Spatial Data Warehouses - Data Warehouse Systems: Design and Implementation - page 439

operations and that RangeValues could be easily constructed using
ST Value . With respect to the operations that allow the interaction
between domain and range, IsDefinedAt can be constructed using ST Value
and ST BandNoDataValue . Analogously, HasValue can be constructed
with ST Value ,and AtGeometry can be constructed with ST Value and
ST Intersection , for example. The other operations are not implemented at
all or cannot be easily implemented using the currently provided operations.
This is the case, for instance, of At , AtMin ,and AtMax , and the other
operations. The same occurs with the rate of change operations like the
partial derivatives. Although the built-in functions like ST Min4ma compute
aggregations in a neighborhood, they do not implement the functionality
required by the aggregation operations of Table 11.2 such as the FMin and
FMax operations.
11.4 Relational Representation of Spatial Data
Warehouses
In this section, we explain how a conceptual multidimensional schema is
translated into a relational schema in the presence of spatial data. As an
example, Fig. 11.15 shows the relational representation of the GeoNorthwind
conceptual schema given in Fig. 11.4 . In the figure, the spatial attributes are
written in boldface for better readability. We explain next this translation
based on the rules given in Sect. 5.3 .
11.4.1 Spatial Levels and Attributes
A level is mapped to the relational model using Rule 1 given in Sect. 5.3 .
However, since in the conceptual model the spatial support is repre-
sented implicitly (i.e., using pictograms), spatial levels require an additional
attribute for storing the geometry of their members. In addition, both
nonspatial and spatial levels may contain spatial attributes. Thus, we need
to generalize this rule to account for spatial levels and attributes as follows:
Rule 1S: A level L , provided it is not related to a fact with a one-to-
one relationship, is mapped to a table T L that contains all attributes
of the level. A surrogate key may be added to the table, otherwise the
identifier of the level will be the key of the table. For each spatial attribute,
an appropriate spatial data type must be chosen to store its geometry.
Further, if the level is spatial, an additional attribute of a spatial data type
is added to represent the geometry of its members. Note that additional
attributes will be added to this table when mapping relationships using
Rule 3S below.