The content metadata directory system connects consumers of identified content to managed metadata databases and other digital resources. The system manages links between identifiers in content objects and metadata sources. It supports a variety of different type of content identifiers and allows for overlap among different content identification schemes. One method of associating a content object with metadata uses a combination of a content identifier and a bounding identifier to enable handling of disparate sets of content identifiers for content objects with potentially conflicting content identifiers. The method receives a content identifier for a content object from among a set of content identifiers and provides a unique bounding identifier for the set of content identifiers. This unique bounding identifier is used in combination with the content identifier to form a globally unique identifier for the content object. This globally unique identifier is associated with a metadata source, which enables routing of a user to the metadata source.