Database Reference
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Fig. 1.
Constructs in source-model independent supermodel and model specific models
as well as the correspondences between them
and XSD, respectively) and the source-model independent supermodel, which
uses a small set of model-generic constructs, so called
metaconstructs
[1] to rep-
resent model-specific constructs by aggregating over their similarities (see the
UML diagram in the top half of Figure 1). Model management operators are
defined over the constructs in the supermodel, which is depicted by the arrow
in the top right corner of Figure 1. The UML diagrams in Figure 1 also include
additional constructs that are required to represent all the information present
in the models, e.g.,
ComponentOfForeignKey
and
Nest
. By capturing both, the
model-specific constructs and the model-generic representations of a schema,
this approach is both model-independent and model-aware. Table 1 lists the
model-generic metaconstructs and their corresponding model-specific constructs
for relational and for XSD models. The dashed lines in Figure 1 from the model
specific constructs to the model generic metaconstructs depict the correspond-
ing constructs in the different models. The correspondences between the model
specific and the model generic constructs are utilised during import of models,
information that we later utilise in the opposite direction for query translation
(depicted in Figure 1 by the dashed lines from the model generic constructs to
the model specific constructs). As this paper focusses on relational and XSD
models only, the remaining models that can be represented by the universal
model have been omitted here, but are described in [4].
3 Query Language
This section introduces the query language
SMql
, a declarative query language
inspired by SQL but defined over the constructs of the supermodel. A
SMql
query is of the form
SELECT
l
1
, ..., l
n
FROM
c
1
, ..., c
m
WHERE
p
,where
l
1
, ..., l
n
is a
project list of Lexicals,
c
1
, ..., c
m
∈{Abstract|Aggregation|StructOfAttributes}
