A model has to be written down somewhere, and every way of writing it down has a cost. XMI is exact and written for machines. YAML and JSON are friendlier, but they are data: no variables, no loops, no computation. Diagrams suit some models and not a model of four hundred rules. Generated editors are good for changing one element and poor for seeing the whole or reviewing a change.

A Groovy script that builds a model reads like a structured document, braces for containment and a call for each feature, and it is also a program. It can name things and refer to them with variables, repeat and compute, derive a model from a diagram, a spreadsheet or another model, and decide what saving the model means. It is text, so it is diffed, reviewed and merged like code.

One DSL for every metamodel

This book describes the Groovy module of the Nasdanika SDK Runtime, which loads a file such as library.ecore.groovy as an EMF resource. The language is derived from the metamodel by reflection when the script loads: every concrete class is a keyword, every feature is a call, and containment is nesting. Bind it to Ecore and you write metamodels; bind it to a rules or architecture metamodel and you write rule sets or architectures. Change the metamodel and the language follows on the next load, with no grammar, parser or code generator.

• The language: entry points, three ways to set a feature, variables and what a script produces.
• References by path, closure or variable, with names of classifiers and global objects.
• Deriving models from other resources, iterating them and copying prototypes.
• Saving: scripts that write themselves back, and the truncation trap to avoid.
• Errors and telemetry that point to the line of the script.
• A DSL for your own metamodel in two classes, with rule sets, handlers, capability factories and resolvers.

Who it is for

• Modelers who would rather write a model than click it together or read it as XMI.
• Developers who derive models from other models, diagrams, spreadsheets or systems, and want the derivation to be a file next to the model.
• Tool builders who want a textual surface for their metamodel without writing a language.

How it keeps you honest

Every listing is included from the module's sources, tests or test scripts and runs when the book is built. The book says plainly that a script model is a program that runs when it loads, so load scripts only from sources you trust. Status labels mark what is PLANNED.

This is a Nasdanika Zephyr Book, an in-depth manual for one module of the Nasdanika SDK Runtime, and it stands on its own. The code needs Java 25 and brings Apache Groovy 5; some familiarity with EMF helps. The text is licensed under CC BY 4.0 and the code under EPL-2.0.