In general, gateways insulate certain components of an IS from changes being made to other components. Gateways translate requests and data between the mediated components. Low level aspects of communication are more or less hidden. The following two-dimensional classification is based on the design of these two interactions. As mentioned above, this is not always possible.
Some gateways access the flat data files of the legacy IS directly.
This is only possible if the format of the data is known and the files are accessible. With sophisticated gateways only the format of the data in the files is described, queries are specified and output masks for the presentation of the retrieved data are designed. The queries are then interpreted in the gateway. As HTML is one dialect of SGML, such documents can be integrated into the W3 very easily. This is the most convenient approach and thus normally selected for new information systems.