Products are the physical object on which actuators apply transformations. They are also the source of data used by observers. Products are identified in the model by a unique identifier (usually a positive integer), called PID, or Product-ID.

Products record the various kind of transformations they go through: life-cycle event such as creation and disposal, the sequence of shape or space transformation (i.e. programs) that have been applied, and the sequence of assembly and disassembly applied.

It is important to record every step in the life-cycle of products, because the nature of a finished product depends of the kind of transformation applied, and also of their order. Furthermore, in an experiment aiming at verifying traceability features of a control system, the product history may be used as a mean of comparison.
Creation and disposal
Creation time is recorded in the ‘create_time’ attribute of class Product. Likewise, the time of disposal is recorded in the ‘dispose_time’ attribute. Before product’s disposal, this attribute is zero. When emulation stops, all products are disposed.
Shape transformation

Shape transformations are recorded in the attribute ‘shape_history’. This attribute is a list of tuples, each one representing a transformation.

These tuple have four elements:
  • the time of the transformation begining,
  • the time of the transformation end,
  • the name of the actuator doing the transformation,
  • the name of the program being executed.
Space transformation

Space transformation are recorded in the attribute ‘space_history’. This attribute is a list of tuples, each one representing a position change of the product. These tuple have two elements: * the time of arrival of the product in a position * the position: either the name of a Holder, or the name of a space actuator.

The sequence of position is continuous: if a product is in position P1 at t=2 and in position P2 at t=5 (no other position change being recorded between t=2 and t=5) we can assume that it was in position P1 from t=2 to t=5.


Physical Properties

Products have physical properties, such as their mass, length, or any other property useful to make the model work. Physical properties are implemented as items of the class Product. So if p is Product, p[‘prop’] is the property ‘prop’ of p.

These properties are initialized by create actuators, using the ‘physical-properties’ keyword (in the how field of the creation request). This key must point to a dictionary of the form key:’property name’, value: ‘property value’.
Modification of physical properties
Physical properties of products are modified by Shape Actuator (by definition of what shape actuators are). The list of modification is passed to the acturator using the ‘change’ field of the program that is executed. This key must point to a dictionary of change statements, in the form key: ‘property name’, value: ‘new property value’.
Getting product physical properties
The physical properties of the product being transformed can be used in the program delay, using the statement “product[‘property-name’]”. This statement is evaluated when running the program according to the current value of the product physical attribute. Likewise, this statement can be used when assigning a new value to a physical property So, “Program({‘change’: {‘length’: “product[‘length’]-1”}}, “product[‘mass’]”)”)”, is a program that decrement the physical property ‘length’, with a delay equal with the product mass.
Properties bound to other properties
Properties can be set as a function of other properties. To access another property in the evaluation context of a property, the statement self[‘propname’] shall be used. For example, the property ‘density’ can be defined as “self[‘mass’] / self[‘volume’]”. When the property is accessed, its value is computed. Circular references must be avoided, and cannot at the moment been detected.
Agregation and Composition of products

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