Bill Hibbard wrote:
How are you going to pass the information about which table is numerical
and which is textual?
Someone could create a fairly general VisAD interface to
SQL by an implementation of the Form interface. The Open()
method signatures of Form take a file name and a URL name.
These are Strings and can be interpreted however the
For a basic SQL interface, the name would probably refer
to a single table, and would return a Field with MathType
of the form:
(record_index -> (domain1, domain2, ..., domain_last))
Where domain1, domain2, ..., domain_last are the numerical
and text domains in the table. If all the domains are
numerical, the Field can be a FlatField. Otherwise it
must be a FieldImpl. An SQL interface may offer the option
of excluding the text domains, in order to force a FlatField
(much more efficient than a FieldImpl).
For our app, we had
( x -> y) (FlatField, which represents a time series, i.e. a simple 2D plot)
whereas you're suggesting
( record_index -> (x,y))
which when mapped
x -> XAxis
y -> YAxis
is depicted as 2d scatter plot. (Am I right?)
So I'm still with my approach (though I might take back my "it is
impossible to write an adapter which will work with every JDBC-capable
database" without adding at least "which will give you the data
depiction you want" ;-)
The mapping to displays would be specified by a set of
ScalarMaps of domains to DisplayRealTypes.
If domains split into independent and dependent variables,
then the application would need to rearrange the MathType
to get something like:
((domain1, domain2) -> (domain3, ..., domainN))
with an appropriate domain Set. This is like what Donna has
done, constructing an Irregular2DSet.
A SQL interface could also return a database of multiple
tables as a Tuple of Fields, one per table.
Justin and Donna, if one of you or anyone creates such a
SQL interface, we would love to add it to VisAD, or add a
link to the VisAD web page. Note for any Form method
signatures you don't want to implement, just have them
throw a visad.UnimplementedException.
Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI 53706
hibbard@xxxxxxxxxxxxxxxxx 608-263-4427 fax: 608-263-6738