Ideas on Enterprise Information Systems Development

This blog is devoted to ideas on Enterprise Information Systems (EIS) development. It focuses on Lean Thinking, Agile Methods, and Free/Open Source Software, as means of improving EIS development and evolution, under a more practical than academical view. You may find here a lot of "thinking aloud" material, sometimes without scientific treatment... don't worry, this is a blog!
Every post is marked with at least one of Product or Process labels, meaning that they are related to execution techniques (programming and testing) or management techniques (planning and monitoring), respectively.

Tuesday, March 22, 2011

Enterprise Information Systems Patterns - Part VII

Understanding how concepts are implemented
In Part V of this series, I used an UML Class Diagram to show the relationships among the framework's concepts. Although this diagram can help understanding these relationships, being it a class diagram, it also "says" that all concepts are "classes", which is not true. A better way for describing these relationships is using an ontology, as shown in Figure 1.
Figure 1: Ontology representing the relationships among framework's concepts

Operations, since they are immaterial resources, need to be realized by some active entity, in this case, by Nodes. Therefore, they are implemented as "functions" (in fact "methods"), instead of instances of a given class. Although in Python functions are also objects, one cannot define them as objects of a given business class. However, it is necessary to typify Operations somehow so that we can identify among some object methods which represent business operations. The solution for this is using Python Decorators, which are not exactly the same thing as the Decorator Pattern used in this framework. A Python decorator is a specific change to the language syntax that allows to more conveniently alter functions, methods, and classes.

Thus, it is possible to create a @operation(a_category) pythonic decorator which will store into method objects an attribute named category, with value a_category. In that way it is possible to mark methods as of Operation type, which is important to query a given class for its business skills. For instance, in a bank information system, it is possible to query a Credit_Analyst class to check which business operations objects of this type can perform. Or the contrary, using a keyword search discover, identify which methods of which classes may perform a given business operation. Moreover, I can create an ontology and navigate through it to check relationships among resources, nodes, and movements. With this ontology I can even suggest to a business analyst specific configurations for the system, given appropriate search terms.

Processes are sets of transformations and transportations, which in turn are used to encapsulate operations. Encapsulate means to forward calls to the appropriate Node subclasses methods - in fact to their Business Decorators methods - and log all information related to these calls, such as date and time, parameters and associated objects. Thus, Process objects implement the logic which coordinates how Nodes work. In other words, Processes implement workflows, which means, in turn, that the framework is process centric, or workflow centric.

Decorating, Decorating, and Subclassing
To make things more clear, let's call "decorators" the extension to Python syntax, and "business decorators", the classes created to decorate the framework concepts, as explained in Parts IV and V. Said that, let's check how the framework is implemented and extended:
a) Resources:
-Operations: methods, implemented into business decorators and marked with @operation decorator (yes, decorators for decorators).
-Work Items (formerly known as Materials): "classical" objects, for each new type of material, a new subclass of material is created.
-Kits: "classical" objects, for each new type of kit, a new subclass of kit is created. Given that kits can be composed by Operations, which are in fact methods, this composition is implemented through a list of references to these methods.
b) Nodes:
-All three subclasses are extend through business decorators. For instance, a person can be decorated by Developer (business) decorator to represent a software developer, or a Credit Analyst (business) decorator to represent a bank's credit analyst. No subclasses used. They can have methods related to @operations, to @rules of association (check Part VI), as well as methods representing internal machinery, in this last case, typically private.
c) Movements**:
-Transformations and Transportations are used as is, no subclassing, no pythonic decoration, no business decoration. They are used to build processes and store information related to operations calls, by encapsulating @operations during their configuration process.
-Processes are extended by mimicking workflow templates (current work), or by using workflow engines to make them work. A way of implementing processes is using Business Language Driven Development implemented through State Machine using decorators*.

For the reasons presented in Parts IV and V, subclassing is avoided at maximum - it is openly suggested only in the case of Work Items (Materials), which are considered passive "data bag" classes.

*Post-publishing note #1: we decided to develop our own State Machine code, and make it independent of this framework, check the Fluidity project.

**Post-publishing note #2: Transformations and Transportations are not classes anymore, as explained in Part XI.


  1. As of April 13, Material was changed to Work Item, a more generic term.

  2. In May 16th some small corrections and a reference to Fludity were applied to the post.