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In the last few years multidimensional model-
ing has attracted the attention of several research-
ers that defined different solutions each focusing
on the set of information they considered strictly
relevant. Some of these solutions have no (Agrawal
et al., 1997; Pedersen & Jensen, 1999) or limited
(Cabibbo & Torlone, 1998) graphical support, and
are aimed at establishing a formal foundation for
representing cubes and hierarchies and an algebra
for querying them. On the other hand, we believe
that a distinguishing feature of conceptual models
is that of providing a graphical support to be eas-
ily understood by both designers and users when
discussing and validating requirements. So we
will classify “strict” conceptual models for DWs
according to the graphical formalism they rely
on, that could be either E/R, object-oriented or
ad hoc. Some claim that E/R extensions should
be adopted since:
Finally, we believe that ad hoc models com-
pensate for designers' lack of familiarity since:
1.
they achieve better notational economy;
2.
they give proper emphasis to the peculiarities
of the multidimensional model;
3.
they are more intuitive and readable by non-
expert users (Golfarelli, 2008; Hüsemann et
al., 2000; Tsois et al. 2001).
Remarkably, a comparison of the different
models made by Abello et al. (2006) pointed out
that, abstracting from their graphical form, the
core expressivity of most of the conceptual models
proposed in the literature is similar, thus proving
that the academic community has reached an
informal agreement on the required expressivity
(see Figure 1).
We emphasize that, within the DW field,
conceptual models and formal user-requirement
techniques are rarely discussed together to form a
comprehensive methodology. Furthermore, even
in these cases (Bonifati et al., 2001; Giorgini et
al., 2007; Guo, 2006; Mazon et al., 2007), non-
functional requirements are almost neglected or
they have been presented as a second class type
of requirement, frequently hidden inside notes.
On the other hand, the experiences in the broader
area of software engineering show that capturing
non-functional requirements without mapping
them into the conceptual model may determine
an information loss. In (Cysneiros & Sampaio do
Prado Leite, 2004) the authors show how to inte-
grate non-functional requirements into the Class,
Sequence, and Collaboration UML Diagrams.
The elicitation of non-functional requirements
at the conceptual level enables a traceability
mechanism. This mechanism provides a way of
representing in the models, which aspects are
there because of a non-functional requirement.
This has shown to be quite useful during the
model reviewing process. In different situations,
the reviewers were surprised by the inclusion of
elements in the conceptual models that did not
1.
E/R has been tested for years;
2.
designers are familiar with E/R;
3.
E/R has proved to be flexible and powerful
enough to adapt to a variety of application
domains
4.
several important research results were
obtained for the E/R model (Franconi &
Kamble, 2004; Sapia et al., 1999; Tryfona
et al., 1999).
On the other hand, advocates of object-oriented
models argue that:
1.
they are more expressive and better represent
static and dynamic properties of information
systems;
2.
they provide powerful mechanisms for ex-
pressing requirements and constraints;
3.
object-orientation is currently the dominant
trend in data modeling;
4.
UML, in particular, is a standard and is
naturally extensible (Luján-Mora, 2006;
Abello, 2006).
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