What is Meta-modeling? ====================== Alright, so you have created your first webgme project and probably want to make a bit more interesting than just containing the **FCO** and **ROOT** nodes... In a typical modeling environment (including the Design Studio you will have built up at the end of this tutorial) there will be a syntax or schema for how models can be constructed. In many tools this syntax is implied and enforced by the source code itself. But webgme, and meta-modeling tools in general, work differently. The rules for how models can be composed (structural semantics) is captured in a model itself - the meta-model. The following definition of meta-modeling is borrowed from Wikipedia [1]_. :: A metamodel or surrogate model is a model of a model, and metamodeling is the process of generating such metamodels. So a meta-model is a model that governs how other models can be composed. Simple Containment Example ------------------------- The domain, or meta-model, we are targeting in this tutorial is a domain for building electrical circuits. Two obvious concepts that comes into mind are the notions of a :code:`Circuit` and a :code:`Component`. * :code:`Circuit` - A diagram where different types of electrical-components will be place and wired together. * :code:`Component` - An abstract base type for various electrical-components such as :code:`Resistor`, :code:`Ground`, :code:`Inductor`, etc. Conceptually, just the notion of these two meta-types constitutes a meta-model. So far we have declared that our models can have instances of :code:`Circuit` and :code:`Component`, however nothing has been said about how such instances can be related to one another... A natural way of relating electrical-circuits and electrical-components is to say that circuits *can contain* components. Most meta-modeling environments have the notion of **containment** that defines exactly this. (It is typically visualized as an edge between the two types, where the end at the container is a black diamond.) .. figure:: containment_uml.png :align: center :scale: 40 % Containment as depicted in `UML `_ .. figure:: containment_webgme.png :align: center :scale: 100 % Containment as depicted in WebGME In the two graphical representations of **containment** the **cardinality** is also shown. For this example it says that there can be any number of :code:`Components` contained inside of a :code:`Circuit`. **Containment** is also a strong relationship. This means that when the parent (the container) is removed from the model so are the children. This suites well for electrical-circuits - if we discard a circuit the components are discarded as well. Model elements can be related in more ways than **containment**, in the next sections we will go through all the different meta concepts, meta rules, that webgme support. At this point you just need to have an idea of what meta-modeling is. .. [1] This tutorial uses the hyphenated version of meta-model and not metamodel.