Concepts Fundamentals

This concepts page introduces the OpenPLX core workflow:

define models
declare typed attributes
instantiate and configure models
organize reusable structures

Minimal model

An openplx model is defined on root level in an .openplx file.

Let’s create an empty model.

MyFirstModel

MyFirstModel is a valid model, but it has no attributes defined, so it does not do very much.

Adding attributes

To add model attributes, we need to end the model name by a colon. And therefter add attributes indented by 4 spaces. The attribute type must be specified.

MyFirstModel:
    my_first_attribute is Real

Try:

1: Add the colon, but no attribute 2: Add the attrubute with name only 3: Try load the model above.

None of these three steps are valid. - What type of error do you get?

Error 1: Expected indented block and No model could be found Error 2: Expected an is keyword Error 3: Missing assignment MyFirstModel.my_first_attribute, owning model is not complete

For the model to be valid and therefore instantiable, values have to be set to all attributes. 3. above will therefore give you: Missing assignment MyFirstModel.my_first_attribute, owning model is not complete

Fixing the model

To make the model above valid, we may either specify a value for the attribute, or declare the attribute as optional

MyFirstModel:
    my_first_attribute is Real: 1.0

MyFirstModel:
    optional my_first_attribute is Real

Inheritance

OpenPLX models use single inheritance and traits.

Single inheritance

A model can inherit from another one, and therefore include all attributes of the parent model.

MySecondModel is MyFirstModel:
    my_second_attribute is Real: 2.0

Traits

If you like many models to share a set of attributes, you can define a reusable trait that can be used to inject a set of attributes.

trait ReusableAttributes:
    my_second_attribute is Real: 2.0
    my_third_attribute is Real: 3.0

This trait can then be used for any model, as long as it does not inject an attribute of an already existing name.

MyModelWithTraits is MyFirstModel:
    with ReusableAttributes

Which is valid, while:

MyModelWithTraits is MySecondModel:
    with ReusableAttributes

will give you an error: Symbol "my_second_attribute" already defined.

Expressions

Given the MyModelWithTraits with you have three variables that can be used to declare an axpression.

MyModelWithAnExpression is MyModelWithTraits:
    expression is Real: my_second_attribute + my_first_attribute - my_third_attribute