Stevens (1989) suggests that companies integrate internally first, and then, extend
integration to other supply chain members. Companies usually follow an integration
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process that goes through three different stages. In stage I, there is no integration. In
stage II companies are internally integrated: their logistics activities are integrated with
the activities of other functional units, such as Purchasing, Production and Marketing.
And, in stage III, the internal integration achieved in stage II is extended to other supply
chain members, such as customers and suppliers.