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Externalize Business Logic from Status/Transition handling of Business Entities

In any business domain, it is common to have a separate status life cycle for a domain entity. They are normally explained in a State Machine diagram which describes how a business entity responds to a business event. When it comes to implementation usually the status handling logic mixed up with the business logic code over Switch Statement style coding . Status life cycle handling for a domain entity within business logic would cause the application to be less manageable and more complex. Having a centralized mechanism of Status/Transition management would lead to a more flexible and manageable application. This will in turn allow the business domain expert and developers to easily manage state-transition of each domain entity with following potentials.

• Separate Business Logic from State-Transition handling logic
• Simply Read/Write access to the State Machine via a State-Transition Matrix model.
• Easy access of exception on undefined state-transitions.
• Directed application to Event-Driven approach.

The following diagram depicts the pattern how business service implementation is externalized the state transition handling.

State Machine will basically provide the state/transition handling services (load/reset state machine, get next status, set new status) to the Business Service layer which have no any knowledge about the logic of maintaining statuses for its entities.

State Machine Implementation

This idea is acquired from the mathematical modal called Deterministic Finite Automation on which Most of the commonly used compilers (Lexical Analyzer) are designed.

A state machine consists of

- a set of states S

- a set of transition T

- a state s₀ that is distinguished as the initial state

- a set of states F distinguish as final states

- and for each transition t₁, t₂ leaving state s as t₁ ≠ t₂

can easily be represented as a 2-dimentional matrix (2-dimentional array) in which one axis represents all possible state and the others for all possible transition, and returning resulting next state.

The following figure illustrates a sample state machine that follows above properties;

Here, how it represents above state machine in a 2-dimentional array.

int[][] stateMachine = new int[4][3];

stateMachine [STATUS_INIT][event_create] = STATUS_NEW;

stateMachine [STATUS_NEW][event_open] = STATUS_ACTIVE;

stateMachine [STATUS_ACTIVE][event_close] = STATUS_CLOSE;

stateMachine [STATUS_NEW][ event_close] = STATUS_CLOSE;

Using above state machine model, status handling services for the business service layer can be easily implemented as following.

load()

begin

//read from configuration or database and fill the stateMachine matrix

end;

nextStatus(event:Int, currentStatus:Int) : Int
begin

return stateMachine[currentStatus][event];

end;

I found this is simple way of expressing state machine for any business model and would lead to a centralized state management mechanism.

State Management in Business Entities

see http://neerosh.blogspot.com/2008/07/externalize-business-logic-from.html