Using the Xtend language for M2M transformation

In the last few month, we have been developing a customer project that centers around model-to-model transformation with the target model being AUTOSAR.

In the initial concept phase, we had two major candidates for the M2M-transformation language: Xtend and QVTO. After doing some evaluations, we decided that for the specific use case, Xtend was the technology of choice.

 

TopicExplanation
ComfortXtend has a number of features that make writing model-to-model-transformations very concise and comfortable. The most important is the concise syntax to navigate over models. This helps to avoid loops that would be required when implementing in Java


val r = eAllContents.filter(EcucChoiceReferenceDef).findFirst[
shortName == "DemMemoryDestinationRef"]
}
Traceability / One-Pass TransformationXtend provides so-called "create" methods for creating new target model elements in your transformation. The main usage is to be able to write efficient code without having to implement a multi-pass transformation. This is solved by using an internal cache to return the same target object if the method is invoked for the same input objects more than one time


However, the internally used caches can also be used to generate tracing information about the relationship from source to target model. We use that both for

  • Writing out trace information in a log file

  • Adding trace information about the source elements to the target elements


Both features have been added to the "plain" Xtend, because we can use standard Java mechanisms to access them.


In addition, we can also run a static analysis to see what sourcetarget metaclass combinations exist in our codebase.

PerformanceXtend compiles to plain Java. This gives higher performance than many interpreted transformation languages. In addition, you can use any Java profiler (such as Yourkit, JProfiler) to find bottlenecks in your transformations.
Long-Term-SupportXtend compiles to plain Java. You can just keep the compiled java code for safety and be totally independent about the Xtend project itself.
Test-SupportXtend compiles to plain Java. You can just use any testing tools (such as JUnit integration in Eclipse or mvn/surefire). We have extensive test cases for the transformation that are documented in nice reports that are generated with standard Java tooling.
Code CoverageXtend compiles to plain Java. You can just use any code coverage tools (such as Jacoco)
DebuggingDebugger integration is fully supported to step through your code.
ExtensibilityXtend is fully integrated with Java. It does not matter if you write your code in Java or Xtend.
DocumentationYou can use standard Javadocs in your Xtend transformations and use the standard tooling to get reports.
ModularityXtend integrates with Dependency Injection. Systems like Google Guice can be used to configure combinations of model transformation.
Active AnnotationsXtend supports the customization of its mapping to Java with active annotations. That makes it possible to adapt and extend the transformation system to custom requirements.
Full EMF supportThe Xtend transformations operate on the generated EMF classes. That makes it easy to work with unsettable attributes etc.
IDE IntegrationThe Xtend editors support essential operations such as "Find References", "Go To declaration" etc.

The Xtend syntax on the other hand is not a language based on any standard. But it’s performance, modularity and maintenance features are a strong argument for adding it as a candidate for model transformations.

Managing Autosar Complexity with (abstract) Models

A certain number of developers in the automotive domain complain that the introduction of AUTOSAR and its tooling increases the development efforts because of the complexity of the AUTOSAR standard. There is a number of approaches to solve this problem – one of the most used is the introduction of additional models.

The complexity of AUTOSAR

One often heard comment about AUTOSAR is that the meta-model and the basic softwae configuration is rather complex and that it takes quite some time to actually get acquainted with that. One of the reasons is that AUTOSAR aspires to be an interchange standard for all the software engineering related artefacts in automotive software design and implementation. As such, it has to address all potentially needed data. However, for the single project or developer, that also means that they will be confronted with all that aspects that they never had to consider. Overall, one might argue that AUTOSAR does not increase the complexity, but it exposes the inherent complexity of the industry for all to see. That however implies, that a user might need more manageable views on AUTOSAR.

Example: Datatypes

The broad applicability of AUTOSAR leads to a meta-model, that will take some analysis to understand. For application data types, the following meta-model extract shows relevant elements for  “specifying lower and upper ranges that constrain the applicable value interval.”

Extract from AUTOSAR SW Component Template

Extract from AUTOSAR SW Component Template

Which is quite a flexible meta-model. However, all the compositions make it complex from the perspective of an ECU developer. The meta-model for enumerations is even more complex.

2015-04-01_22h30_31

Extract from AUTOSAR SW Component Template: Enumerations

If you come from C with its lean notation

it seems quite obvious that the AUTOSAR model might be a bit scary. So a lot of projects and companies are looking for custom ways to deal with AUTOSAR.

Custom Tooling or COTS

In the definition of a software engineering tool chain, there will always be trade-offs between implementing custom tooling or deploying commercial tools. Especially for innovative projects, the teams will use innovative modeling and design methods and as such will need tooling specially designed for that. The design and implementation of custom tooling is a core competency of tooling / methodology departments.

A more abstract view on AUTOSAR

The general approach will be to provide a view on AUTOSAR (or a custom model) that is suited to the special needs of a given user group and then generate AUTOSAR from that. Some technical ideas would be:

“Customize” the AUTOSAR model

In this approach, the AUTOSAR model’s features are used to annotate / add custom data that is more manageable. This case can be subdivided into the BSW configuration and the other parts of the model.

BSW: Vendor specific parameter definitions

The ECUC configuration supports the definition of custom parameter definitions that can be used to abstract the complexity. Take the following example:

  • The standard DEM EventParameter has various attributes (EventAvailable, CounterThreshold, PrestorageSupported).
  • Let’s assume, that in our setting, only 3 different combinations might be valid. So it would be nice if we could just say “combination 1” instead of setting those manually
  • So we could define a VSMD that is based on the official DEM and have a QXQYEventParameter that has only one attribute “combination”
  • From that we could then generate the DEMEventParameter’s values based on the combination attribute.

This is actually done in real life projects. Technologies to use could be:

  • COMASSO: Create a Xpand script and use the “update model”
  • Artop: Use the new workflow and ECUC accessors mechanism

SYstem / SW Templates:

The generic structure template of AUTOSAR allows us to add “special data” to model elements. According to the standard “Special data groups (Sdgs) provide a standardized mechanism to store arbitrary data for which no other element exists of the data model.” (from the Generic Structure specification). Similar to the approach of the BSW we could add simple annotations to model elements and then derive more complex configuration for that (e.g. port communication attributes).

Adapt standard modeling languages

Another approach is to adapt standard (flexible) modeling languages like UML. Tools like Enterprise Architect provide powerful modeling features and the UML diagrams with their classes, ports and connections have striking similarities to the AUTOSAR component models (well, component models all have similarities, obviously). So a frequently seen approach is to customize the models through stereotypes / tagged values and maybe customize the tool.

The benefit of this approach is that it provides more flexibility in designing a custom meta-model by not being restricted by the AUTOSAR extension features. This approach is also useful for projects that already had a component-based modeling methodology prior to AUTOSAR and want to be able to continue using these models.

A transformation to AUTOSAR is easily written with Artop and Xtend.

Defining custom (i.e. domain specific models)

With modern frameworks like Xtext or Sirius, it has become very easy to implement your own meta-models and tooling around that. Xtext is well suited for all use cases where a textual representation of the model is required. Amongst others, that addresses a technical audience that is used for programming and wants fast and comfortable editing of the models with the keyboard.

German readers will find a good industry success story in the 2014 special edition of “heise Developer Embedded” explaining the use of Xtext at ZF Friedrichshafen.

The future?

AUTOSAR is a huge standard that covers a broad spectrum. Specific user groups will need specific views on the standard to be able to work efficiently. Not all of those use cases will be covered by commercial tools and innovation will drive new approaches.

Custom models with transformations to and from AUTOSAR are one solution and the infrastructure required for that is provided in the community project Artop and the ecosystem around the Eclipse modeling framework EMF.