L. Aversano, G. Canfora, A. Cimitile, D. Lucia, and A. , Migrating legacy systems to the Web: an experience report, Proceedings Fifth European Conference on Software Maintenance and Reengineering, pp.148-157, 2001.
DOI : 10.1109/CSMR.2001.914979

R. Banker, S. Datar, C. Kemerer, and D. Zweig, Software complexity and maintenance costs, Communications of the ACM, vol.36, issue.11, pp.81-94, 1993.
DOI : 10.1145/163359.163375

J. Bisbal, D. Lawless, B. Wu, and J. Grimson, Legacy information systems: issues and directions, IEEE Software, vol.16, issue.5, pp.103-111, 1999.
DOI : 10.1109/52.795108

M. E. Blume, Portfolio Theory: A Step Toward Its Practical Application, The Journal of Business, vol.43, issue.2, pp.152-173, 1970.
DOI : 10.1086/295262

E. Castro-leon, J. He, M. Chang, and P. Peiravi, The Economics of Service Orientation Available from: <http://www.infoq.com/articles/intel-services-economics>, 2009.

D. Cohen, M. Lindvall, and P. Costa, Agile Software Development, Data and Analysis Center for Software (DACS), 2003.

S. Cullen, P. Seddon, and L. Willcocks, Managing Outsourcing: The Lifecycle Imperative, MIS Quarterly Executive, vol.4, issue.1, pp.225-246, 2005.

J. S. David, D. Schuff, . St, and R. Louis, Managing your total IT cost of ownership, Communications of the ACM, vol.45, issue.1, pp.101-106, 2002.
DOI : 10.1145/502269.502273

N. Denzin, Sociological Methods: A Sourcebook. Aldine Transaction, 14 G.R. Gangadharan1, Eleonora J. Kuiper2, Marijn Janssen3, and Paul Oude Luttighuis4, 2006.

K. Erdil, E. Finn, K. Keating, J. Meattle, S. Park et al., Software Maintenance as Part of the Software Life Cycle, 2003.

L. Erikh, Leveraging legacy system dollars for e-business, IEEE IT Professional, pp.17-23, 2000.

A. Eastwood, Firm fires shots at legacy systems, Computing Canada, vol.19, issue.2, p.17, 1993.

G. R. Gangadharan, N. Kuiper, O. Luttighuis, and P. , Balancing Old and New in IT Budgets, 2010.

R. L. Glass, Software Conflict 2.0: The Art and Science of Software Engineering, 2006.

R. J. Gordon, Five Puzzles in the Behavior of Productivity, Investment, and Innovation, 2004.
DOI : 10.3386/w10660

J. Guo, Using Category Theory to Model Software Component Dependencies, Proceedings of the Ninth Annual IEEE International Conference and Workshop on the Engineering of Computer-Based Systems, Sweden, pp.185-192, 2002.

D. Hamilton, Linking strategic information systems concepts to practice: systems integration at the portfolio level, Journal of Information Technology, vol.14, issue.1, pp.69-82, 1999.
DOI : 10.1080/026839699344755

P. Heydebreck, M. Klofsten, J. Maier, and G. Hillenius, Innovation support for new technology-based firms: the Swedish Teknopol approach, R and D Management, vol.30, issue.1, pp.89-100, 2000.
DOI : 10.1111/1467-9310.00160

V. N. Iyer, Legacy Modernization, 2008.

M. Jeffery and I. Leliveld, Best Practices in IT Portfolio Management, MIT SLoan Management Review, vol.45, issue.3, pp.41-49, 2004.

C. Jones, Estimating Software Costs, 2007.

L. Kantner, R. Shrover, and S. Rosenbaum, Structured heuristic evaluation of online documentation, Proceedings. IEEE International Professional Communication Conference, pp.331-342, 2002.
DOI : 10.1109/IPCC.2002.1049115

R. J. Kauffman and J. Y. Tsai, When is it Beneficial for a Firm to Pursue a Unified Procurement Strategy for Enterprise Software Solutions?, Proceedings of the 42nd HICSS, pp.1-10, 2009.

B. Lientz and E. B. Swanson, Software Maintenance Management, 1980.

D. Linthicum, Enterprise Application Integration, 1999.

S. Lowe, Software Maintenance Pricing ? Fair or Out of Control? Available from: <http://blogs.techrepublic.com/tech-manager/?p=956>, 2009.

J. Martin and C. Mcclure, Software Maintenance: The Problem and Its Solutions, 1983.

S. Marwaha, S. Patil, and R. Tinaikar, The Next Generation of In-house Software Development, McKinsey Report, 2006.

F. W. Mcfarlan, Portfolio Approach to Information Systems, Harvard Business Review, vol.59, pp.142-150, 1981.

M. C. Ohlsson, A. Von-mayrhauser, B. Mcguire, and C. Wohlin, Code decay analysis of legacy software through successive releases, 1999 IEEE Aerospace Conference. Proceedings (Cat. No.99TH8403), pp.69-81, 1999.
DOI : 10.1109/AERO.1999.790190

D. Parnas, Software Engineering - Missing in Action: A Personal Perspective, Computer, vol.44, issue.10, pp.54-58, 2011.
DOI : 10.1109/MC.2011.268

O. Port, The software trap ? automate or else, Business Week, vol.3051, issue.9, pp.142-154, 1988.

W. Pree, Component-Based Software Development ? A New Paradigm in Software Engineering? Software Concepts and Tools, pp.169-174, 1997.

F. J. Reh, Key Performance Indicators ? How an organization defines and measures progress towards its goals Available from: <http://management.about.com/cs, 2012.

D. J. Reifer, V. R. Basili, B. W. Boehm, and B. Clark, Eight lessons learned during COTS-based systems maintenance, IEEE Software, vol.20, issue.5, pp.94-96, 2003.
DOI : 10.1109/MS.2003.1231161

J. Ross, P. Weill, and D. Robertson, Enterprise Architecture as Strategy: Creating Foundation for Business Execution, 2006.

I. Sommerville, Software Engineering, 2000.

A. H. Tsang, Strategic dimensions of maintenance management, Journal of Quality in Maintenance Engineering, vol.8, issue.1, pp.7-39, 2002.
DOI : 10.1108/13552510210420577

M. Turner, D. Budgen, and P. Brereton, Turning software into a service, Computer, vol.36, issue.10, pp.38-44, 2003.
DOI : 10.1109/MC.2003.1236470

W. Ulrich, The Evolutionary Growth of Software Engineering and the Decade Ahead, American Programmer, vol.3, issue.10, pp.12-20, 1990.

V. Vliet and H. , Software Engineering: Principles and Practices, 2000.

K. T. Yeo, Critical failure factors in information system projects, International Journal of Project Management, vol.20, issue.3, pp.241-246, 2002.
DOI : 10.1016/S0263-7863(01)00075-8

G. R. Gangadharan1 and E. J. Kuiper2, In what terms is the value of IT defined and quantified? 5. How do you quantify the value/benefits of IT systems versus expenses? 6. Are there also other ways (e.g. Balanced Score Card, Information Economics, Multi criteria, economic indicators such as TCO, ROI, etc. ...) used? Why are these ways (no longer) used?, Marijn Janssen3, and Paul Oude Luttighuis4 4