The strengths of this model are that 1) it is based on utility maximisation, 2) it gives a first-order approximation to any demand system, and 3) by means of restrictions on parameters, it embodies and can test ideal properties of demand such as homogeneity of degree zero in prices and symmetry of reactions to price changes across commodities. The parameters a*, Yij> and Pi are, respectively, the share-specific constant, price effect and expenditure (or income)" effect. The more familiar properties of demand functions (price and income elasticities) are functions of these share parameters and other data.