A conceptual model for temporal data warehouses and its transformation to the ER and the object-relational models

摘要

The MultiDim model is a conceptual multidimensional model for data warehouse and OLAP applications. These applications require the presence of a time dimension to track changes in measure values. However, the time dimension cannot be used to represent changes in other dimensions. In this paper we introduce a temporal extension of the MultiDim model. This extension is based on research realized in temporal databases. We allow different temporality types: valid time, transaction time, and lifespan, which are obtained from source systems, and loading time, which is generated in the data warehouse. Our model provides temporal support for levels, attributes, hierarchies, and measures. For hierarchies we discuss different cases depending on whether the changes in levels or in the relationships between them must be kept. For measures, we give different scenarios that show the usefulness of the different temporality types. Further, since measures can be aggregated before being inserted into data warehouses, we discuss the issues related to different time granularities between source systems and data warehouses. We finish the paper presenting a transformation of the MultiDim model into the entity-relationship and the object-relational models.