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" The Times They Are A-Changing " (B. Dylan), and with them the structures, schemas, master data, etc. of data warehouses. For the correct treatment of such changes in OLAP queries the orthogonal-ity assumption of star schemas has to be abandoned. We propose the COMET model which allows to represent not only changes of transaction data, as usual in data(More)
A data warehouse (DW) provides an information for analytical processing, decision making, and data mining tools. On the one hand, the structure and content of a data warehouse reflects a real world, i.e. data stored in a DW come from real production systems. On the other hand, a DW and its tools may be used for predicting trends and simulating a virtual(More)
In data warehouses measures are analyzed along different dimensions. Although the structures of these dimensions change over time, data warehouse tools currently in use are not able to deal with these modifications in a sophisticated way. In this paper we present a bi-temporal extension of the COMET metamodel. This extension enables us to represent not only(More)
Ontologies are shared conceptualizations of certain domains. Especially in legal and regulatory ontologies modifications like the passing of a new law, decisions by high courts, new insights by scholars, etc. have to be considered. Otherwise, we would not be able to identify which knowledge (which ontology) was valid at an arbitrary timepoint in the past.(More)
Data Warehouses provide sophisticated tools for analyzing complex data online, in particular by aggregating data along dimensions spanned by master data. Changes to these master data are a frequent threat to the correctness of OLAP results, in particular for multi-period data analysis, trend calculations, etc. As dimension data might change in underlying(More)
In a typical BI infrastructure, data, extracted from operational data sources, is transformed and cleansed, and subsequently loaded into a data warehouse where it can be queried for reporting purposes. ETL — the process of extraction, transformation, and loading, is a periodic process that may involve an elaborate and rather established software ecosystem.(More)
In this position paper, we will discuss the interoperability between different versions of a system (an ontology). In particular, we briefly present and analyze our approach to deal with changes in ontologies. Furthermore, we discuss two open questions in the area of temporal ontologies: a) The definition of Inter-Structure Ontologies to describe the(More)
A source for errors in results of OLAP queries lies in neglecting changes in dimension data of Data Warehouses over time. In addition to the correct representation of such changes in temporal data warehouses it is necessary to discover such changes when they appear in the sources of a data warehouse. We propose to use data mining techniques in form of(More)