In this paper we study dependencies of attributes in the context of Formal Concept Analysis. These dependencies allow to define a hierarchy of attributes reflecting the importance or interest in attributes. A hierarchy of attributes is a set of attributes partially ordered with respect to their importance. It represents domain knowledge used to improve lattice-based querying and navigation. Actually, in lattice-based querying, hierarchies of attributes are used to define complex queries containing attributes with different levels of importance: more important attributes define the focus of the retrieval while less important ones define secondary information whose presence is desirable in the answers. Furthermore, the relation between attributes in a complex query represents implicit or explicit knowledge units that must be considered while computing answers. Similarly, in lattice-based navigation, the choice of moving to a particular concept rather than to another is influenced by the higher importance of the attributes in the concept intent. Hence, the design and use of a hierarchy of attributes leads to a navigation guided by domain knowledge.