[jboss-jira] [JBoss JIRA] (DROOLS-1543) DMN ItemDefinition dependencies ordering

[Matteo Mortari (JIRA)]

    [ https://issues.jboss.org/browse/DROOLS-1543?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13400597#comment-13400597 ] 

Matteo Mortari commented on DROOLS-1543:
----------------------------------------

Additionally, furhter modifying such described Comparator in the only case of independency, to further order alphabetically by name, would introduce potential inconsistencies across the total ordering.

Assume the following:

{code:java}
Z
B
A -> Z
{code}

where B is independent from A, Z; and A depends on Z hence by definition A > Z.

{code:java}
A > Z // by definition as A depends on Z.

B < Z // comparing b with z, because they are independent, order them by name
A < B // comparing a with b because they are independent, order them by name
{code}

At this point the inconsistency is revealed over the total ordering because:

{code:java}
A < B < Z // descends from the last 2 comparison
inconsistent with:
A > Z // was the original by definition
{code}


> DMN ItemDefinition dependencies ordering
> ----------------------------------------
>
>                 Key: DROOLS-1543
>                 URL: https://issues.jboss.org/browse/DROOLS-1543
>             Project: Drools
>          Issue Type: Bug
>            Reporter: Matteo Mortari
>            Assignee: Matteo Mortari
>
> Using Java-api Comparator is not easily suitable to address the problem of ordering the ItemDefinition by their dependencies.
> If the Comparator is used to check purely for dependencies, returning 0 for indipendent elements, assume the following:
> {code:java}
> X
> Y -> Z
> {code}
> where X is independent from Y, Z; and Y depends on Z.
> {code:java}
> compare(X, Y) == 0 // by definition above
> compare(X, Z) == 0 // still, by definition above, X is independent also from Z
> compare(Y, Z) == 1 // because Y depends on Z, Y is bigger than Z.
> {code}
> The above breaks the API contract in the Java-API Comparator where stating:
> {quote}Finally, the implementor must ensure that compare(x, y)==0 implies that sgn(compare(x, z))==sgn(compare(y, z)) for all z.{quote}



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