Abstract:
In a semi-structured database there is no clear separation between the data and the schema, and the degree to which it is structured depends on the application. Semi-structured data is naturally modelled in terms of graphs which contain labels which give semantics to its underlying structure. Such databases subsume the modelling power of recent extensions of flat relational databases, to nested databases which allow the nesting (or encapsulation) of entities, and to object databases which, in addition, allow cyclic references between objects. Due to the flexibility of data modelling in a semi-structured environment, in any given application there may be different ways in which to enter the data, but it is not always clear when the semantics are the same. In order to compare different approaches to modelling the data we investigate a measure of the information content of typical semi-structured databases in order to test whether such databases are information-wise equivalent. For the purpose of our investigation we use a graph-based data model, called the hypernode model, as our model for semi-structured data and formalise flat, nested and object databases as subclasses of hypernode databases.
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