9.3 Rule Procedures

To define the contents of the approved list of verbs and objects, we will use word lists (see Section 8.3.5 "Word lists"). The definition of the rule including the word lists could look something like this:

<wordlist name="VerbList">
	<entry word="create"/>
	<entry word="read"/>
	<entry word="update"/>
	<entry word="delete"/>
</wordlist>

<wordlist name="ObjectList">
	<entry word="bank account"/>
	<entry word="customer"/>
	<entry word="credit"/>
</wordlist>

<rule name="ActionNames" domain="action">
   <description>Checks that action names contain only approved verbs 
      and objects.</description>
   <verbobject 
      term="name" 
      condition="!(_verb onlist VerbList) or !(_object onlist ObjectList)" 
      value="'Illegal name: '+name" />
</rule>

The procedure then has to extract the verb and object part from the result of the term expression, and pass the values as variables _verb and _object to the condition expression. If the expression evaluates to true, the procedure reports a violation, the value of the violation, as usual, given by the value expression.

Here is a possible implementation of such a rule procedure:

import com.sdmetrics.math.ExpressionNode;
import com.sdmetrics.metrics.*;
import com.sdmetrics.model.ModelElement;

01 public class RuleProcedureVerbObject extends RuleProcedure {

   @Override
02 public void checkRule(ModelElement element, Rule rule) throws SDMetricsException {

03    String name = element.getName();

04    ProcedureAttributes attributes = rule.getAttributes();
05    ExpressionNode term = attributes.getExpression("term");
06    Variables vars = new Variables(element);
07    if (term != null)
08       name = evalExpression(element, term, vars).toString();

09    int boundary = name.indexOf(' ');
10    if (boundary < 0) {
11       reportViolation(element, rule, "Element does not specify an object.");
12       return;
      }

13    String verb = name.substring(0, boundary);
14    String object = name.substring(boundary + 1);
15    vars.setVariable("_verb", verb);
16    vars.setVariable("_object", object);

17    ExpressionNode condition = attributes.getRequiredExpression("condition");
18    if (evalBooleanExpression(element, condition, vars)) {
19       Object value = getRuleValue(element, attributes, vars);
20       reportViolation(element, rule, value);
      }
   }
}

• 01: All rule procedure classes must have public visibility, a default or no-argument constructor, and extend the abstract class com.sdmetrics.metrics.RuleProcedure.
• 02: The base class defines the abstract method checkRule which we must override. Input parameters are the model element and the rule to check.
• 08: Here we evaluate the "term" expression, if defined. Method evalExpression evaluates a metric expression for a model element and returns its value. Metric expressions usually produce numbers (Float or Integer), strings, or model elements. In our example, the "term" expression should return a string.
• 11: We use method reportViolation when we detect the violation of a rule. We report the violated element, the violated rule, and a value describing the nature of the violation.
• 13-16: Here we extract the "verb" part and the "object" part of the term, and store them as variables "_verb" and "_object" for the evaluation of the condition expression in line 18.
• 19: Method getRuleValue evaluates the attribute "value" of the rule definition. We use this value to report the rule violation in the following statement.

<ruleprocedure name="verbobject" 
	class="com.acme.RuleProcedureVerbObject" />