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There are up to four integer-number Object Types associated with each observation, which encode a brief astronomical description of the data. At the moment we have identified some 150 astronomical categories which allow for both a very general typing ( e.g. `galaxy') or a more detailed ( e.g. Seyfert I) description.
Data can be selected on object type(s), and all catalogue entries with any of the (up to) 4 types matching the specification will be found. However, the object-type codes are put into the data base by the archive manager. Given the plethora of different objects in the catalogue (there are over 10000), this is a very substantial task, requiring much effort and time. Consequently, there will always be a substantial number of observations, which which have not yet been typed. Thus, searching the catalogue on object type may not reveal all observations of a given object.
Table lists some examples of object type codes; an archive user can obtain a complete list by using the SHOW command of the query software (section ).