The paper introduces Telos, a language designed to support the development of information systems by formally representing the relevant knowledge. Telos is based on concepts from knowledge representation and is suitable for representing knowledge about various worlds related to an information system, including the subject world, usage world, system world, and development world. The language features an object-centered framework for aggregation, generalization, and classification, a novel treatment of attributes, explicit representation of time, and facilities for specifying integrity constraints and deductive rules. The paper discusses the features of Telos through examples, focusing on metaconcepts that can be used to describe knowledge relevant to a particular information system. It also reviews actual applications of Telos and sketches a formalization of the language. The contributions of Telos include its ability to handle temporal knowledge, support for linguistic extensions, and integration with deductive databases for query processing and integrity enforcement. The paper concludes with a discussion of related work and suggestions for further research.The paper introduces Telos, a language designed to support the development of information systems by formally representing the relevant knowledge. Telos is based on concepts from knowledge representation and is suitable for representing knowledge about various worlds related to an information system, including the subject world, usage world, system world, and development world. The language features an object-centered framework for aggregation, generalization, and classification, a novel treatment of attributes, explicit representation of time, and facilities for specifying integrity constraints and deductive rules. The paper discusses the features of Telos through examples, focusing on metaconcepts that can be used to describe knowledge relevant to a particular information system. It also reviews actual applications of Telos and sketches a formalization of the language. The contributions of Telos include its ability to handle temporal knowledge, support for linguistic extensions, and integration with deductive databases for query processing and integrity enforcement. The paper concludes with a discussion of related work and suggestions for further research.