Type Conditionally Required 2C doesn't mean Empty if Unknown

[i3earci]

Bug description
Laterality Attribute shows wrong information

Steps for reproduction
Type Conditionally Required, Empty if Unknown (2C)

Expected behavior
Type Conditionally Required, Absent if Unknown (2C)

Additional context (e.g. screenshots)
https://dicom.nema.org/medical/dicom/current/output/pdf/part05.pdf
7.4.4 Type 2C Conditional Data Elements
...
When the specified conditions are not met, Type 2C Data Elements shall not be included in the Data Set unless it is specified that​
they may be present otherwise.

[MichaelLeeHobbs]

Response to #129 — Type 2C and "Empty if Unknown"

Verdict: not a bug — the label is correct, but it describes a different case than the one quoted in the report.

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There are two separate rules for a Type 2C element, and the label refers to the first one:

1. When the condition IS met → the element follows Type 2 rules, so it must be present and may be sent empty if the value is unknown. This is what "Empty if Unknown" describes.
2. When the condition is NOT met → the element shall not be included. This is the sentence quoted in the report.

Proof

PS3.5 Section 7.4.4 (Type 2C Conditional Data Elements):

"IODs and SOP Classes define Type 2C Data Elements that have the same requirements as Type 2 Data Elements under certain specified conditions. It is a protocol violation if the specified conditions are met and the Data Element is not included. When the specified conditions are not met, Type 2C Data Elements shall not be included in the Data Set unless it is specified that they may be present otherwise."

And PS3.5 Section 7.4.3 (Type 2), which 7.4.4 inherits from:

"However, it is permissible that if a Value for a Type 2 Data Element is unknown it can be encoded with zero Value Length and no Value."

So "Empty if Unknown" is the correct Type 2 semantic that 2C inherits. "Absent if Unknown" would not be right either — absence is driven by the condition not being met, not by the value being unknown.

Recommendation

Close as working as intended.

Note also that this repository stores only the bare type "2C" — the prose label is authored in the website, and the terminology it uses is the standard's own. Neither is this project's to change.

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Drive-by triage from a non-maintainer; the checks above are reproducible against the current standard and the JSON on master.