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EMF DiffMerge/Model Patch


The modelpatch tool can create modelpatches based on the difference of two models, and it can later apply these patches on models.

EMF DiffMerge Patch UseCases.png

Model patch workflows

Patch recording from difference

The recording based on two versions of a model which versions are compared with EMF Diff/Merge. One of the versions will be the reference model and the other will be the target model. We create patch which can use to "upgrade" the target model to the reference model.

The EMF Diff/Merge calculates differences between the reference and target. The Patch Recorder processes the output of EMF Diff/Merge. It converts differences calculated by EMF Diff/Merge to patch entries, and - if necessary - it creates extra entries to save old features of objects and set new which are not represented in differences.

EMF DiffMerge Patch WorkflowPatchRecord.png

Patch application

There is two way for patch application:

  • You can directly apply the patch (or its reverse).
  • Patch will be applied over a copy of the model and you can explicitly select and merge changes through the compare view of EMF Diff/Merge.

Both ways support graceful degradation (report rejected entries). Patch modifications (filtering and reverse) are not parts of any of them, modifications are done on patch level, before application.

Direct patch application means that Patch Applier applies the patch directly over the selected model.

If you want patch application and comparison with EMF Diff/Merge the Patch Applier creates a deep copy from the selected model and applies sequentially all entries of the patch over this copy. The patched copy and the selected model are passed to EMF Diff/Merge which calculates differences for the changes. Necessary changes can be selected and merged explicitly through EMF Diff/Merge.

EMF DiffMerge Patch WorkflowPatchApply.png

Model patch representation

The Patch Representation contains an ordered collection of model patch entries and metadata information, such as author and time stamp. Model patch entries represent elementary model changes. Every entry has a direction (ADD or REMOVE) and a context identifier which identifies the modifiable element. We use three type of entries: (1) element entries, (2) attribute entries and (3) reference entries. Element entries represent an object creation (ADD) or an object removal (REMOVE). An element entry also stores the type of the element (as String) in both cases. We store the type even in case of removal to ensure the reversibility of the entry (if reverse patch is applied, a new object should be created). The two other type of entries (attribute and reference) represent modification of feature values. Both of them store the identifier of the feature which is modified and have an optional index attribute which represents the position of the value if the feature value is a collection. While an attribute entry stores the data type value as a string, the reference entry stores the identifier of the referenced object.

EMF DiffMerge Patch Representation.png


The following figure illustrates the modules of the model patch framework and their most important dependencies. The framework is divided into three parts: Patch Representation, Runtime API and Model Patch User Interface (UI). The Patch Representation ('patch') is completely standalone, without dependencies to Eclipse, EMF or EMF Diff/Merge. The Runtime API depends on EMF, EMF Diff/Merge and VIATRA runtime. The user interface extends the EMF Diff/Merge UI plug-in. There are persistence modules for storing patches in JSON and EMF model formats (the latter can be persisted to XMI).

EMF DiffMerge Patch Architecture.png


  • Build job: the location where the project is being built
  • EMF Diff/Merge: the host project that also provides the technological foundations upon which the Co-Evolution technology is based

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