Unit Cascade: Population as its own item

[BissonStatCan]

Population should modeled as its own distinct item in DDI 4.0, rather than being implicit or merged with others. This change would align DDI 4.0 with the Unit Cascade as described in the ISO proposal (Unit Type -> Universe -> Population), improve conceptual clarity, and strengthen interoperability and analytical precision.

Not having a population item makes it difficult to:

• Express time- and geography-bound populations unambiguously
• Reuse Universes across multiple Populations
• Align cleanly with the ISO proposal

[FlavioRizzolo]

I tend to agree. In addition to the reasons provided above, adopting the proposal would also align with the DDI-CDI model.

[wlthomas]

I agree in concept but 4.0 was intended to restructure 3.3 content with remodeling limited to serialization of content, remov al of XML centric structures like choice, and collapsing physical structure descriptions. This may be a 4.1 issue. Wendy L. Thomas ISRDI [retired] email: ***@***.***

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On Fri, Jan 30, 2026, 08:43 flavio ***@***.***> wrote: *FlavioRizzolo* left a comment (ddialliance/ddimodel#76) <#76 (comment)> I tend to agree. In addition to the reasons provided above, adopting the proposal would also align with the DDI-CDI model. — Reply to this email directly, view it on GitHub <#76 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAJT47MSQ6FCQQU2JQMVUOD4JNUZZAVCNFSM6AAAAACTOCZLZ2VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTQMRUGEZDEMJTGY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[DanSmith]

I think Population should be added to the 4.0 release, to closely align with ISO/PAS 25955, CDI, and the DDI Glossary.