This excerpt taken from the NDAQ 10-K filed Feb 27, 2009.
Amortization Periods of Intangible Assets with Finite-Lives
Intangible assets, net, primarily include exchange and clearing registrations, customer relationships, trade names, licenses and technology. Intangible assets with finite-lives are amortized on a straight-line basis over their estimated average useful lives as follows:
The estimated useful life of developed and new technology is based on the likely duration of benefit to be derived from the technology. We consider such factors as the migration cycle for re-platforming existing technologies and the development of future generations of technology. We also give consideration to paragraph 11 of SFAS 142, and to the pace of the technological changes in the industries in which we sell our products.
The estimated useful life of customer relationships is determined based on an analysis of the historical attrition rates of customers and paragraph 11 of SFAS 142, which includes an analysis of the legal, regulatory, contractual, competitive, economic, or other factors that limit the useful life of customer relationships.
See Note 3, Business Combinations, and Note 4, Goodwill and Purchased Intangible Assets, to the consolidated financial statements for further discussion of intangible assets.