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Nowadays, smart systems require the use of Digital Twins (DTs) for their engineering and management. Self-updating capability is a key feature in the DT technology. This raises the challenge of model inference from data collected on the system and requires a formal framework be defined, in which a system representation can be coupled with inference methods to achieve automatic model updating. While data-based process model inference is a well-known technique, the inference of a simulation model from existing knowledge and collected data is yet an unexplored area. In this paper, we first clarify and explicitly define some key elements of the terminology related to the DT concept, including model update and model inference, and we propose a framework of inference capabilities based on a formal DT specification, which formally captures the conditions for different updating capabilities and relates them. That way, on one hand, the framework enables the use of symbolic approaches to build a DT with the desired inference capability, and on the other hand, it establishes a partial order relation between inference capabilities. Through a case study, we show how the framework helps formally specifying the DT model of a mobility system toward realizing a fully capable DT. [ABSTRACT FROM AUTHOR]

Hierarchical part-of relationships/aggregation structures and related queries are essential parts of information systems. However, relational database query languages do not explicitly support hierarchical relationships and queries. A hierarchical query may require a great number of join operations, which increases the effort in query formulation. Therefore, we propose path expressions in formulating hierarchical views over relational data because path expressions are a conventional and compact way to represent hierarchical relationships. We embed path expressions within SQL queries and compile them to standard SQL. This ensures that the path expressions can straightforwardly be implemented on the top of standard relational database systems. The compilation of a path expression is given by an attribute grammar, a conventional formalism to define the semantics of a language. [ABSTRACT FROM PUBLISHER]

Dataspace systems have been proposed recently as an alternative to the traditional data integration approach. They offer reduced setup time and costs by allowing cooperation among the data sources based on the knowledge gained gradually through user interaction. A dataspace is a collection of heterogeneous and beforehand unfamiliar but interrelated data sources. In this article, we consider dataspaces composed of XML-based data sources. The XML query and analysis systems designed to satisfy the user’s sophisticated information needs presuppose that they are familiar with the contents, structures and semantics of the underlying data sources. In order to provide this information, we introduce and specify a schemaless XML dataspace profiling system that assists the user in selecting data sources relevant to him/her and in validating their consistency by detecting the potential data conflicts among them. We also demonstrate how our approach affords the possibility of utilizing an advanced XML query system. [ABSTRACT FROM PUBLISHER]