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Figure 1. Sample Star Schema
THE DISTRIBUTED QOS-
ORIENTED WAREHOUSE
replica of the searched data, then the scheduler
looks for it at the grandparent node, and so on.
Whenever the number of searched nodes is greater
than a defined value, a new data replica is created.
Such newly created replica is placed at the node
that maximizes the number of queries that can be
answered without creating new replicas.
Maximizing the economic value of locally
stored data is the objective of the strategy proposed
by Haddad & Slimani (2007). In such strategy,
there is a price to access each data fragment.
Each node tries to foresee the future price of the
fragments and stores the ones that are forecasted
as the most valuable.
Most of the abovementioned strategies are
oriented for file-based grids. Others are related
to best-effort oriented scheduling in grid-enabled
databases. But all of them are somehow related
to the aspects we deal with in the next Sections.
In the next Section, we discuss the architecture
and scheduling for the QoS-oriented grid-based
distributed data warehouse.
Data warehouses are huge repositories of historical
data. They are subject-oriented: a certain subject
(revenue, for example) is analyzed considering
several distinct measures (e.g. time period). Each
analyses measure domain is called a
dimension
.
Therefore, the DW is a multidimensional space.
Such space is commonly represented in relational
databases as
star schemas
(Chaudhuri & Dayal,
1997), with several distinct
dimension tables
and
a huge
facts table
. The dimensions tables store
information about the analyze measures domains.
The facts table stores data that represents the
events of the real world and pointers to dimen-
sions tables. Figure 1 presents an example of a star
schema (in the remaining of this chapter, tables
are considered to be conceptually organized in a
star schema).
The Grid-based data warehouse is accessed
by users of geographically distributed sites which
may or may not belong to the same real orga-
nization, but that are put together within a grid
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