The stacking of membrane electrode assemblies (MEA) and bipolar plates is a key process in fuel cell stack production, in which requirements for high accuracy and shortest possible process time must be taken into account. In this paper technical systems for fuel cell stack assembly are analysed regarding means for handling, gripping and alignment of the components. The different methods are compared and evaluated, followed by a novel system allowing for an on-the-fly measurement of the position / Das Stapeln von Membran-Elektroden-Einheiten (MEA) und Bipolarplatten ist ein Schlüsselprozess in der Brennstoffzellen-Stack-Produktion, bei dem die Anforderungen an eine hohe Genauigkeit und eine möglichst kurze Prozesszeit berücksichtigt werden müssen. In diesem Beitrag werden technische Systeme für die Montage von Brennstoffzellenstapeln hinsichtlich der Handhabung, des Greifens und der Ausrichtung der Komponenten analysiert. Die verschiedenen Methoden werden verglichen und bewertet, gefolgt von einem neuartigen System, das eine on-the-fly Messung der Position ermöglicht.

Automatic summary tables (ASTs), more commonly known as materialized views, are widely used to enhance query performance, particularly for aggregate queries. Such queries access a huge number of rows to retrieve aggregated summary data while performing multiple joins in the context of a typical data warehouse star schema. To keep ASTs consistent with their underlying base data, the ASTs are either immediately synchronized or fully recomputed. This paper proposes an optimization strategy for simultaneously refreshing multiple ASTs, thus avoiding multiple scans of a large fact table (one pass for AST computation). A query stacking strategy detects common sub-expressions using the available query matching technology of DB2. Since exact common sub-expressions are rare, the novel query sharing approach systematically generates common subexpressions for a given set of 'related' queries, considering different predicates, grouping expressions, and sets of base tables. The theoretical framework, a prototype implementation of both strategies in the IBM DB2 UDB/UWO database system, and performance evaluations based on the TPC/R data schema are presented in this paper.