[DFDL-WG] proposal: add fn:error function and dfdl:hex function to DFDL

[Steve Hanson]

Adding fn:error means DFDL would have two mechanisms for issuing errors in 
asserts and discriminators - is that a problem?

Regards

Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848



From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     dfdl-wg at ogf.org, 
Date:   20/06/2013 18:19
Subject:        [DFDL-WG] proposal: add fn:error function and dfdl:hex 
function to     DFDL
Sent by:        dfdl-wg-bounces at ogf.org




Proposed: add fn:error function and add dfdl:hex function.

DFDL only needs one of the several variations of fn:error

fn:error($error as xs:QName?, $description as xs:string) as none

dfdl:hex($num as xs:integer) as string

The dfdl:hex function inverts the behavior of the dfdl:byte, and related 
functions (currently also proposed) which take a string specification of a 
hex value. The argument to dfdl:hex can be a long, unsignedLong, or any 
subtype thereof. The number of hex digits in the resulting string is a 
function of the input type. If byte or unsigned byte, exactly 2 hex digits 
are produced, for short and unsignedShort, 4 hex digits, and so on. The 
resulting value contains a prefix 'x' character as its first character. 
So:

dfdl:short(dfdl:hex(xs:short(208))) eq xs:short(208)

is true, and a corresponding tautology holds for all the other DFDL 
functions that construct integers from hexadecimal, if you replace the 208 
above with a value in range for the corresponding numeric type.

Example: 

This allows a meaningful error message that includes the offending parts 
of data. 

fn:error(ex:magic_number, fn:concat("The magic number: 0", dfdl:hex(.), " 
was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian)."))

The $error argument (of type QName) is used in an implementation-dependent 
manner to provide the context of the error. So for example, if namespace 
prefix 'ex' is bound to 'http://example.com' then the above call might 
produce:

"Error: {http://example.com}magic_number - The magic number: 0xFEFF0000 
was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian)."

Only the part of the above string after the hyphen is standardized. The 
hyphen and part before the hyphen is implementation dependent. 
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