In this paper the principles of handling persistent objects in the object-oriented database programming language VML are presented. The main design criteria of VML with respect to persistence were: persistence independent programming, data type completeness and operations manipulating the extension of a class. After defining the above mentioned concepts an example is used to compare the modelling and computational power of VML with the database programming languages Adaplex, PS-algol, and Galileo. The distinction of types and classes is the basis for defining persistence in VML. Instances of classes are always persistent and those of data types are always transient. All instances are referenced by object identifiers, values of datatypes are referenced independently of the fact whether they are attached to persistent objects (and are therefore persistent itself) or whether they are stand alone".

Top