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https://issues.apache.org/jira/browse/ISIS-2553?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17294714#comment-17294714
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ASF subversion and git services commented on ISIS-2553:
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Commit 1acbf158558224b7f76a2ef18f09cf9db97d2e0a in isis's branch 
refs/heads/ISIS-2553_rational.id from Andi Huber
[ https://gitbox.apache.org/repos/asf?p=isis.git;h=1acbf15 ]

ISIS-2553: add ApplicationFeatureId to doc index

> Rationalize value types representing the metamodel, promote to applib if 
> possible.
> ----------------------------------------------------------------------------------
>
>                 Key: ISIS-2553
>                 URL: https://issues.apache.org/jira/browse/ISIS-2553
>             Project: Isis
>          Issue Type: Improvement
>            Reporter: Daniel Keir Haywood
>            Assignee: Andi Huber
>            Priority: Minor
>             Fix For: 2.0.0-M5
>
>
> We have some duplication between classes that describe elements of our 
> metamodel.  We also have a legacy of names that relate to physical aspects 
> (eg PACKAGE) whereas internally we are now using logical names (derived from 
> @DomainObject(objectType=), in other words ObjectSpecIdFacet) throughout.  
> And it would probably be safe to promote all of this to the applib once clean 
> - we currently only expose strings.
> Andi's summary of what we have:
>  # {{Identifier }}(AppLib): identifies an application feature, that is a type 
> (class) or a type's member (action, property or collection)
>  # TypeIdentifier  (AppLib): introduced this weekend, to effectively amend 
> the \{{Identifier }}with an additional field, that provides the logical name 
> of the type (aka *object-type*); immutable as much as possible, but allows 
> for lazy evaluation of the logical name, as it requires the meta-model to be 
> populated
>  # {{ObjectSpecId}}: (internal) class that wraps the logical name (String) of 
> the corresponding type (aka *object-type*)
>  # {{ApplicationFeatureId}}: (internal) Similar to Identifier, but splits the 
> logical type name or member name into its parts: PACKAGE, CLASS, MEMBER which 
> with logical name support now need to be interpreted as NAMESPACE, 
> LOGICAL-TYPE-SIMPLE-NAME and MEMBER, where the member part for actions also 
> includes its parameter list.
>  
> Further discussion:
>  * Dan - To me, it looks like TypeIdentifier and ObjectSpecId both describe a 
> type (aka ObjectSpecification)
>  * Andi - correct
>  * Dan -  Meanwhile Identifier is kind of a superclass that represents either 
> types or `ApplicationFeatureId`s
>   
>  * Dan - And we perhaps should rename from PACKAGE to NAMESPACE, etc, if 
> that's what these now are.
>  * Andi - Was my first thought today when I woke up, renaming those fields 
> within ApplicationFeatureId.
>   
> also note why the distinction between ObjectSpecId and TypeIdentifier: 
>  # ObjectSpecId: immutable, serializable
>  # TypeIdentifier: thread-safe lazy initialization, hence not serializable
> Further thoughts from Andi:
> TypeIdentifier lazily evaluates the logical name, because instances of 
> TypeIdentifier get created as early as the meta-model is in its phase of 
> being built up. So the logical name only gets evaluated and memoized when 
> first needed by any caller. So once memoized, the TypeIdentifier can be made 
> serializable easily. I might just do that, so we are on the safe side here.



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