1. A method of managing metadata in a relational database system using a processor, the metadata created in a form of rough values corresponding to collections of values, wherein each rough value represents summarized information about values, wherein the values are elements of the corresponding collection of values, and wherein each rough value being substantially smaller than the corresponding collection of values, the method comprising: assigning a collection of values 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; forming a match granule containing summarized information about the assignment of the ordinal numbers of the elements in the collection of values to the structures in the structure dictionary; for each structure in the structure dictionary, forming a structure granule containing summarized information about one or more elements in the collection of values for which an ordinal number was assigned to the structure; and gathering summarized information represented by the match granule and one or more structure granules to form a rough value.
6. The method according to claim 1 , further comprising at least one of adding structures into and modifying the structures in the structure dictionary, and at least one of: immediately re-forming the rough values to reflect the at least one of the addition and modification; applying the at least one addition and modification to rough values corresponding to collections of values with new values inserted, or old values deleted or updated after said modification occurred, but not to already existing rough values; evaluating whether said addition or modification should be applied to re-form the already existing rough values based on a group of criteria including at least one of minimizing the cost of forming the structure granules corresponding to the added or modified structures and maximizing the estimated efficiency of using rough values while resolving queries, wherein the rough values are accessible independently from their corresponding collections of values, and the rough values are applied to minimize the amount of accesses to said corresponding collections of values while resolving queries; and providing an interface to a user of the system, said interface reporting the cost of forming the structure granules corresponding to the added or modified structures and the estimated efficiency of using rough values while resolving queries, wherein the rough values are accessible independently from their corresponding collections of values, said rough values are applied to minimize the amount of accesses to said corresponding collections of values while resolving queries, and said user is able to decide whether the modified structure dictionary should be applied to re-form rough values.