The user may define subclasses of this class.
An external file may be referenced in a SAIF data stream or file. Information about such external data is provided through instances of this class. Instances of this class may be used in the following way:
The domain of an attribute in a user defined class is specified as ExternalReference. For example, in the definition of the class Employee as defined by a user, an attribute called photo may be of interest. Assume further that the employee photographs are stored externally in TIFF (Tag Image File Format) files and that there is no interest in transforming the images to SAIF. The domain for photo would be given as ExternalReference.
An instance of ExternalReference may be referenced. For example, in a SAIF data stream or file, the value for the attribute photo for an instance of Employee might be specified as an object identifier with a value of 27. In this case the value for objectIdentifier for an instance of ExternalReference, existing elsewhere in the SAIF data stream or file, is the integer 27. Alternatively, it would be possible to provide the values for ExternalReference directly, i.e. to embed them, without requiring the use of object identifiers.
address: the path and file name of the external file which is being referenced.
application: the name of an application which can read the file may be specfied. A spreadsheet file for example may be referenced and the name of the spreadsheet may be given under application.
comments may be given to provide further clarification.