[jira] Assigned: (TUSCANY-2239) Support for mutually-exclusive intents

["Venkatakrishnan (JIRA)" <tu...@ws.apache.org>]

     [ https://issues.apache.org/jira/browse/TUSCANY-2239?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Venkatakrishnan reassigned TUSCANY-2239:
----------------------------------------

    Assignee: Venkatakrishnan

> Support for mutually-exclusive intents
> --------------------------------------
>
>                 Key: TUSCANY-2239
>                 URL: https://issues.apache.org/jira/browse/TUSCANY-2239
>             Project: Tuscany
>          Issue Type: New Feature
>          Components: Java SCA Core Runtime
>            Reporter: Greg Dritschler
>            Assignee: Venkatakrishnan
>         Attachments: tuscany-2239.patch
>
>
> The SCA Policy specification does not provide a means to define intents which are mutually exclusive.  This is a noticeable omission when considering the intents in the SCA Transaction specification which are mutually exclusive by nature (managedTransaction vs. noManagedTransaction, propagatesTransaction vs. suspendsTransaction).   There is a need to be able to define intents which are mutually exclusive and for the exclusion to be checked by the SCA runtime to avoid the error of specifying exclusive intents on a single artifact.  In addition, there should be rules defined for the handling of mutually exclusive intents which are attached at different levels of a composite or a hierarchy of composites.
> I have attached a patch to provide the capability to define mutually exclusive intents.  This is achieved using a new @excludes attribute on the <intent/> element in definitions.xml.  For example:
>     <intent name="propagatesTransaction" constrains="implementation" excludes="suspendsTransaction"/>
> @excludes is a list of intents which are mutually-exclusive with the named intent.  In order to be effective, a reciprocal definition needs to be made as shown below.
>       <intent name="suspendsTransaction" constrains="implementation" excludes="propagatesTransaction"/>
> The patch makes no assumptions about the relationship of qualified intents to the base intent.  Therefore exclusive relationships between qualified intents need to be spelled out.
>       <intent name="noManagedTransaction" constrains="implementation"
>         excludes="managedTransaction managedTransaction.global managedTransaction.local"/>
> A key part of the patch is that there now are two types of intent inheritance with respect to exclusive intents.  There is a "default" inheritance between certain hierarchical elements within a composite.  For example consider this snippet from a composite:
>     <component name="C1" requires="propagatesTransaction">
>         <reference name="r1"/>
>         <reference name="r2"/>
>         <reference name="r3" requires="suspendsTransaction"/>
>     </component>
> In this case the first two references inherit the default intent "propagatesTransaction" from the component element.  However the third reference does not inherit it because it specifies an exclusive intent "suspendsTransaction" which overrides the component-level default.
> The second type of inheritance is used when inheriting intents from an implementation (e.g. introspected Java code, or an implementation composite).  In this case the intents of the implementation cannot be overridden.  Consider this example:
>     <component name="D1">
>         <implementation.composite name="CZ1"/>
>         <reference name="r1" requires="suspendsTransaction"/>
>     </component>
> Let's assume CZ1 contains the component C1 shown earlier and that it promotes the component reference C1/r1 as r1.  C1/r1 has the intent "propagatesTransaction".  This intent is considered a requirement of the implementation and it cannot be overridden by the using composite.  Therefore D1 is in error.

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