[jira] [Updated] (SCXML-196) Redefine SCXMLSemantics to align with the Algorithm for SCXML Interpretation as described in the SCXML specification

["Ate Douma (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SCXML-196?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ate Douma updated SCXML-196:
----------------------------

    Description: 
One of the targets for the Commons SCXM 2.0 roadmap milestone 1 is to redefine SCXMLSemantics to align with the SCXML Algorithm for SCXML Interpretation, see: http://www.w3.org/TR/scxml/#AlgorithmforSCXMLInterpretation
The current SCXMLSemantics interface and its implementation is so much different from the algorithm in the specification that 'molding' it into what the algorithm now expects is too cumbersome.

The current SCXMLSemantics and its implementation will therefore be completely replaced with a new one, closely corresponding to the semantics of the SCXML Algorithm in the specification.

The algorithm described in the specification leaves plenty of room for optimization and choice of techniques.
For a first cut implementation though I intend to simply follow the described algorithm as close as possible, also to make sure not to deviate from the specification already too early :)
After the new implementation has been tested and validated to be conforming the expected behavior, or even later than that, the implementation surely can be refined and optimized further.

The changes needed for this task are closely related to those described in SCXML-197: Better separation of concern between SCXMLExecutor and SCInstance and introducing a new SCXMLExecutionContext.
Although through SCXML-197 already many improvements are realized, to be able to implement the new SCXMLSemantics requires additional (major) changes, which functionally should be regarded part of SCXML-197, but cannot be committed separately as the changes are too closely related.
I'll therefore update SCXML-197 describing those functional changes regarding the better separation of concerns, although they will be committed against this issue.

An important note is that with the re-implementation of the SCXMLSemantics, the static SCXMLHelper class, as well as the (Transition) Path helper class functionalities will be completely 'absorbed' into the model and the new algorithm implementation. These classes therefore no longer are used and needed and will be removed. 
Furthermore, the Step class now only is used from within the SCXMLSemantics implementation and therefore moved to the semantics package.

With these changes in SCXML-196 and SCXML-197, the goals for Milestone 1 on the roadmap to SCXML 2.0 have been completely met and I'll create a milestone 1 svn tag for it shortly. 


  was:
One of the targets for the Commons SCXM 2.0 roadmap milestone 1 is to redefine SCXMLSemantics to align with the SCXML Algorithm for SCXML Interpretation, see: http://www.w3.org/TR/scxml/#AlgorithmforSCXMLInterpretation
The current SCXMLSemantics interface and its implementation is so much different from the algorithm in the specification that 'molding' it into what the algorithm now expects is too cumbersome.

The high-level plan I have is to:
- fork SCXMLSemanticsImpl to SCXMLSemanticsImpl2, without implementing SCXMLSemantics
- fork SCXMLExecutor to SCXMLExecutor2, extending SCXMLExecutor
- switch to use SCXMLSemanticsImpl2 explicitly in SCXMLExecutor2
- start with simply implementing the SCXML Algorithm from 'scratch' in SCXMLSemanticsImpl2 using (top level) methods matching those described in the algorithm and refactor SCXMLExecutor2 to leverage this

With the above initial steps, the existing implementation will stay in place and remains available to compare and test the new implementation against.
There probably will be need to make accommodating changes in other areas, which I will try to keep compatible with the existing implementation or at least not to break it.
The reason to fork and extend SCXMLExecutor is that it is referenced and used in many other places (that is: currently), like in SCInstance. By extending it, the SCXMLExecutor2 can still play that role without directly breaking everything.

The algorithm described in the specification leaves plenty of room for optimization and choice of techniques.
For a first cut implementation though I intend to simply follow the described algorithm as close as possible, also to make sure not to deviate from the specification already too early :)
After the new implementation has been tested and validated to be comforming the expected behavior, or even later than that, the implementation surely can be refined and optimized further.
That also will be time to decide to drop and replace the existing SCXMLExecutor and SCXMLSemantics (both interface and implementation) with the new versions.



> Redefine SCXMLSemantics to align with the Algorithm for SCXML Interpretation as described in the SCXML specification
> --------------------------------------------------------------------------------------------------------------------
>
>                 Key: SCXML-196
>                 URL: https://issues.apache.org/jira/browse/SCXML-196
>             Project: Commons SCXML
>          Issue Type: New Feature
>    Affects Versions: 2.0
>            Reporter: Ate Douma
>            Assignee: Ate Douma
>             Fix For: 2.0
>
>
> One of the targets for the Commons SCXM 2.0 roadmap milestone 1 is to redefine SCXMLSemantics to align with the SCXML Algorithm for SCXML Interpretation, see: http://www.w3.org/TR/scxml/#AlgorithmforSCXMLInterpretation
> The current SCXMLSemantics interface and its implementation is so much different from the algorithm in the specification that 'molding' it into what the algorithm now expects is too cumbersome.
> The current SCXMLSemantics and its implementation will therefore be completely replaced with a new one, closely corresponding to the semantics of the SCXML Algorithm in the specification.
> The algorithm described in the specification leaves plenty of room for optimization and choice of techniques.
> For a first cut implementation though I intend to simply follow the described algorithm as close as possible, also to make sure not to deviate from the specification already too early :)
> After the new implementation has been tested and validated to be conforming the expected behavior, or even later than that, the implementation surely can be refined and optimized further.
> The changes needed for this task are closely related to those described in SCXML-197: Better separation of concern between SCXMLExecutor and SCInstance and introducing a new SCXMLExecutionContext.
> Although through SCXML-197 already many improvements are realized, to be able to implement the new SCXMLSemantics requires additional (major) changes, which functionally should be regarded part of SCXML-197, but cannot be committed separately as the changes are too closely related.
> I'll therefore update SCXML-197 describing those functional changes regarding the better separation of concerns, although they will be committed against this issue.
> An important note is that with the re-implementation of the SCXMLSemantics, the static SCXMLHelper class, as well as the (Transition) Path helper class functionalities will be completely 'absorbed' into the model and the new algorithm implementation. These classes therefore no longer are used and needed and will be removed. 
> Furthermore, the Step class now only is used from within the SCXMLSemantics implementation and therefore moved to the semantics package.
> With these changes in SCXML-196 and SCXML-197, the goals for Milestone 1 on the roadmap to SCXML 2.0 have been completely met and I'll create a milestone 1 svn tag for it shortly. 



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