Information Technology Reference
In-Depth Information
Regarding incompleteness, there are very few works that tackle the problem [2].
Other works are somehow related to this issue, stressing the necessity for having facts
with at least one dimension value in every dimension in order to avoid complex and
misleading models [3]. Then, incomplete relationships between facts and dimensions
are not allowed, and certain real-world situations cannot be specified.
As presented in section 3, another problem relates to Grand Totals when it is ne-
cessary to group query results by individual members of the dimension table. This is
sometimes referred to as the grain of the dimension table. This problem can be
avoided by adding an allocation to the bridge table [4, 13]. The allocation factor indi-
cates what percentage of the associated fact should be credited to each group member.
Hence, the key to making allocations work lies in how the facts are accessed. Unfor-
tunately, allocation rules may not exist or the construction of allocation factors can be
bogged down in politics.
In [5, 7, 12], the authors present a classification of different kinds of complex dimen-
sion hierarchies, and they present a model for the conceptual design of complex multi-
dimensional models based on an extension of the well-known entity-relationships (ER)
model. The idea is to guide developers to properly capture at a conceptual level the
precise semantic of different kinds of hierarchies without being limited by current
OLAP tools.
3
The Proposed Method to Overcome Summarizability
Problems
3.1
Case Study: BASE Portal
In this section, we give a brief introduction of the BASE Portal (www.base.gov.pt), an
internet portal dedicated to public contracts gathering relevant information on public
procurement. The portal is the visible face of electronic public procurement and a
vital instrument for promoting transparency and accountability in Public Administra-
tion. It was designed to make participants aware of the need to apply the procurement
principles and rules in their communications, enabling citizens to search for informa-
tion related to contracts under framework agreements. The
Instituto da Construção e
do Imobiliário
(InCI), is the public entity responsible to manage the BASE portal.
The BASE Portal is used as a data source to present the DW developed in our case
study. The aim is to provide information related to the negotiation and execution
phases of all contracts signed under the Portuguese Public Contract Code (CCP).
Therefore the DW schema had to comply with public contract procedures and attend
data analysis requirements for citizens in general. The multidimensional schema also
had to be as simple as possible to be understandable and maintained by business-users
with no informatics expertise. The proposed technique is explained using a case study
approach describing the procedure that was implemented for representing non-
strictness by means of alternatives that broaden the use of bridge tables with a more
expressive solution. The main goal was to enable designers to abstract complexity at a
conceptual level without taking into account of more complex schema structures to
deal with non-strictness at different granularities.
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