SDMetrics User Manual - Set Procedures

SDMetrics - the UML design measurement tool

Contents > 9 Extending the Metrics and Rule Engine > 9.2 Set Procedures

9.2 Set Procedures

Defining set procedures is very similar to defining metric procedures. In the following example, we will implement a "conditional" set procedure that yields one of two possible sets based on a condition. The set procedure takes three required attributes "condition", "set", and "alt". If the "condition" expression evaluates to true, the set procedure returns the result of the "set" expression, otherwise the value of the "alt" expression.

   packacke com.acme;
   import java.util.Collection;
   import com.sdmetrics.math.ExpressionNode;
   import com.sdmetrics.metrics.*;
   import com.sdmetrics.model.ModelElement;
   
01 public class SetProcedureCondition extends SetProcedure {

    @Override
02  public Collection<?> calculate(ModelElement element, Set set)
         throws SDMetricsException {

03    ProcedureAttributes attributes = set.getAttributes();
04    ExpressionNode condexp = attributes.getRequiredExpression("condition");
05    ExpressionNode setExpr = attributes.getRequiredExpression("set");
06    ExpressionNode altExpr = attributes.getRequiredExpression("alt");

07    Variables vars = new Variables(element);
08    boolean condition = evalBooleanExpression(element, condexp, vars);
09    if (condition)
         return evalSetExpression(element, setExpr, vars);

10    return evalSetExpression(element, altExpr, vars);
    }
}

Some of the metrics engine API used here we already know from (Section 9.1.2 "Implementation of the Metric Procedure"), so we focus the discussion of this implementation on new features:

01: The class must have public visibility, a standard constructor, and extend the abstract class com.sdmetrics.metrics.SetProcedure.
02: The base class defines one method calculate. Input parameters are the model element and the definition of the set to be calculated (an instance of class com.sdmetrics.metrics.Set).
04-06: Method getRequiredExpressionNode returns the expression of the indicated attribute, or throws an SDMetricsException if the attribute was not defined. The message text of the exception is suitable to be read and understood by end users.
09-10: Method evalSetExpression evaluates set expressions for model elements, and returns a java.util.Collection with the set elements.

The return value of a set procedure can be a regular set (instance of java.util.HashSet), or a multiset (instance of com.sdmetrics.math.HashMultiSet). An "element set" (see Section 8.2 "Definition of Sets") will contain only instances of ModelElement. A "value set" will contain instances of java.lang.Number (Integer or Float), or strings. This set procedure can return either value sets or element sets, depending on the types of sets specified via the "set" and "alt" attributes.

For further examples on how to programmatically manipulate regular and multisets, see Section 9.6 "Set Functions".

To use our new set procedure, we register it with the metrics engine as follows:

<setprocedure name="conditionalset" 
   class="com.acme.SetProcedureCondition" />

Again, we deploy the class file of the procedure class in the "bin" folder of our SDMetrics installation (path com/acme/SetProcedureCondition.class). After that, we can write set definitions using the new set procedure. For example:

<set name="InterestingObjects" domain="class">
<conditionalset condition="'DataStore' in StereoTypeNames" set="AttributeSet" 
    alt="OperationSet" />
</set>

Note: every set procedure can also be used to define relation matrices (cf. Section 8.4 "Definition of Relation Matrices"). This includes custom set procedures you defined yourself.

Section 9.1.3 "Using the New Metric Procedure"

Contents

Section 9.3 "Rule Procedures"