Working with Bussiness Rule Engine --Soa 11g

Hi Guys

The Oracle Business Rules engine that comes as part of the SOA Suite provides a declarative mechanism for defining business rules externally to our application. This not only ensures that each rule is used in a consistent fashion, but in addition, it makes it simpler and quicker to modify. We only have to modify a rule once and can do this with almost immediate effect, thus increasing the agility of our solution.

In this article, we will introduce the new rules editor and look at how we can use it to define a decisions service to automate the approval of leave requests. Then, once we've done this, we'll see how to invoke the rule from the leave approval BPEL process.

 

Business rule concepts

Before we implement our first rule, let's briefly introduce the key components which make up a business rule. These are:

• Facts: Represent the data or business objects that rules are applied to.
• Rules: A rule consists of two parts, namely, an IF part that consists of one or more tests to be applied to a fact(s), and a THEN part that lists the actions to be carried out, should the test evaluate to true.
• Rule Set: As the name implies, it is just a set of one or more related rules that are designed to work together.
• Dictionary: A dictionary is the container of all components that make up a business rule. It holds all the Facts, Rule Sets, and Rules for a business rule.

Leave approval business rule

 To begin with, we will write a simple rule to automatically approve a leave request that is of the type Vacation and only for one day's duration. This is a pretty trivial example, but once we've done this, we will look at how to extend this rule to handle more complex examples.

Creating Soa Composite

Within JDeveloper, open up your LeaveApproval application . Open up the composite.xml file for the application and then from the Component Palette, drag-and-drop a Business Rule onto the composite.This will launch the Create Business Rules dialog, as shown in the following screenshot:

The first step is to give our dictionary a name, such as  LeaverequestRules, and a corresponding

In addition, we need to specify the Input and Output facts that we will pass to our decision service. For our purpose, we will pass in a single leave request. The rule engine will then apply the rules that we define and update the status of the leave request to either Approved or Manual

Next, click the Advanced tab. Here we can see that JDeveloper has given the default name LeaveApprovalRules_DecisionService_1 to our decision service. Give it a more meaningful name such as LeaveApprovalDecisonService.

Implementing our business rules

The rules editor allows you to view/edit the various components which make up your business rules. To select a particular component, such as Facts, Functions, Globals, and so on, just click on the corresponding tab down the left-hand side.

To add a rule, click the green plus symbol on the top-right-hand corner, and select Create Rule, as shown in the following screenshot (alternatively click on the Create Rule button, circled in the following screenshot).

For our leave approval rule, we need to define two tests, one to check that the request is only for a day in duration, which we can do by checking that the start date equals the end date, and the second to check that the request is of type Vacation.

To define the first test, click on &ltinsert test&gt. This will add the line <operand> = = <operand> under the IF statement where we can define the test condition.

The rule editor allows us to choose from the following action types:

• assert new: We use this to create and assert a new fact, for example, a new LeaveRequest. Once asserted, the new fact will be evaluated by the rules engine against the ruleset.
• modify: We can use this to either assign a value to a variable or a fact attribute; in our case we want to assign a status of Approved to the requestStatus property.
• retract: This enables you to retract any of the facts matched in the pattern (for example, TLeaveRequest) so that it will no longer be evaluated as part of the ruleset.
• call: This allows you to call a function to perform one or more actions.

The actions assert new and retract are important when we are dealing with rulesets that deal with multiple interdependent facts, as this allows us to control which facts are being evaluated by the rule engine at any particular time.

For our purposes, we want to update the status of our leave, so select modify

Calling a business rule from BPEL

Save the rule, and then switch back to our composite and double-click the LeaveRequest BPEL process to edit it. Drag a Business Rule from the BPEL Activities and Components palette into your BPEL process

Once we've specified the service, we need to specify how we want to invoke the decision service. We specify this through the Operation attribute. Here we have two options:

• Execute function and reset the session
• Execute function

If we choose the option Execute function and thus don't reset the session, if we were then to call the decision service several times within the same instance of our BPEL process, each new invocation would reuse the same session and would also evaluate facts asserted in any previous invocation. For our purposes, we just need to assert a single fact and run the ruleset, so accept the default value of Execute function and reset the session.

 We are ready to go with testing

In my next post we will discuss about Using Functions in BussinessRules

Happy Learning

                                                                                                                   By DeepthiReddy