Such a version is used for analyzing the system performances and the optimization
of the data warehouse structure. The time dimension considered in this proposal
is the valid time, which is represented by means of two timestamps: the beginning
valid time and the ending valid time.
286 Combi & Oliboni
Copyright ?© 2007, Idea Group Inc. Copying or distributing in print or electronic forms without written permission of
Idea Group Inc. is prohibited.
Representing. Semistructured.Temporal.
Data.Warehouses
Data stored in a warehouse usually come from general heterogeneous data sources,
and are semistructured in nature, thus a general and flexible data model to represent
information stored in the data warehouse is needed. Moreover, data warehouses usually
are used as a repository for time varying information. This means that, temporal
aspects are a very important issue in this context.
In this section, we consider the main topics related to the management of time in
semistructured data warehouses. In particular, we describe how to represent a data
warehouse by means of a graph-based temporal semistructured data model, and
propose the set of constraints needed to manage in the correct way the considered
time dimension in the warehouse context.
In Figure 2 a GEM graph representing a portion of a data warehouse is reported.
In this example information about products in a catalogue are stored.
Pages:
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529