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JWT Metamodel

Revision as of 09:30, 26 June 2008 by Marc.dutoo.smile.fr (Talk | contribs) (Imixs.org specific Action features support)

Introduction

This page describes the discussions and requirements for the meta-model of JWT. Based on the existing meta-model of AgilPro we will summarize all wishes, extensions etc. on this page.

An important part is JWT metamodel's extensibility.


Initial metamodel

This document File:AgilPro MetamodelDescription.pdf describes the metamodel of AgilPro as it is today (2007-02-21). This document will be the basis for discussions on all working groups who have requirements on the meta-model.

JWT metamodel comparisons

Comparison with other metamodels

A comparison with other meta-models as a result of an evaluation can be found in the following document: File:EvaluationExistingMetamodels.pdf.


Metamodel and XPDL 1.0

The document File:AgilPro Metamodel.pdf describes an initial revision of the document comparing the JWT/AgilPro metamodel with the XPDL 1.0 schema. It covers all the XPDL elements as well as the Bonita engine vendor specific extensions.

Metamodel and BPMN

Please find under File:Comparison JWT BPMN v0 3.pdf a document describing the differences between the JWT Metamodel on the one hand and BPMN on the other.


Requirements

Sources and contributors

List of requirements

BPMN2JWT transformation

Being able to store BPMN information that can't be mapped to JWT. This allows then to manipulate this information in JWT, but also to provide a perfectly bijective JWT2BPMN reverse transformation (notional "pivotal" metamodels). Marc : more generally, transformations to and from other models have the same kind of requirements.

Examples :

  • storing the "looping" boolean of BPMN Looping Tasks
  • storing STP BPMN Editor annotations, including those that may originate from other tools like STP-IM

Bonita v4 XPDL "hook" support

Hooks (as well as other Action-level features) should be stored in a Bonita specific metamodel extension. This extension should be typed so Bonita-specific UI extensions would know which metamodel extension they have to manage. This extension should be editable in a custom-built UI view.

Example : an Action may have Hooks. A Hook comprises the following information :

  • the Action-originated event (ready, start, beforeEnd, end, cancel, pause, resume...) it is hooked on. Note that a hook may be hooked on many events, which is the same that saying that there may be several identical hooks hooked on different events, since hooks are stateless.
  • the Java Hook class it calls when triggered. This class must implement the corresponding interface (NodeHookI, which has one method for each event).

Other examples :

  • action performers

Service (WebService, SCA) call support

Requires to store and manage information pertaining to these specific Actions / Application or Action / Application extensions.

WebServiceApplication has the following information :

  • WSDL definition and deployment information. A single service URL that also provides the WSDL by appending "?wsdl" to it is enough. Alternatively could be explicitely provided the WSDL, the service, the portTyp, the location in optional "overriding" properties.
  • operation
  • NB. there exists such a concept in the nowadays JWT metamodel, but it inherits from the Java specific Application whose "javaClass" and "jarArchive" are meaningless here
  • NB. this may be implemented in any given way at runtime, including on top of middleware technologies such as SCA. In this case, additional information required by the runtime implementation must be provided in a specific extension.

ScaServiceApplication has the following information :

  • SCA service name
  • SCA service Java interface. Ideally this should be guessed at runtime.
  • SCA service method
  • NB. the runtime engine must be integrated in an SCA architecture, typically by being configured to load at startup the appropriate SCA composite files. Note that the alternative of specifying in JWT a specific SCA composite file to instanciate at runtime is not a good SOA practice since it explodes the engine node's SCA architecture ; however it is interesting in a technical point of view, for example to implement calls made by other applications. like WebService calls.

Extension example : A runtime implementation of WebServiceApplication on top of SCA calls requires the following extended information (in addition to those of WebServiceApplication) :

  • SCA binding type. For a WebServiceApplication, must be "ws".
  • SCA service Java interface. Ideally this should be guessed at runtime.
  • other information required by the chosen runtime middleware
  • NB. these information allow to generate an SCA composite defining a java equivalent of the target web service, which may therefore be called.*
  • NB. these information could be provided in an extension to a given WebServiceApplication instance, or to an extension to Activity (i.e. process) that configures its runtime platform.

MWE Custom Action support

JWT users should be able to define custom Actions with custom metamodels, that might be exploited at runtime. Marc : I link this with the "black box Action" point of view, where Actions are merely linked blank "do something" slates that users implement at will ; this is similar to jBoss and Bull's PVM generic process engine, and somehow to Windows Workflow Foundation.

Such an extension is actually a JWT Action's implementation. This implies there can only be one such extension per Action, though nothing says they themselves can't be extended somehow.

Example : log Action

Example : POJO Action requires the following information :

  * POJO class
  * POJO method

Imixs.org specific Action features support

Imixs.org features depend on numerous Action-level properties that should be stored and accessible in JWT metamodel, and editable typically through an additional property tab(s).

Such an extension is actually an additional, activable feature on a JWT Action, that provides new functionality not related to the Action's actual implementation (i.e. what it does). More precisely, is is transversal in that it could as well apply to an Action that calls a web service, as to an Action that asks information to the user as event to a Join node.

Example : "IX Mail Module" which needs informations to generate a email during a transition, as seen here http://www.imixs.org/websites/imixs-org.nsf/vResourcesNameLookup/WorkflowModeler.CreateProcess/$FILE/img-0006.gif

JWT metamodel extension

Goals of JWT metamodel extension (consolidated)

  • allow JWT metamodel to be extended
  • 1. for JWT developers (ex. allow complex metadata, using static EMF for performances)
  • 2. for users : as easily as possible (ex. without writing java code, using dynamic EMF or XSD for ease of use, using simple concepts ex. a property map)
  • in multiple orthgonal ways (ex. "typed" extensions), so different extensions with different aims and features can coexist, and each of them can be easily found and distinguished by their management code and business logic
  • 3. IN A SECOND TIME (more complex, several consequences) provide ways to manage consistency of all typed extensions

JWT metamodel extension in the broader picture (added 20080527)

JWT metamodel extension has an impact on other JWT components : for example, it implies these components have to be extensible themselves, or they may benefit from custom tailored extensions. These components and their impacts are :

  • JWT Workflow Editor tool : model extension display and edition
  • JWT Transformations : extended model transformation to representation or executable format, enriching existing ones
  • JWT Runtime technologies : extensions that are custom to a given technology, extensible runtime utilities
  • JWT Workflow Administration and Monitoring tool : custom extensions, ex. to configure monitoring

Technologies

Here is a list of available technologies to extend the JWT metamodel :

  • static, "fixed" extension model done in static EMF (loaded as instances of JET-generated classes). Those classes must be available to JWT and specified in the workflow file. STP-IM -like properties are in this case. Christian Saad's proposition for the "dynamic properties" requirement also, but in order to control their semantics and behaviour, uses an additional metamodel that must be provided in workflow model, in workflow bundle, in autodiscovery directory or in plugin.xml.
  • custom designed extension model done with static EMF (loaded as instances of JET-generated classes). Requires the extension developer to generate classes using a .genmodel file. Those classes must be available to JWT and specified in the workflow file.
  • custom designed extension model done with dynamic EMF (loaded as instances of DynamicEObjectImpl). Ecore schema must be specified in schemaLocation and available there, or if loading is customized in workflow bundle, in autodiscovery directory or in plugin.xml.
  • custom designed extension model done with XML following user-defined xsd schemas, loaded as EMF / XML using through XSDEcoreBuilder. XSD schema must be specified in schemaLocation and available there, or if loading is customized in workflow bundle, autodiscovery directory or in plugin.xml. Alternatively but at the risk of lowering the typing of the whole model, any XML (without schema) could be allowed and loaded EMF / XML AnyTypeImpl. Alternatively, loading could be done not by base EMF but delegated to a custom EMF XMLHandler or even any non-EMF parser ; Imixs.org's Ralph Soika proposal follows this, and alternatively suggests that a model's extension content could even live in its own file.

Simple extension alternative : property map

No metamodel extension has to be defined. However there is no proper typing ; therefore property names are to be well managed so properties created by different extension vendors don't conflict with each other.

Powerful extension alternative : EMF extensibility and Aspects

Benefits from the full expressivity of Ecore metamodeling. The dynamic EMF technology is especially interesting, because it blends ease of use (no code to write or generate) with power ; therefore we'll especially consider it in our analysis from now on.

What parts of the model are interesting to be extended ?

  • Mainly Action, but possibly others :
  • external subprocess to add information about how to execute it
  • Model to add vendor-specific information about the process model
  • actually, any model element could be interesting to put Vendor specific information on.

Therefore we'll try to stay as open as possible on the topic of what is extensible.

Are there limitations ?

  • performances. Dynamic EMF and mixed static - dynamic EMF models are slower to load, in proportion to the amount of dynamic EMF within. Most extensions will be small and sparse, and therefore performances will stay OK. If not, it is up to the extension vendor to choose static EMF for his extension in order to provide better performances.
  • Diagram - graph - GEF manipulations. We choose to evacuate this problem by not letting extensions be displayed or handled in any way in the diagram GEF editor. Manipulating them in a generic or vendor specific view is enough.
    • Note that displaying them in GEF is still possible if the right GEF code is written - but that is more than a mere extension.
  • In the specific case of Action, Directly extending JWT Action is only possible using static EMF, because it may contain static subelements (Location, Size). So it is possible, but not the most useful. Anyway it is more akin to modifying the core JWT model than to writing an extension (I think), so we won't talk about this possibility here. However this still implies that EMF extensions should be put in their own subelement, meaning Action (or other extensible model elements) should have a containment relation to extensions.

There is a common concept that is philosophically close to our needs (anything extensible, extension in their own subelements) : the concept of "Aspect" (or mixin etc.). An Aspect can be viewed as a "part of a type" designed to answer or implement a well-defined business or technical need. Therefore I'll use the term of Aspect when speaking of typed extensions from now on.

Finally, EMF extensibility could also provide a simple extension alternative thanks to a base PropertiesAspectTemplate that has only to be extended.

Design alternatives

Here is a list of changes to the JWT model that are possible to implement said features.

"aspects" contained relation to EObject (better alternative : to Aspect) under ModelElement

  • we can't directly extend JWT Action, because it contains static subelements (Location, Size) and therefore can not have Dynamic EMF extensions. Therefore every extensions are put in their own subelement (below the "aspects" relation).
  • typing it with EObject makes it more powerful and easier to extend. However it does not take advantage of typing, allows "illegal" models (ex. adding a DataType as aspect...).
  • as a better alternative, it can be typed with a new Aspect class. In this case, we also create an Aspect class. Either Aspect is a static non abstract class, or a dynamic interface. The second is better because Aspect implementations will be loaded as DynamicEObjectImpl and not AspectImpl, and therefore fully dynamic ; but at the same time it forbids static EMF Aspect implementations.

Trying easy aspect sample

  • the goal of PropertiesAspectTemplate is to make simple extensions (i.e. property map like) trivial. It is an abstract dynamic object that has only to be extended by the user to create a custom property map aspect.
  • SamplePropertiesAspect is such a sample aspect providing information in the form of a mere property map

Trying STP-IM like inlined properties : "properties" contained relation to Property under ModelElement

Trying profiles idea :

  • Profile class with requiredAspectTypes multivalued attribute
  • "profileDefs" contained relation to Profile under Model,
  • "profile" (not contained) relation under Scope (limitation : not on Action ; though on StructuredActivityNode)

Weighting design alternatives

(This weighting is based on tries and samples)

Typing aspects relation to EObject (rather than Aspect) ? (added 20080527)

  • pros : allows to use Dynamic EMF (else not DynamicEObjectImpl) ; but maybe a DynamicAspectEObjectImpl could be written ?
  • cons : the outline > new child feature can't be used out of the box anymore, because all children are added as aspects (and not profiles, nodes...) ; but maybe relations (at least aspects) could be made visible there ?


JWT metamodel extension - working samples (added 20080527)

Required changes in JWT WE

These samples showcase the mixed static and dynamic EMF technology, thanks to a JWT metamodel with an EObject-typed "aspects" relation on ModelElement (or Action). To be loaded in JWT, it also requires some magic in WEEditor.createModel().

Extract from proposed JWT Metamodel :

<?xml version="1.0" encoding="UTF-8"?>
<ecore:EPackage xmi:version="2.0"
    xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="model"
    nsURI="org.eclipse.jwt" nsPrefix="">
  <eSubpackages name="core" nsURI="org.eclipse.jwt/core" nsPrefix="core">
    <eClassifiers xsi:type="ecore:EClass" name="ModelElement">
      <eStructuralFeatures xsi:type="ecore:EReference" name="aspects" upperBound="-1"
          eType="ecore:EClass http://www.eclipse.org/emf/2002/Ecore#//EObject" containment="true"/>
      ...
    </eClassifiers>
    ...
  </eSubpackages>
  ...
</ecore:EPackage>

Configuring EMF .workflow file loading in WEEditor.createModel() :

                  mainModelResource = getEmfEditingDomain().getResourceSet().createResource(resourceUri);
                  XMIResourceImpl r = (XMIResourceImpl) mainModelResource;
	          r.setEncoding("UTF-8");
	          // load options
	          r.getDefaultLoadOptions().put(XMLResource.OPTION_EXTENDED_META_DATA, Boolean.TRUE);
	          r.getDefaultLoadOptions().put(XMLResource.OPTION_USE_LEXICAL_HANDLER, Boolean.TRUE);
	          r.getDefaultLoadOptions().put(XMLResource.OPTION_USE_ENCODED_ATTRIBUTE_STYLE, Boolean.TRUE);
	          XMLOptions xmlOptions = new XMLOptionsImpl();
	          xmlOptions.setProcessAnyXML(false); // REQUIRED for XSD ; else won't find ecore classes defined in metamodel extensions ; however doesn't work with old agilpros
	          xmlOptions.setProcessSchemaLocations(true); // not required, works also with false ?!
	          r.getDefaultLoadOptions().put(XMLResource.OPTION_XML_OPTIONS, xmlOptions);
	          // save options (or in doSave())
	          r.getDefaultSaveOptions().put(XMLResource.OPTION_EXTENDED_META_DATA, Boolean.TRUE);
	          //r.getDefaultSaveOptions().put(XMLResource.OPTION_LINE_WIDTH, new Integer(80));
	          r.getDefaultSaveOptions().put(XMLResource.OPTION_USE_ENCODED_ATTRIBUTE_STYLE, Boolean.TRUE);
	          r.getDefaultSaveOptions().put(XMLResource.OPTION_SCHEMA_LOCATION, Boolean.TRUE); // REQUIRED else no xsi:schemaLocation after save !
	          //r.getDefaultSaveOptions().put(XMLResource.OPTION_SCHEMA_LOCATION_IMPLEMENTATION, Boolean.TRUE); // adds java:// schemaLocation for static ecore
		mainModelResource = getEmfEditingDomain().getResourceSet().getResource(
				resourceUri, true);
		// read version from the model object in the resource
		converter.readModelVersionFromFile(getModel(), resourceUri);
 
		// if old version model, reread it now that the version is known
		if (getModel() instanceof AnyType) {
			loadOldVersionModel(resourceUri);
		}

LogAspect sample

Here we define a LogAspect extension meant to provide an Action with additional information (messageFormat and logProtocol attributes) about how it might be logged at runtime.

Metamodel extension definition WEMetaModel_log1.workflow :

<?xml version="1.0" encoding="UTF-8"?>
<ecore:EPackage xmi:version="2.0"
    xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="logModel"
    nsURI="org.eclipse.jwt.log" nsPrefix="">
    <eClassifiers xsi:type="ecore:EClass" name="LogAspect">
      <eStructuralFeatures xsi:type="ecore:EAttribute" name="messageFormat" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
      <eStructuralFeatures xsi:type="ecore:EAttribute" name="logProtocol" lowerBound="1"
          eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"
          defaultValueLiteral="syslog"/>
    </eClassifiers>
</ecore:EPackage>

Workflow sample (inspired by a jwt2bpmn unit test workflow) activity_log1.workflow :

<?xml version="1.0" encoding="UTF-8"?>
<core:Model xmi:version="2.0" xmlns:xmi="http://www.omg.org/XMI"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:core="org.eclipse.jwt/core"
xmlns:organisations="org.eclipse.jwt/organisations"
xmlns:processes="org.eclipse.jwt/processes"
xmlns:log="org.eclipse.jwt.log"
xsi:schemaLocation="org.eclipse.jwt.log WEMetaModel_log1.ecore"
name="MainPackage" fileversion="0.4.0">
  <elements xsi:type="processes:Activity" name="Diagram1">
    <nodes xsi:type="processes:Action" name="Log Action" in="//@elements.0/@edges.0" out="//@elements.0/@edges.1" performedBy="//@elements.1" referenceEdges="//@elements.0/@referenceEdges.0">
      <aspects xsi:type="log:LogAspect" messageFormat="WARNING %" logProtocol="beep"/>
      <Location x="140" y="153"/>
      <Size width="71" height="31"/>
    </nodes>
    <nodes xsi:type="processes:InitialNode" out="//@elements.0/@edges.0">
      <Location x="41" y="158"/>
    </nodes>
    <nodes xsi:type="processes:FinalNode" in="//@elements.0/@edges.1">
      <Location x="294" y="157"/>
    </nodes>
    <edges source="//@elements.0/@nodes.1" target="//@elements.0/@nodes.0"/>
    <edges source="//@elements.0/@nodes.0" target="//@elements.0/@nodes.2"/>
    <references reference="//@elements.1" referenceEdges="//@elements.0/@referenceEdges.0">
      <Location x="164" y="56"/>
    </references>
    <referenceEdges reference="//@elements.0/@references.0" action="//@elements.0/@nodes.0"/>
  </elements>
  <elements xsi:type="organisations:Role" name="role" icon=""/>
</core:Model>


InvokeWebServiceAspect sample

Adding this aspect to an action (or its application) specifies a runtime invocation of the given web service.

Note that there will be two different ways to invoke a service : either explicitly calling a web service using this aspect, or calling a generic service and also specifying its binding (web service, rmi, xml / rest...) by using another aspect InvokeServiceAspect and runtime infrastructure provided by the friend SCOrWare project.

Metamodel extension definition WEMetaModel_ws.workflow :

<?xml version="1.0" encoding="UTF-8"?>
<ecore:EPackage xmi:version="2.0"
    xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="wsModel"
    nsURI="org.eclipse.jwt.ws" nsPrefix=""
    xmlns:core="org.eclipse.jwt/core"
    xsi:schemaLocation="org.eclipse.jwt/core java://org.eclipse.jwt.we.model.core.CorePackage">
  <eClassifiers xsi:type="ecore:EClass" name="InvokeWebService" instanceClassName="org.eclipse.jwt.we.model.core.impl.AspectImpl"
      eSuperTypes="java://org.eclipse.jwt.we.model.core.CorePackage#//core/ApplicationAspectTemplate">
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="bindingType" lowerBound="1"
        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="wsdl" lowerBound="1" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="url" lowerBound="1" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="operation" lowerBound="1"
        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
  </eClassifiers>
</ecore:EPackage>

Extract from workflow activity sample :

<elements xsi:type="processes:Activity" name="Diagram1">
    <nodes xsi:type="processes:Action" name="WS Action" in="//@elements.0/@edges.0" out="//@elements.0/@edges.1" performedBy="//@elements.1" referenceEdges="//@elements.0/@referenceEdges.0">
      <aspects xsi:type="ws:InvokeWebService" bindingType="ws" wsdl="" url="http://localhost:8080/EchoService" operation="echo"/>
      ...
    </nodes>
...
</elements>

Some screenshots : File:Jwt emfextension ws.png

UserMappingAspect sample

This sample showcases a more complex aspect.

UserMappingAspect's purpose is to allow to provide to an action (or its application) more specific user mappings than those defined globally at workflow level. It is useful when all applications executed by a workflow are not using the same user directory as the workflow engine ; in this case, applications that require specific credentials will use this aspect to provide them.

The UserMappingAspect contains several UserMappings, each specifying how a given runtime user (i.e. a user known within the workflow engine) is mapped to different credentials when talking to the application, which has to exploit this data on its own.

Metamodel extension definition WEMetaModel_usermapping.workflow (added 20080624) :

<?xml version="1.0" encoding="UTF-8"?>
<ecore:EPackage xmi:version="2.0"
    xmlns:xmi="http://www.omg.org/XMI" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore" name="usermappingModel"
    nsURI="org.eclipse.jwt.usermapping" nsPrefix="">
  <eClassifiers xsi:type="ecore:EClass" name="UserMappingAspect" instanceClassName="org.eclipse.jwt.we.model.core.impl.AspectImpl"
      eSuperTypes="WEMetaModel.ecore#//core/ApplicationAspectTemplate">
    <eStructuralFeatures xsi:type="ecore:EReference" name="userMappings" upperBound="-1"
        eType="#//UserMapping" containment="true"/>
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="enabled" lowerBound="1"
        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EBoolean" defaultValueLiteral="true"/>
  </eClassifiers>
  <eClassifiers xsi:type="ecore:EClass" name="UserMapping">
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="username" lowerBound="1"
        eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="password" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
    <eStructuralFeatures xsi:type="ecore:EAttribute" name="mappedUserName" eType="ecore:EDataType http://www.eclipse.org/emf/2002/Ecore#//EString"/>
  </eClassifiers>
</ecore:EPackage>

Extract from workflow activity sample (added 20080624) :

<elements xsi:type="processes:Activity" name="Diagram1">
    <nodes xsi:type="processes:Action" name="User Mapping Action" in="//@elements.0/@edges.0" out="//@elements.0/@edges.1" performedBy="//@elements.1" referenceEdges="//@elements.0/@referenceEdges.0">
      <aspects xsi:type="usermapping:UserMappingAspect" enabled="true">
        <usermapping:userMappings xsi:type="usermapping:UserMapping" username="guest" password="" mappedUserName="anonymous"/>
        <usermapping:userMappings xsi:type="usermapping:UserMapping" username="admin" password="admin"/>
      </aspects>
      ...
    </nodes>
...
</elements>

Some screenshots (added 20080624) : Jwt emfextension usermapping.png

Metamodel extensions and JWT WE (added 20080527)

Metamodel extensions and JWT WE - Issue

Or : how should the JWT Workflow Editor behave in the case of metamodel extensions ?

Now that we've got a basic idea of how it could work at model level, let's focus on what is its first use : display and edition in JWT WE.

As said before, we prioritize manipulating metamodel extensions in a generic (i.e. JWT outline and property view) or vendor specific view. It is enough and evacuates GEF diagram extension complexities. We will here focus on what JWT WE itself provides : the JWT outline and property views, and how it should best behave in the case of metamodel extensions.

NB. What is possible with extensions should be as much as possible specified in the ecore metamodel, since not only will it improve what features the generated EMF editors provide by default, but it will also prevent any illegal, non-conforming workflow model. However we obviously won't limit features to what EMF provides. So these needs could be additionally implemented through adapted or custom UI code or UI code generation, or even through ecore customization (see http://www.ibm.com/developerworks/opensource/library/os-eclipse-emfmetamodel/ - though wouldn't that impact dynamic EMF ?).

Metamodel extensions and JWT WE - functional needs

How do we want extensions / Aspects to behave in the Workflow Editor ?

Based on the previous metamodel extension ideas, and on trying things with the above sample and others, I've listed the following functionalities, from "most required" to "nice to have" ones :

  • "single" and / or "unique" : to limit instanciation of an aspect of a given type to at most one, or exactly one (i.e. pre-instanciated). Useful for all aspects that model "activable features".
  • (optional) "undeletable" and / or "readonly" : to forbid deleting it (or require it to be instanciated again).
  • "instanciation" : to require instanciation of an aspect or aspect list on a model element. This could be 1. a globally defined list, in JWT release configuration (or possibly user preferences ?) ; 2. a user-chosen list at model element instanciation time, by letting him chose an aspect list or a profile (aspect list)
  • "aspect choice list" : restrain aspect instanciation to at most one of a given list of aspect: "single" and / or "unique" property on an abstract Aspect that is a common ancestor to all aspects of the list ; ex. at most one aspect specifying what "does" a given Action, by making all such Aspect types inherit from the same ApplicationAspectTemplate, which has its "single" property set to "true", or making this abstract aspect inherit from ListConstraintAspect ; cons : requires to introspect inheritance to know the list
  • restrain an aspect type to be instanciated on model elements of a given type : using aspect subtypes, ex. ActionAspect, ModelAspect ; cons : complexifies aspect creation
  • other custom rules required by the extension developer

A gordian knot answer could be to

How to do it

  • solution 1 : by configuring those features in "special" properties of Aspects, like "singleton", "removable". For example, EMF / XML uses such special properties (ex. "xmlns:prefix"). However, these properties configure how the behaviour of the Aspect type (how it is instanciated etc.), and not of each of the Aspect instances, and therefore are not at the appropriate conceptual level, which complexifies their understanding.
  • solution 2 : modify ecore genmodel to store these information at the right conceptual level, and the EMF ecore JET templates to exploit them at generation time. However besides being difficult to do and maintain, it has not the level of flexibility we need : supporting new Aspect behaviours by adding new information there would be just as costly.
  • solution 3 : using a custom "metametamodel", that would also be in line with future jwt-views management, like Christian Saad advocates. Developing it in EMF would the development of an editor, while still allowing to package it in different ways : standalone, in a plugin.xml extension, or bundled within a .workflow.
  • other custom rules required by the extension developer would however require coding : either by implementing them in their own custom view UI, or by modifying EMF-generated code or generation templates (EMF.edit's ItemProviders), or even palette ? policies ??

Metamodel extensions and JWT Views

How do work JWT views :

  • edited in swing application jwt-view, by using the above cited code, using the ecore with harcoded path "jwt-we/src/org/eclipse/jwt/we/model/WEMetaModel.ecore" (but if there's none, allows to choose it) ; AppWindow saves the view name in the plugin*.properties files of jwt-we
  • handled in the org.eclipse.jwt.we.misc.views package of jwt-we : read by ViewResourceManager, Views, list of the read ecore's packages built by AnalyseEcore

Enabling metamodel extension at JWT views level (propositions) :

  • basis (works !) : Making it visible in the (outline) UI ! How : in Views.displayObject(), display by default (opposite of current behaviour), so model objects that are not specified in the view will be displayed. This is good behaviour, because, all default model elements will be specified in the view, and it is still possible to specify not to display one by setting it to false (unchecking its checkbox in jwt-view).
  • better : in jwt-view, allow to choose another ecore, many ecores, to merge their properties
  • later : change jwt-view to an eclipse plugin with an eclipse UI, make it the bases of the jwt-release-builder plugin

Metamodel extensions and JWT WE - finding and loading models and ecores

About extension loading among the various files, EMF has a lot of nice out of the box features.

  • For example, an EMF that refers relatively to an ecore extension will load right !
  • And EMF can be configured to load unknown extensions as XML without schema (concretely, the EObject implementation is AnyTypeImpl).
  • However it has limitations.

Limitation 1 : "unknown" extension ecores (i.e. not yet referred to in workflow models) are not available.

  • this requires a way for the end user to provide them in a simple way, like a standard directory whose ecores will be loaded at startup (csaad) ; and another way to add one at runtime, like a button "add extension model" allowing to choose an ecore file
  • vendors will want to be able to have a more built-in way to provide their ecore extensions, like a path in a plugin jar, if necessary referred to in their plugin.xml .

TODO consolidate and specify full behaviour for finding and loading models and ecore

Another issue is versioning extension metamodels and models (csaad)

  • a naming and versioning mechanism for extensions (a list of which must be centrally stored in the model file, e.g. in the model-element) to ensure compatibility.

Update algorithm

  • The update algorithm is for now limited to the "addition only" changes in the ecore.


Metamodel extensions and JWT Transformations

TODO

Metamodel extensions and JWT Runtimes

TODO


still TODO upload code in bugzilla

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