In modelling real-world knowledge, there often arises a need to represent and reason with meta-knowledge. To equip description logics (DLs) for dealing with such ontologies, we enrich DL concepts and roles with finite sets of attributevalue pairs, called annotations, and allow concept inclusions to express constraints on annotations. We show that this may lead to increased complexity or even undecidability, and we identify cases where this increased expressivity can be achieved without

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... increased complexity of reasoning. In particular, we describe a tractable fragment based on the lightweight description logic EL. Attributed Description Logics We introduce attributed description logics by defining the syntax and semantics of attributed ALCH, denoted ALCH @+ . Adding further constructs, e.g., for defining ALCHOIQ @+ , is easy given some basic familiarity with DLs [13]. We do not make the unique name assumption (UNA), as it can be enforced for individual names in the DLs we study. Syntax and Intuition We first give the syntax and intuitive semantics of ALCH @+ ; the semantics will be formalised thereafter.