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Tracing Basics

Simple tracing is specified using trace directives, which all start with the word 'trace'. This is normally followed by the UML entity to trace (attribute, association, state, etc.).


Beyond, this, other clauses can be added to limit tracing to certain conditions, to switch on or off tracing in certain situations, and to specify data that will be output.


Each 'trace' statement emits exactly one trace record when something occurs to a matching UML entity; by default it is only changes in value that trigger emission of a trace record, but later pages describe how accesses to the value can also be traced. The format of the trace record will depend on the tracer being used but by default will contain the name of the entity and the new value of that entity.

The following are extremely simple example of tracing using MOTL on a UML Integer attribute. The default console tracer is used, so output will be sent to standard error.

Example


class Student
{
  Integer id;
  
  // Whenever the id attribute is changed, emit a trace record
  // The record will have the format id=value
  trace id;
  
  // The following Java main program can be used to demonstrate this in operation
  // This will output a record when id is set to 9.
  public static void main(String [ ] args) {
    Student s = new Student(6);
    s.setId(9); 
  }
}


      

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Another Example


class Student
{
  lazy Integer id;
  lazy name;
  
  // It is possible to specify multiple UML entities to trace as follows
  // It is also possible to indicate interesting information to record
  // in addition to the value of the element being traced
  trace id, name record "interesting behavior";
  trace id record "Even more interesting";

  // Traces will be triggered for each call to a 'set' method
  // and twice for id, since there are two trace statements for id  
  public static void main(String [ ] args) {
    Student s = new Student();
    s.setId(9); 
    s.setName("Tim");
  }
}


      

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