In this paper, we propose a framework of faceted navigation over XML data. General faceted navigation schemes are used to browse objects (or records) containing multiple properties. However, because XML is semi-structured in nature, it is not straightforward to apply faceted navigation to XML data. Specifically, we need to cope with three major technical issues: 1) objects in XML data are not predetermined, 2) objects may have flexible and/or recursive structure, and 3) properties of an object need to be automatically detected and extracted. To these problems, in this paper, we formulate faceted navigation over XML data by giving definitions of class, property, object, and facet in XML data. We then formulate typical user interactions in faceted navigation as operations over aforementioned concepts (class, object, and facet). We also propose a framework based on these definitions and operations, and construct a prototype system based on the framework. Finally, we show experimental evaluations using the prototype system to show the effectiveness of our proposed scheme.