public DecisionTree(string fileName) {
     _dataSet = new XmlToLinq(fileName);
     _trainingData = _dataSet.Rows;
     XAttribute newAttribute = null;
     _attributeList = new List<XName>();
     _expressions = new List<string>();
     foreach (XAttribute a in _dataSet.SampleRowElement.Attributes()) {
         newAttribute = new XAttribute(a.Name, "");
         _attributeList.Add(a.Name);
     }
     _targetConcept = _attributeList[_attributeList.Count - 1];
     
 }
		public ConceptLearner(string fileName) {
			_dataSet = new XmlToLinq(fileName);
			_trainingData = _dataSet.Rows;
		}