List of variable names or Javascript expression that selects the variables of a table (ignored if value does not refere to a table). See javascript documentation: http://wiki.obiba.org/display/OPALDOC/Variable+Methods
missings
If TRUE, missing values will be pushed from Opal to R, default is FALSE. Ignored if value is an R expression.
identifiers
Name of the identifiers mapping to use when assigning entities to R (from Opal 2.0).
id.name
Name of the column that will contain the entity identifiers. If not specified, the identifiers
will be the data frame row names. When specified this column can be used to perform joins between data frames.
async
Whether the result of the call should be retrieved asynchronously. When TRUE (default) the calls are parallelized over
the connections, when the connection supports that feature, with an extra overhead of requests.