EIS Patterns

This project aims to discuss and implement in dynamic languages Design Patterns for Enterprise Information Systems. The ideas here presented are discussed in more detail in the blog Enterprise Information Systems Development

Code is built on top of concepts borrowed from ERP5 Framework, sometimes interpreted in a different way.

Concept 1: Resource

Is anything used for production. It can be a material, money, machine time, human skills etc.

Concept 2: Node

Is something that transforms resources. For instance, a machine, a factory, a bank account.

Concept 3: Movement

Is a movement of any Resource from one Node to another.

Concept 4: Path

It describes how Movements are used to implement business processes.

ERP5 also has the concept of Item, an instance of a Resource. At the moment we decided not to use this concept, otherwise it would be necessary to create classes for instantiating the other 3 abstract concepts.

On the other hand, we introduce the concept of Connection, which is used to connect two movements, and can be used in one or more paths. There is a possibility of this concept become the Causality concept used in ERP5, but currently it is more generic than cause-effect relationships.

Concept 5: Connection

It describes the relationship between two Movements, in the context of one or more paths.

The core idea is to use the concepts as Lego parts. This mean not using subclasses in general, but masking the abstract concepts through configuration. For instance, a Movement is first configured as a concrete movement, such as transferring goods from supplier to customer. After that, it can be instantiated.

Of course, at some point it is necessary to implement specific functionalities for the concepts. These functionalities will be implemented in two places: a) At instances of concrete concepts, by defining specific behavior depending on different contexts (paths). b) At path objects, in the form of cordination code, which will make the path''s movements collaborate to realize a business process.

In term of process, the idea is to define a two phased one: a) Configuration: defines descriptors, which represent concrete uses of the abstract concepts. Descriptors list the types used to transform the abstract concepts into concrete ones. Configuration is done through a Domain Specific Language (DSL), having each concept a template text to be used for its configuration. In the future, we expect to define a proper grammar for this DSL. b) Implementation: uses descriptors to make the concrete concepts instantiable and implement the specific algorithms and data related to their concrete use. During the implementation of users stories, the callable objects refered above are implemented.

Thus, in a first moment, a domain specialist will configure concrete concepts using a specific DSL. Configurations are reused during the implementation, when user stories instantiates and define the specific behavior of the concrete concepts.

Programming Notes

a) Configurable attributes appear in the configure() method of every class, they are used to describe a concrete concept, thus their values are defined a priori, and obviously are the same for all object of this concrete. Therefore, they are stored as singleton objects refered by every instance of this concrete concept. Retrieval of these attributes is done by using mask and version as keys Attributes defined in the default constructors are those particular for each instance. A special case are the calable attributes of every class, which can also be reused by more than one object (see b). b) Every object has to implement a callable, for instance, the "use" method of Resource or "process" of Node. They can be used by one or more objects of the same concrete concept or even of different concepts. Ideally they can be define even at runtime and through configuration.

Setup

Pre-setup (on Ubuntu):

$ apt-get install python-setuptools
$ easy_install pip

Install dependencies (if needed) and run all specs (depending on your envirnoment, you'll need to call with sudo):

$ make

Run only unit specs:

$ make unit

Run only acceptance specs:

$ make acceptance