There are various definitions of what constitutes infrastructure, but generally infrastructure refers to the large-scale public systems, services, and facilities of a country or region that are necessary for economic activity. The sector tends to be separated into two broad subsets - economic and social. Economic infrastructure includes highways, water and sewerage facilities, and energy distribution and telecommunication networks whereas social infrastructure encompasses schools, universities, hospitals, public housing and prisons. Infrastructure assets are generally characterised by high development costs (high barriers to entry) and long lives. They are generally managed and financed on a long-term basis. Historically it was seen as the role of the government to fund and manage these assets for the good of the population. Today, the role of the government as the provider of public services is increasingly being questioned both in terms of the absolute cost to taxpayers and as to whether a government can deliver the assets as efficiently as a private company competing for the privilege. From the government's perspective there is a strong case for privatisation, where the debt raised by the private partner remains on their balance sheets, not on that of the Treasury's. These factors have resulted in a gradual migration from the public provision of infrastructure to the private sector. The private provision of these assets may take many forms from joint ventures, concessions and franchises through to straight delivery contracts. Essentially the private sector is being brought in to design, build, finance and/or maintain public sector assets in return for long term contracted payments from the government or access to the revenues generated from the asset.