Integration frameworks for building software engineering environments provide at least data, control and presentation integration facilities, together with integration devices which afford access to these facilities by the tools which populate the framework. Typically, an integration device is a specially developed language, or extension to an existing language, in which the integration programmer specifies the desired interactions between the tools comprising the software engineering environment. Surprisingly little effort has been applied to assessing the expressiveness of integration languages, even though the power of such a language limits the level of integration a tool can achieve within the environment. Our work seeks to provide an approach to both assessing and comparing the expressiveness of the integration devices of a range of commercial and research products. This paper presents a layered operational model, based on information structures; this model has been developed for describing the semantics of the inter-tool communication features of integration devices in a precise manner, and in a manner which will facilitate such assessment and comparison.