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Revision as of 15:16, 17 March 2016 by (Talk | contribs) (Model)

ESON - EMF Simple Object Notation


ESON is a textual syntax for EMF models; like XMI is a XML-based syntax, ESON is a more human readable notation. It complements Xcore, which as a textual syntax for Ecore can define your EClass & Co.while ESON can represent their instances. (It is also possible to use ESON to create instances of non-Xcore normal/classic *.ecore.)

ESON is implemented based on Xtext, and *.eson files are thus truly textual representations; for example, changes made to your EObject are applied incrementally and preserve comments in or the formatting of the text. Crucially, users of ESON do *NOT* require any Xtext know-how or code generation for their Ecore models, because ESON is fully dynamic.

How to use


The easiest is to use the the usual menu Help > Install New Software... Add... Name: ESON, Location:

Or you can download the p2 ZIP named something like org.eclipse.emf.eson.repository-* from This ZIP can then be installed offline using e.g. the usual menu Help > Install New Software... Add... Archive.. (NOT Local..).

Alternatively do use the Eclipse Installer (Oomph) and choose the ESON project; this will get the source, luke, and you'll have a workspace ready made to contribute to ESON itself! See "How to contribute" below.


It's best to use the File > New > Example... > ESON to learn how to get started! Self explanatory? ;-)


EClass names can be fully qualified ("Library.Book {"), or import'd with the "use Library.* Book {" syntax. EObjects from other ESON can be similarly fully qualified ("author: lunar.loony"), or import'd with the "import lunar.* author: loony" syntax (this mechanism is based on Xtext's importedNamespace). (The "import" keyword should NOT currently be used for EClass, because its implementation as of 2015.05.19 only consults the Xtext index but does not consult the EPackage.Registry like the "use" keyword does, correctly.)

Editor UI

The ESON Editor shows the DSL source on the left, and a tree view of the model on the right. The Properties view allows to edit the currently selected node. Changes in any of these 3 parts are live auto synchronized to the other (without saving).

Double clicking on the background in source on the left or the tree on the right maximizes and hides the respective other part, double clicking it again restores the default split sash presentation.

There is a working inline Ctrl-O Quick Outline. The traditional read-only Outline view is intentionally disabled, to avoid end-user confusion with the right-hand side of the editor.

There is a File > New > Other > New ESON File wizard, which allows to choose the EPackage from drop-down. (It should also allow to then choose the root EClass, and fill in some default content - perhaps YOU will contribute that?)


Using ESON, any *.eson file can be loaded as a normal EMF resource. An instance of your "real" EMF model described by the ESON will be available in getContents().get(1); the get(0) will give you the internal Xtext representation which typically you won't be interested in. This resource has bi-directional synchronization of changes made to either of these two models - so you can use it like a "normal" EMF model, save it, and the ESON will be correctly updated.


In standard Xtext, IGenerator support is one per DSL language, registered in the respective *RuntimeModule. So one couldn't easily add an IGenerator for your ESON, unless you wanted to patch core ESON sources.

However, has added easy out-of-the-box support for plugging IGenerators into ESON. These can either be:

1. hosted in the run-time projects workspace next to the Test ESON, and registered via a src/META-INF/services/org.eclipse.xtext.generator.IGenerator Java Service Loader configuration files (thus don't need a separate development vs. hosted workspace);

2. hosted in the Eclipse plugin project, next to the Xcore (or Ecore) model, and registered via a standard Eclipse Extension Point offered by ESON.

The library example projects created by the ESON wizard illustrate this, including JSON and XML generation from ESON. (Remaining major issue is correct support for static Ecore/Xcore models instead of dynamic EMF instances; watch

Properties view customization

Since it is possible customize the Properties view. It's always shown tabbed, and by default with a "Basic" section showing all properties in flat list, similarly to the default EMF generated Properties. The library example projects created by the ESON wizard illustrates how to add your own custom tab sections with a simple example (in real world, perhaps you would like to use other EMF frameworks, such as EEF, to create your custom Properties views for ESON). The same eson.example project also shows illustrates how the default "Basic" section can be suppressed.

Known Issues, Curiosum & Noteworthy

The UI (default Tree Editor & Properties) does not yet support the usual add/remove + picker for multiplicity many references, only single ones. This is a UI limitation, the "back-end" (the code which synchronizes the two models) already supports it (DS-8674).

ESON supports EClass, EAttribute etc. names with dots in them (that is dots in the actual name, not dots to separate the name from the EPackage/s). Similarly, names (IDs) can consist of only numbers, or start with numbers. While neither is valid in standard ECore, it was added to ESON to support a particular use case.

How to contribute

Support Forum / Mailing List via Google Group!forum/eclipse-emf-eson-dev

Source code repository is Note branching strategy: master = stable (usually last released Xtext version), nightly = bleeding edge EMF & Xtext master (may be broken some times due to issues such as Xtext Bug 482033), Xtext-v* for maintenance of ESON on older Xtext releases.

Gerrit Code review on

Your contributions are more than welcome! Don't be shy.


The Eclipse Installer (Oomph) is great and the recommended way to set up your development environment for contributing to ESON (see bug 482099).

There currently is some small problem in the ESON Setup model causing Oomph not to automatically git clone and import (why??), so just manually clone the ESON Git repo yourself and then add as explained in the next paragraph. (This manual step would normally be not necessary; not clear why this doesn't work automatically anymore.)

In order to see and test changes made to ESON's Oomph Setup model org.eclipse.emf.eson.releng/ESON.setup in the workspace, remember that one first time you'll have to switch to make it use that, instead of the one from the remote Git repo which it originally used when installing (otherwise you just run the original Setup, without your newest local changes). This is done via "Import Projects..." in the drop-down of the Perform Setup Tasks reload action in the Oomph toolbar, or via the menu File > Import> Oomph > Projects into Workspace, and "Add user projects", then "Browse Workspace" to the local org.eclipse.emf.eson.releng/ESON.setup.

Note that as per this Oomph Forum discussion, it is recommended to set up separate installations for the 'master' vs. the 'nightly' streams.


ESON was originally born as, later re-incarnated on, and as of 2014-12 the project has been formally accepted and integrated as a sub-project of the official Eclipse Modeling Framework (EMF) on

Further Documentation

TBD Transfer, and update, old documentation from

Older doc:

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