupled; and a data type model. The software reference architecture provides: a definition of software layers; means to express vertical interactions, that is interactions which demarcate a software layer; means to express horizontal interactions, that is, between processes in the same software layer; a definition of a component and how to distinguish it from other entities like systems or objects; and a model how to separate reusable from non-reusable parts of an application's functionality.

Johannes Reich

This article develops a quality notion that is complementary to the system notion. As a major consequence, it becomes clear why quality can be measured only to a certain extend based on the issues of validity and incompleteness. First, there is an inherent conflict between the applicability and validity of quality measures and second, quality considerations almost always refer to high-dimensional spaces with only sparse knowledge also known as "curse of dimensionality". The resulting gap of knowledge has to be filled by experienced based heuristics. To deal with the curse of dimensionality, the heuristics of categorizing qualities into strategic and necessary is proposed. Strategic qualities provide contrast, while necessary qualities rather diminish contrast. In an economic context the presence of strategic qualities motivate a buy-decision and the absence of necessary qualities motivate a don't-buy-decision.

Johannes Reich

In this paper I elaborated on the idea of David Harel and Amir Pnueli to think systems and their interaction from the point of view of their compositional behaviour. The obvious idea to base the composition of systems on the concept of computable functions and their compositional behaviour leads to supersystem formation by composing simple and recursive systems. But this approach does not allow to account adequately for systems that interact with many other systems in a stateful and nondeterministic way, which is why I introduce the concept of interactivity and cooperation. In order to describe interactive systems satisfactorily, a balance is needed between the representation of their relationship to all the other systems and what happens within the systems. I thus introduce the complementary descriptions of external interactions and internal coordination, both based on a role concept in the sense of a projection of a system onto its interactions. It actually mirrors the internal vs. external distinction initially introduced by the system model and reflects the problem how systems are supposed to cooperate without melting into a common supersystem. Components become systems, intended for (a given) composition and with the notion of an interface we subsume all relevant information necessary for this composition. I introduce the concept of decisions as an additional internal input alphabet in order to determine nondeterministic interactions and thus fictitiously assume a system function where we actually do not have the knowledge to do so. Thus, the close relationship between protocols and games becomes obvious. Finally, I transfer the gained insights to the field of IT system architecture and introduce the concept of the "interaction oriented architecture (IOA)" for interactive systems with its three elements of roles, coordination rules, and decisions.