EMLDataSource output as Ptolemy records
Currently, when an eml2 datasource is dragged to the graph display, a port
appears for each column in the datatable. Each port is given a name
corresponding to the column name in the data table. A sequence of tokens is then
output when the workflow runs, one for each row. The length of the sequence must
be set by 'hand' either in the Director or somewhere else.
In many cases, it would seem appropriate to not output a sequence of tokens, but
rather to include a single token which contains the column name, the number of
rows, and the individual cell data. In Ptolemy/Kepler this can be done with a
record token. The record name is the name of the column, the record contents is
an array which contains the contents of the cells. The array length is the
length of the column.
#1 Updated by Dan Higgins about 15 years ago
Upon consideration, there are two options that should be considered.
1) Show each column as a port, as is currently done in the default, but output a
single ARRAY from each port where the length of the array is the number of rows
in the column. Some arrays would be doubles, some integers, and some strings,
depending on the content of the column. The number of rows would be implicit in
the vector lenght. (call this "ColumnVector" output?)
2) Optionally, have a single record port where named column arrays are the items
in the record (ie col name is the name of record item, with all columns
included). This might be called a "Column-based Record" view and represents an
entire data table with a single record token.
#2 Updated by Shawn Bowers about 15 years ago
I don't think it is correct to have one port per attribute. This approach
looses the information that the ports are actually dependent. This assumes a
particular domain functionality (i.e., that the director knows the dependency);
but the constraint cannot be captured in Ptolemy's constraint language.
From a modeling perspective, it is more appropriate in Ptolemy to use a single
port that outputs a tuple (i.e., a record). Of course, one could always connect
an array deconstructor after the data set if desired. This approach (of
outputing tuples instead of individual values) follows more closely the standard
approach used in database systems and makes collection-oriented
dataflows/programming much easier.
#3 Updated by Jing Tao about 15 years ago
In EML2DataSource actor, two options - output as column vector or as column
based Record, were added. If user chose the first one - as column vector as
output, the output will be a ArrayToken which contains a array with entire
column data for this field. If user chose the second one - as column based
record, the port will output whole table as an array of columnDataArray.