National Australia Bank's group executive for business banking, Joseph Healy, says the key to the future of business banking is to go back to the past. Healy is a great believer in the relationship management model and has spent the past two years fine-tuning that model at NAB.The results were on display yesterday, when the bank reported a 37 per cent increase in business banking earnings. It was the highest level of profit growth among the bank's seven divisions, and the $2.2 billion of cash earnings was close to half the group's total cash earnings.The division's net interest margin increased 16 basis points, from 2.35 to 2.51 per cent. Its cost to income ratio went against the trend for the group overall and fell 100 basis points from 31.5 to 30.5 per cent.In a market where business lending fell 3.5 per cent over the year to September, NAB's business lending grew 1.8 per cent. It increased its share of business lending through the year from 21 to 22.5 per cent.However, it did not do so well on the deposit side. Business deposits were up 9.6 per cent over the year, resulting in a fall in share from 21.1 to 20.9 per cent.Relationship management relies on accurate customer segmentation, so  customers get access to the appropriate level of contact with their manager. Healy said the way customers were segmented was often defined by a combination of measures such as business turnover and debt levels, and the bank's marketing objectives.Healy said: "Using turnover and debt levels means you miss the potential to do more business. It leaves a lot of money on the table. "A customer aspirations approach is a better indicator of the products and services the bank can bring to the relationship. We have launched a customer-led innovation strategy and over the next year 4000 of our business bankers will go through a training program with the goal of shifting the relationship model from one of knowledge to one of intimacy."The bank opened seven new business banking centres during the year and added 293 new business bankers.Healy said relationship management started to pay off after three years of a continuous customer/banker relationship. At that point the amount of cross-sell starts to take off. The challenge is to keep business bankers in their roles for that length of time."It is difficult to keep talented people in the same role for that long when the company encourages people to move through the hierarchy. We have looked at our incentive arrangements to make sure we can offer business banking as a career path."He said the other important part of the model was to take a community approach, which involves having bankers with credit authority on the ground in local business communities. Healy was also optimistic about the outlook for a revival in credit growth."It's actually got stronger in the second half, mainly in the larger corporate sector, the top 500 companies," he told yesterday's investor briefing.