[XmlRoot("FileGroupDatabase")]
public class FileGroupManager
{
    private List<FileGroup> _FileGroupList;

    [XmlArray("FileGroups"), XmlArrayItem("FileGroup")]
    public List<FileGroup> GroupList
    {
        get
        {
            return _FileGroupList;
        }
    }
}

public class FileGroup : FileGroupBaseAttributes 
{
    private List<File> _Files;

    [XmlArray("Files"), XmlArrayItem("File")]
    // the list of files in this group
    public List<File> Files
    {
        get
        {
            return _Files;
        }
    }
}

public class File  :    FileGroupBaseAttributes 
{
    // the full path of the file
    private string _Path;

    [XmlAttribute("path")]
    public string Path
    {
        get
        {
            return _Path;
        }
    }
}

public class FileGroupBaseAttributes
{
    // the list of tags for this item
    private List<string> _Tags;

    // the name
    private string _Name;

    // return a string that contains all the tags seperated by a space char
    [XmlAttribute("tags")]
    public string TagStr
    {
        get
        {
            // blah
        }
    }

    [XmlAttribute("name")]
    public string Name
    {
        get
        {
            return _Name;
        }
    }
}

<FileGroupDatabase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <FileGroups>
    <FileGroup>
      <Files>
        <File />
        <File />
        <File />
        <File />
      </Files>
    </FileGroup>
  </FileGroups>
</FileGroupDatabase>