Start of factor graph port. Things don't work yet, but a lot of syntax updates towards PHP

PHPSkills/FactorGraphs/FactorGraphLayer.php

@@ -0,0 +1,67 @@
+<?php
+namespace Moserware\Skills\FactorGraphs;
+
+abstract class FactorGraphLayer
+{
+    private $_localFactors = array();
+    private $_outputVariablesGroups = array();    
+    private $_inputVariablesGroups = array();
+    private $_parentFactorGraph;
+
+    protected function __construct($parentGraph)
+    {
+        $this->_parentFactorGraph = $parentGraph;
+    }
+
+    protected function getInputVariablesGroups()
+    {
+        return $this->_inputVariablesGroups;        
+    }
+
+    // HACK
+
+    public function getParentFactorGraph()
+    {
+        return $this->_parentFactorGraph;
+    }
+
+    public function getOutputVariablesGroups()
+    {
+        return $this->_outputVariablesGroups;        
+    }
+
+    public function getLocalFactors()
+    {
+        return $this->_localFactors;        
+    }
+
+    public function setInputVariablesGroups($value)
+    {
+        $this->_inputVariablesGroups = $value;
+    }
+
+    protected function scheduleSequence($itemsToSequence)
+    {
+        return new ScheduleSequence($itemsToSequence);
+    }
+
+    protected function addLayerFactor($factor)
+    {
+        $this->_localFactors[] = $factor;
+    }
+
+    public abstract function buildLayer();
+
+    public function createPriorSchedule()
+    {
+        return null;
+    }
+
+    public function createPosteriorSchedule()
+    {
+        return null;
+    }
+}
+
+
+?>