What are the recommended guidelines for choosing between SubmodelElementList and SubmodelElementCollection when designing a submodel?

[SAidta]

SubmodelElementList

• When should a list structure be preferred?

• How should sorting and ordering be handled within a list?

• Are there best practices for defining constraints on the list elements?

SubmodelElementCollection

• When is a collection more appropriate than a list?

• Should collections always represent a group of related elements that do not require a strict order?

• Are there any performance or implementation considerations when using collections?

General Best Practices

• Are there specific IDTA guidelines or recommendations for when to use each structure?

• Any examples of good implementations in existing submodels?

[BirgitBoss]

See for explanation when to use SML: https://industrialdigitaltwin.io/aas-specifications/IDTA-01001/v3.1/spec-metamodel/submodel-elements.html#submodel-element-list-attributes

What makes it sometimes difficult whether SML or SMC are suitable are generic Submodel Templates just stating: make several SMC proprietary to your product or use case or algorithm etc. In these cases the SMC are not very similar w.r.t structure etc.. and only have a very high-level abstract common semantics. In case the semantics is "https://admin-shell.io/SMT/General/Arbitrary" then it is no SML.

[StenGruener]

SubmodelElementCollection should be considered as "data class" or "struct" equivalent in programming, while SubmodelElementList should be considered equivalent as a "list" construct.

• Use SubmodelElementList for lists of the same type (e.g., multiple temperature readings, multiple inspection results).
• Use SubmodelElementCollection for grouping related elements which are re-usable (e.g., metadata of a document, machine configuration settings) by having a dedicated semantic ID.

Additionally, SubmodelElementCollections do not have any warranty of the order of the items being fetched using APIs, while SubmodelElementLists do.

Older submodel templates (prior to v3 of the meta-model) used SubmodelElementCollections for both concerns which is indicated by idShorts in a format [idShort]_{00}, those should be migrated to lists,

Selection of the modeling tactics has an implication on querying -> #128

-> @MichaelHoffmeisterFesto how to include this guidance into the text of the SMT modeling guide?

[MichaelHoffmeisterFesto]

@StenGruener: This is a good proposition, I want to take this to the "How to write a SMT" document. In middle time frame, I will set up a next version of the document and will try to remember ;-) to include.

[StenGruener]

thanks, cool, i will keep it open so we can track :)

[StenGruener]

In case it is still a question, we need to formulate a response on the FAQ