private void GenerateProductNetwork(XmlWriter writer)
        {
            var items = categories.GroupBy(x => x.Project)
            .Select(x => new
            {
                Project = x.Key,
                Contributors = x.SelectMany(y => y.Contributions.Select(z => z.Contributor).Distinct()).ToList()
            }).ToList();

            // Setup reporting
            var totalCount = items.Count * items.Count * 3 / 2;
            var count = 0;
            var progress = 0;

            // Build grid
            var grid = new int[items.Count, items.Count];
            for (var row = 0; row < items.Count; row++)
            {
                for (var col = row + 1; col < items.Count; col++)
                {
                    var intersectCount = items[row].Contributors.Intersect(items[col].Contributors).Count();
                    grid[row, col] = intersectCount;

                    // Report
                    count++;
                    progress = count * 100 / totalCount;
                    ReportProgress(progress);
                }
            }

            // Setup header
            writer.CreateRow()
                .WriteCell(string.Empty);
            foreach (var item in items)
                writer.WriteCell(item.Project, true);
            writer.CloseRow();

            // populate data
            for (var row = 0; row < items.Count; row++)
            {
                writer.CreateRow()
                    .WriteCell(items[row].Project, true);

                for (var col = 0; col < items.Count; col++)
                {
                    if (col == row)
                        writer.WriteCell(string.Empty);
                    else if (col < row)
                        writer.WriteCell(grid[col, row].ToString());
                    else
                        writer.WriteCell(grid[row, col].ToString());

                    // Report
                    count++;
                    progress = count * 100 / totalCount;
                    ReportProgress(progress);
                }
                writer.CloseRow();
            }
        }