scope:

Scope of version 1.0

The goals of version 1.0 are as follows:

1. Leverage XML technology and concepts

2. Support very efficient parsers/formatters

3. Avoid features that require unnecessary data copying

4. Support round-tripping, that is, read and write data in a described format from the same description

5. Keep simple cases simple

6. Simple descriptions should be "human readable" to the same degree that XSD is.

The general features of version 1.0 are as follows:

a) Text and binary data parsing and unparsing

b) Validate the data when parsing and unparsing using XSD validation.

c) Defaulted input and output for missing representations

d) Reference - use of the value of a previously read element in subsequent expressions

e) Choice - capability to select among format variations

f) Hidden groups of elements - A description of an intermediate representation the corresponding Infoset items of which are not exposed in the final Infoset.

g) Basic arithmetic in DFDL expressions.

h) Out-of-type value handling (e.g., The string value 'NIL' to indicate nil for an integer)

i) Speculative parsing to resolve uncertainty.

j) Very general parsing capability: Lookahead/Push-back

Version 1.0 of DFDL is a language capable of expressing a wide range of binary and text-based data formats.

DFDL can describe binary data as found in the data structures of COBOL, C, PL1, Fortran, etc., as well as standard binary data in formats like ISO8583 [ISO8583]. DFDL can describe repeating sub-arrays where the length of an array is stored in another location of the structure.

DFDL can describe a wide variety of textual data formats such as HL7, X12, CSV, and SWIFT MT [DFDLSchemas]. Textual data formats often use syntax delimiters, such as initiators, separators and terminators to delimit fields.

DFDL has certain composition properties. I.e., two formats can be nested or concatenated and the combination results in a working format.

The following topics have been deferred to future versions of the standard:

• Extensibility: There are real examples of proprietary data format description languages that were used as the base of experience from which standard DFDL was derived. However, there are no examples of extensible format description languages. Therefore, while extensibility is desirable in DFDL, there is not yet a base of experience with extensibility from which to derive a standard.

• Rich Layering: Some formats require data to be described in multiple passes. Combining these into one DFDL schema requires very rich layering functionality. In these layers one element's value becomes the representation of another element. DFDL V1.0 allows description of only a limited kind of layering.