Changing the abstraction level
As expected, the high abstraction level brought by the use of only 4 concepts to try to define a whole system would bring side effects*. The basic one is that, if on one hand abstract concepts are highly reusable, on the other, they need to be extended a lot in order to become useful for representing concrete concepts, even the basic ones, such as Person or Product. I mean, a Node can be the abstract concept behind a Person object as well as a Factory object. However, you will need to provide a lot of extra code to make these concepts work. Given that I don't want to create lots of subclasses, the alternative is to use Decorators. However, in the same way, it is not good to abuse of a given technique, even if this technique is a well known design pattern. What I was going to do was create a lot of decorators instead of creating a lot of subclasses. In other words, I would be going against my main goal, which is to create a framework extensible by configuration, instead of programming.
Therefore, I stopped a bit to rethink the framework's abstraction level. One thing I realized is that it would be very hard to configure too abstract concepts, thus, by creating one more class level, I could find less generic but easier to reuse concepts. A side effect is that I can get rid of one more of the original concepts - Path. In other words, I shortened the width and broadened the length of the class hierarchy. The idea now is to use three classes: Resource, representing the production resources; Node, representing the entities that transform and transport these resources; and Movements, which represent transformations and transportations of resources. Each of these abstract concepts has three subclasses, representing two "opposite" concepts and an aggregator of these first two. Thus, the structure will be like this:
1)Resource()
-Material(Resource): product, component, tool, document, raw material...
-Operation(Resource): human operation and machine operation, as well as their derivatives.
-Kit(Resource): a collective of material and/or immaterial resources. Ex.: bundled services and components for manufacturing.
Comments:
a)Alternative terms such as Object (material) and Action (immaterial) can also be considered, however, the term Object can bring a lot of trouble in programming.
b)Another point is information, which is not material, neither it is something like operation. Document is used as the physical representation of information. c)Structural and Behavioral would be alternatives, however, they seem to be too academic to be used.
2)Node()
-Person(Node): employee, supplier's contact person, free lancer...
-Machine(Node): hardware, software, drill machine...
-Organization(Node): a collective of machines and/or persons. Ex.: manufacturing cell, department, company, government.
3)Movement()
-Transformation(Movement): an "internal" movement. Ex: transforming raw material, writing a report
-Transportation(Movement): a movement of resources between two nodes. Ex: moving a component from one workstation to another, moving a document from one department to another
-Process(Movement): a collective of transformations and/or transportations, in other words, a business process.
Comments
a) There maybe some confusion between Transformations and Transportations and Operations, but they represent different things. Movements use operations to transform or to transport resources. For instance, an industrial transformation uses a given machine operation during a given period of time to transform a given quantity of raw material into a component.
The next step is to define how to extend the basic concepts to make them work properly in concrete business processes representations, which will be discussed in the next post of this series.
* As I said in my first post of this series, if you need a "real-world" and flexible Python framework, give ERP5 - from which the basic ideas for this framework were taken - a try. Remember that this framework is a didactic one, therefore, some assumptions are simplified.
(The Change Log maps this series of posts to commits in GitHub)
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