Databases Reference
In-Depth Information
Figure 2.5:
Example of iconic representation (from
Tsuda et al.
,
1990
).
of the reality are first perceived, and then specific details may be viewed. The top-down strategy is
implemented in several ways. The first one can be seen as a sequence of iterative refinements, i.e.,
the system provides for each schema a library of top-down refinements. Each refinement can be
obtained from the previous one by means of transformations, which, when applied to atomic objects,
result in more detailed structures. A similar approach is implemented by providing either selective
or hierarchical zoom. The user can also graphically edit the schema, so that irrelevant objects can be
removed from the screen.
Another well established technique for learning about the information content of a schema
is
browsing
. Browsing is essentially a viewing technique aimed at gaining knowledge about the
database. In principle, it can handle both schemas and instances in a homogeneous way. Assuming
that the user has only minor knowledge about the database, she/he starts the interaction by examining
a concept and its neighborhood (adjacent concepts, i.e., concepts that are at distance one from the
selected concept, can be considered as a first level of explanation of the examined concept). Next, a
new element is selected by the user from adjacent concepts to be the current one, and its neighborhood
is also shown: this process proceeds iteratively.
An alternative approach to top-down refinement and browsing is
schema simplification
. The
idea here is to “bring the schema close to the query.” This is done by building a user view resulting
from aggregations and transformations of concepts of the original schema. While in the top-down
approach, it is possible to locate concepts that exactly match the initial schema (at different levels of
