A storage system comprises a controller; a memory; and one or more objects each including content data and metadata. The metadata is used to construct user-defined content properties, each content property providing an ability to extract a specific metadata field from the objects by referring to a user-defined content property name of the content property. The content properties are organized into user-defined content classes, each content class grouping a set of content properties into a named category under a user-defined content class name. The controller is operable to index the content properties of the content classes to create an index. The content properties being indexed are identified by the content property names. In some embodiments, the controller is operable to de-dupe the index, for content properties having same values expressed differently in different metadata formats, by directing the differently expressed values to same index field under same content property name.