private void loadModel(bool isSXFM)
        {
            OpenFileDialog pfd = new OpenFileDialog();

            if (isSXFM)
            {
                pfd.Title = "Select SXFM model";
            }
            pfd.Filter = "xml files (*.xml)|*.xml|All files (*.*)|*.*";
            if (pfd.ShowDialog() == DialogResult.OK)
            {
                System.IO.FileInfo fi = new FileInfo(pfd.FileName);
                if (isSXFM)
                {
                    GlobalState.varModel = VariabilityModel.loadFromSXFM(fi.FullName);
                }
                else
                {
                    GlobalState.varModel = VariabilityModel.loadFromXML(fi.FullName);
                }
                if (isSXFM)
                {
                    this.saveModelToolStripMenuItem.Enabled = false;
                }
                else
                {
                    this.saveModelToolStripMenuItem.Enabled = true;
                }
                this.saveModelAsToolStripMenuItem.Enabled         = true;
                this.editToolStripMenuItem.Enabled                = true;
                this.addAlternativeGroupToolStripMenuItem.Enabled = true;

                currentFilePath = fi.FullName;
                dataSaved       = true;

                InitTreeView();
            }
        }