Data Format Description Language (DFDL) v1.0 Specification
OGF Proposed Recommendation GFD-P-R.174, January 31, 2011


2.2 Schema Definition Error

When the DFDL schema itself contains an error, it implies that the DFDL processor cannot process data because the DFDL schema is not meaningful. It may be ambiguous, or contain conflicting definitions. Equivalently, we can say that there is no possible data that conforms to the schema; hence, the schema cannot be meaningful. All conforming DFDL processors must detect all schema definition errors, and must issue some kind of appropriate diagnostic message. The behavior of a DFDL processor after a schema definition error is detected is out of scope for this specification.

When a Schema definition error can be detected given only the schema, it is desirable, though not required by the DFDL standard, that such errors be detected and diagnostic messages issued before any data are processed. Of course not all schema definition errors can be detected without reference to data as some representation properties may obtain their values from the data (see section ‎2.3.1 Ambiguity of Data Formats).

The expression language included within DFDL is strongly, statically type checkable. This means that type checking of expressions can be performed without processing data, and implementations are encouraged to perform this checking statically so that schema definition errors having to do with type inconsistencies can be detected before processing data.

Note that schema definition errors cannot be suppressed by points of uncertainty.


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