Assets

The accounting literature distinguishes between two approaches to define revenues:

an inflow concept

and outflow concept

The inflow concept of revenues defines revenues as an inflow or an increase in assets and reduction of liabilities arising from the operational activities of the firm. An inflow concept represents an asset liability approach.
The outflow concept of revenues defines revenues as an outflow of goods and services, or by the use of company's resources. The outflow concept follows the revenue-expense approach.
Asset liability approach measures income statement as a change in assets and liabilities. This approach is superior to revenue-expense approach, because assets and liabilities are real and income is determined by changes in net assets. Revenue-expense approach turns things other way around, and says that net assets are consequences of income measurement. Currently accounting system uses revenue expense approach to define income, where income is ...