Schema versioning in data warehouses: Enabling cross-version querying via schema augmentation

Abstract

As several mature implementations of data warehousing systems are fully operational, a crucial role in preserving their up-to-dateness is played by the ability to manage the changes that the data warehouse (DW) schema undergoes over time in response to evolving business requirements. In this paper we propose an approach to schema versioning in DWs, where the designer may decide to undertake some actions on old data aimed at increasing the flexibility in formulating cross-version queries, i.e., queries spanning multiple schema versions. First, we introduce a representation of DW schemata as graphs of simple functional dependencies, and discuss its properties. Then, after defining an algebra of schema graph modification operations aimed at creating new schema versions, we discuss how augmented schemata can be introduced to increase flexibility in cross-version querying. Next, we show how a history of versions for DW schemata is managed and discuss the relationship between the temporal horizon spanned by a query and the schema on which it can consistently be formulated.

A Review:Implementation Of OLAP Semantic Web Technologies For Business Analytic System Developement

“…Most of the existing work for bringing together OLAP and SW technologies focus on the scheme design issues, but our analysis work still unresolved The common characteristics of existing approach is that these can be deal with unstructured data only .To solve this problems we are going to use OLAP technology [9] .…”

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“…Being a "non-volatile collection of data" [46], the evolution changes of the target DW schema are typically represented in terms of different versions of a DW (i.e., multiversion DW). In particular, the most important issue was providing a transparent querying mechanisms over different versions of DW schemata (i.e., cross-version querying; [67,37]). For instance, a solution proposed in [37] suggested keeping track of change actions to further enable answering the queries spanning the validity of different DW versions.…”

“…In particular, the most important issue was providing a transparent querying mechanisms over different versions of DW schemata (i.e., cross-version querying; [67,37]). For instance, a solution proposed in [37] suggested keeping track of change actions to further enable answering the queries spanning the validity of different DW versions. These approaches provide a certain (Medium) level of malleability for data-intensive flows, but still lack the full automation of the evolution changes or applicability in the case of unpredictable complexity of data transformations.…”

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“…For example, Golfarelli (2006) suggests a formalization of the data warehouse, its changes and versioning strategy. An intersection operator is proposed to specify the effect of the changes on the data warehouse and to state the validity of current OLAP queries among different data warehouse versions.…”