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Komposition und Interoperabilität von IT-Systemen - Entwurf vom 9.1.2021

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In diesem Artikel diskutiere ich Interoperabilität von berechenbaren Systemen mithilfe des mathematischen Konzepts der Komposition. Die zentrale Vorstellung ist, dass Systeme durch Interaktion komponieren und diese Komposition mathematisch als Operator, also als Funktion auf Systemen beschreibbar ist. Daraus ergibt sich der Begriff des Interface eines Systems, als Zusammenfassung aller seiner auf die Komposition bezogenen Angaben, auf natürliche Art und Weise ebenso wie der Begriff der Komponente als eines Systems, das für eine bestimmte Komposition konstruiert wurde. Ich unterscheide zwei grundsätzlich verschiedene Kompositionen von Systemen. Zunächst die hierarchische Komposition, die Systeme als Ganzes erfasst und zur Bildung von Supersystemen führt. Sie basiert auf den Kompositionsregeln berechenbarer Funktionen und führt zu den Interfaces der Operationen (+Events) sowie zu Komponentenhierarchien. Demgegenüber steht eine zweite Form der Komposition, die Systeme nur partiell im Sinne einer Projektion erfasst und zu vergleichsweise loser Kopplung führt, mit dem Interface der Protokolle. Damit sind Interfaces, die Operationen repräsentieren, per Definitionem nur für hierarchische Kompositionen geeignet und keine wesentliche Hilfe in der Darstellung netzwerkartiger ''horizontaler'' Interaktionen. Um die Anwendbarkeit des Kompositionskonzepts zu demonstrieren, werden verschiedene System-, Interface- und Komponentenmodelle aus der Literatur diskutiert, u.a. das Komponentenmodell verteilter Objekte, sowie die Interfacekonzepte von SOA und REST.
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