Jjodel Language Family

Jjodel provides three complementary languages for working with models and metamodels. Each serves a distinct purpose along the purity-effect spectrum:

Language	Paradigm	Side effects	Primary use
JjEL	Functional	None	Querying, computing values
JjTL	Declarative	None (creates a new model)	Model-to-Model transformation
JjScript	Imperative	Yes (in-place mutation)	Metamodel editing

How they compose

JjEL is the foundation. Both JjTL and JjScript delegate all expression evaluation to JjEL. You write JjEL expressions inside JjTL transformation rules and inside JjScript commands.

JjTL and JjScript are independent of each other. JjTL transforms models declaratively (source model in, target model out). JjScript modifies the metamodel imperatively (create, rename, delete elements in place).

Both JjTL and JjScript support JjModal commands (prompt, confirm) for interactive, human-in-the-loop scenarios, and JjLet bindings (let $x = expr in body) for reusing computed values.

Design principles

All three languages follow the same design criteria, in priority order:

1. Maximum declarativity. Describe what you want, not how to compute it.
2. Minimum cognitive load. Few rules, minimal syntax, no boilerplate.
3. Maximum intuitiveness. Constructs read like natural language. Textual operators (and, or, not, implies), first-order-logic quantifiers (forall, exists), null-safe navigation (?., ??).

Where to use each language

Use JjEL in the Console to query models, in viewpoint templates to compute display values, and in validation constraints.

Use JjTL in the Transformation Editor to define model-to-model transformations with automatic traceability.

Use JjScript in the Console to create and modify metamodel elements, either manually or through the Jjodie AI assistant.

Next steps

• JjEL Reference for expression syntax and built-in methods
• JjTL Reference for transformation rules
• JjScript Reference for scripting commands