In a method for managing metadata in a relational database system using a processor, the metadata is created in a form of rough values corresponding to collections of values, wherein each rough value represents summarized information about values, the values are elements of the corresponding collection of values, and each rough value is substantially smaller than the corresponding collection of values. A collection of values is assigned to a structure dictionary, wherein each of the values represents the value of a row for an attribute and has a unique ordinal number within the collection, and wherein the structure dictionary contains structures defined based on at least one of interaction with a user of the system via an interface, automatic detection of structures occurring in data, and predetermined information about structures relevant to data content that is stored in the system. A match granule is formed, and for each structure in the structure dictionary, a structure granule is formed. Information represented by the match granule and the structure granules is summarized to form a rough value.