Is there an agreed ideal schema for tagging

photos
  photoid
  caption
  filename
  date

tags
  tagid
  tagname

phototags
  photoid
  tagid

public static void threadproc_tags(object obj)
	{
		System.Web.HttpApplicationState app = (System.Web.HttpApplicationState)obj;

		SortedDictionary<string,List<int>> tags = new SortedDictionary<string,List<int>>();

		// update the cache
		DbUtil dbutil = new DbUtil();
		DataSet ds = dbutil.get_dataset("select bg_id, bg_tags from bugs where isnull(bg_tags,'') <> ''");

		foreach (DataRow dr in ds.Tables[0].Rows)
		{
			string[] labels = btnet.Util.split_string_using_commas((string) dr[1]);

			// for each tag label, build a list of bugids that have that label
			for (int i = 0; i < labels.Length; i++)
			{

				string label = normalize_tag(labels[i]);

				if (label != "")
				{
					if (!tags.ContainsKey(label))
					{
						tags[label] = new List<int>();
					}

					tags[label].Add((int)dr[0]);
				}
			}
		}

		app["tags"] = tags;

	}