We sketch a theoretical framework for the construction of evaluation schemes for web sites. The framework is based on the structure quite explicitly found in mathematics, physics and object oriented programming and it is determined by the relations between object domain, description language (theory) and method. Moreover, the framework also incorporates the distinction between different levels of description, the web site as a description of an object, the description of a web site as an object and the normative judgement of a web site. We present the structure of the framework and define and discuss briefly some of the basic concepts. KEYWORDS Quality, Evaluation and Assessment, Human Computer Interaction, Usability