In the case of most wrappers it is possible to specify metadata of the
output schema (
OUTPUTSCHEMA) they provide, i.e. the fields that will
represent the data extracted from the source. These fields can be of
SIMPLE: fields belonging to basic data types such as text strings, integers, etc. Optionally, you can indicate if they can appear in query conditions of the wrapper. Query fields can be mandatory (every query must include a condition for such field) or optional. When specifying a simple field, its Java data type is also specified. For that, the conversion tables specified in the section Native-type Conversions of a Wrapper to Java Types must be taken into account.
REGISTER: formed by one or various fields, both simple and compound.
ARRAY: lists composed by register-type fields.
Furthermore, a series of restrictions can be indicated for each output schema field:
- Whether the field can include null values (
NULL) or cannot (
NOT NULL). The default value is
- Whether the results can be ordered by the (
SORTABLE) field or not (
NOT SORTABLE). It is also possible to specify that the results can be sorted by the field but only in ascending (
SORTABLE ASC) or descending (
SORTABLE DESC) order. The
SORTABLEvalue is assumed by default.
- Whether the field can be updated in an
UPDATEABLE) or cannot (
NOT UPDATEABLE). The
UPDATEABLEvalue is assumed by default.