Meta-modeling Concepts ====================== The meta-meta-model in webgme describes the syntax for the meta-models. Below follows a short description and a video elaborating on each concept defined in the meta-meta-model. To follow this tutorial it is perfectly fine to skip **Sets**, **Mixins**, **Aspects** and **Constraints**. This entire section can also be seen as a reference manual and it's recommended to return to these when creating the meta-model. Containment ------------- * Defines where in the containment hierarchy a node can be created * One-to-many relationship - The cardinality can be restricted (e.g 0..* means any number of children) * All nodes have a parent - Except the ROOT node which is the root of the Composition Tree * Containment is a strong relationship: if a parent node is deleted so are all its children `Click here to open the video in a browser. `_. .. raw:: html

| | Base Relationship/Inheritance -------------------- * The base is a built-in pointer (one-to-one relationship) * All nodes have base pointer defined * All nodes (except the ROOT and FCO) have another node as their base - The FCO is the root of the Inheritance Tree (the ROOT lives outside!) * We can modify the value of base in the Meta Editor * The base/instance relationship is a strong relationship: if a base node is deleted so are all its instances * A node’s base is its prototype - Prototypal/Prototypical inheritance: asking for a property of a node traverses the base-chain till a value is reached `Click here to open the video in a browser. `_. .. raw:: html

| | Attributes ---------------------- * Textual or numerical information * Types: string, boolean, integer, float and asset - Assets can store a SHA-256 hash acting as an identifier for an artifact stored outside the model database * name is by default defined on the FCO - Is used to identify meta-nodes * Depending on the type, attributes can have different properties: - Default value - the value stored at the node defining the attribute - Read-only - the value can only be edited at meta-nodes - Enumeration, min, max, regex, multiline, etc. `Click here to open the video in a browser. `_. .. raw:: html

| | Pointers ------------- * Named one-to-one relation between two nodes, the owner and the target * Target of a pointer is either another node or NULL * base is a built-in pointer (inheritance) `Click here to open the video in a browser. `_. .. raw:: html

| | Connections --------------- * Not an actual concept of meta-meta-model * Using reserved named pointers, src and dst, we can create connections * Connections are a visualization technique on the canvas for nodes with pointers src and dst defined * We can assign attributes, children etc. to a connection and we can create any number of connections from/to a node * In the Property Editor we can see that it’s just two pointers * If any of the src or dst pointers are NULL, the connection appears as a regular box annotated with << Connection >> `Click here to open the video in a browser. `_. .. raw:: html

| | Sets -------------- * One-to-many relationship between a set owner and members * The cardinality can be restricted (e.g 0..* means any number of members) * Has special visualizer: Set membership - Similar to Composition - but members are visualized/edited * Meta-nodes are the members of the built-in set, MetaAspectSet, owned by the ROOT `Click here to open the video in a browser. `_. .. raw:: html

| | Mixins ------------ * Meta-nodes can be used by other meta-nodes as mixins * Meta-definitions are inherited from mixins - No actual data (e.g. attr values) of the mixin node is inherited * A meta-node can have more than one mixin (but only one base) - In case of colliding definitions, the base node has precedence - Collisions among mixins resolved based on GUID `Click here to open the video in a browser. `_. .. raw:: html

| | Aspects ------------ * Defines filtered views of your composition/containment (by selecting a set of valid children types) * Defined aspects show up as tabs in the Composition view `Click here to open the video in a browser. `_. .. raw:: html

| | Constraints ------------ * Functions defining constraints that cannot be captured by other meta-rules * Such custom constraints are evaluated at the server and by default turned off - To enable :code:`config.core.enableCustomConstraints = true;` * Constraints will be evaluated for every node that is of the meta-type where `Click here to open the video in a browser. `_. .. raw:: html

| | Meta Properties ------------------ Meta properties are properties that are typically set on meta-nodes with main purpose to guide/constrain the end-user while modeling. In contrast to the other concepts they are not defined using the Meta Editor, instead they are set in META tab in the Property Editor. .. figure:: meta_properties.png :align: center :scale: 100 % The META-tab in the Property Editor. isAbstract An abstract node cannot be instantiated or copied isPort A port node will visually be elevated to the border of its parent. validPlugins A list of plugins that can accepts the node as active-node. validVisualizers Which visualizers should be listed for the node and which one should be opened when navigating to it.