Abstract: Semantic categorization of data includes submitting obtained data values to a data enhancement service which has a semantic criterion for incoming data. A response from the service indicates whether the submitted data values meet the criterion, and is used to assign a likelihood that the values belong to a semantic category matching the criterion. Other semantic categorization operations do not necessarily use a data enhancement service. Some are based on which device was used to collect the data values, on a subject heading in which data was published, and/or on syntactic patterns. A semantic taxonomy shows semantic categorizations for one or more datasets and connections between datasets, possibly filtered per user request. Different versions of the taxonomy are stored for respective different users. Similarity between the data values can be assessed using semantic categorization. Taxonomies can be federated to allow exploration and understanding across multiple repositories.