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The FML language

FML (Flexo Modeling Language) is the language in which you describe a virtual model: the concepts it defines, what they know, what they can do, and which resources it federates. It is an object-oriented modeling language: a concept plays the part of a class, its properties are the attributes of the class and its behaviours are its methods. FML is also interpreted: a model is executed by the Openflexo runtime, which creates instances of its concepts and runs their behaviours.

Two things set FML apart from a general-purpose language:

  • It is statically typed, and the types reach outside the language. Every property, parameter and behaviour has a type, and the types offered by the technology adapters you use (a spreadsheet cell, an XML element, an EMF class…) are types of FML like any other.
  • Its instructions can act on external resources. Technology adapters bring their own operations, which you compose with ordinary control structures to read, create, update and delete data in the resources you federate.

Where to start​

  • Virtual models and concepts explains what a virtual model, a concept, a property and a behaviour are, without the syntax.
  • FML in ten minutes writes a complete, runnable model of about thirty lines, and explains each line.
  • Language tour follows a file from the top: its layout, namespaces and imports, the types it can name, and how a name is resolved inside a behaviour.
  • Declaring models and concepts covers annotations, nested and contained models, abstract concepts and inheritance.
  • Properties covers the kinds of properties, their initial values and how they are read and written.
  • Behaviours covers parameters, calls, creation and deletion, and events.

FML and FML-script​

Two textual forms share the same grammar:

  • FML (.fml files) defines a model: the concepts, their properties and their behaviours.
  • FML-script (.fmlscript files) drives the runtime: it loads resources, creates instances, calls behaviours and checks values.

This part of the guide is about the first one. FML-script only appears where an example needs it, to show the model at work.

About the examples​

Every example of this guide is a file that the automated tests of the platform load and run, checking each value the text states. A model shown on a page is the content of that file, without its header comment.