An O ( n log n ) algorithm for the two-machine ow shop problem with controllable machine speeds

There appear to be some problems in defining direct marketing. Bauer and Miglautsch (1992) present direct marketing as a relational marketing process. According to Schofield (1995: 36), "Such a definition excludes much marketing work which employs individual direct marketing techniques on a pragmatic and eclectic basis, alongside nondirect marketing elements, and in which the use of such techniques is normally seen as direct marketing". He suggests that two definitions may be needed: a general, inclusive definition of direct marketing, e.g. the DMA-definition, which allows any use of any direct marketing technique to be recognized as an instance of direct marketing, and a definition of a direct marketing system, e.g. Bauer and Miglautsch''s definition, covering cases where a product or service is marketed exclusively by direct marketing methods (Schofield 1995: 37). This distinction suggests that several levels of direct marketing can be distinguished. The definition of direct marketing as proposed by Raaijmaakers et al. (1992) allows for distinguishing several levels of direct marketing without the need for more than one definition. They stress the importance of direct relationships and the specific use of marketing instruments. Based on their definition, four levels of direct marketing can be distinguished (Hoekstra 1994). Three of them concern strategic decisions and one is at the operational level (see table 1). These types cover the ever broadening field of direct marketing, including the direct marketing system as well as the use of direct marketing methods.