Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]
Date: Fri, 24 Jun 2005 08:39:43 +0200
In article <5eglb1ddsiq97jnpus1gotfapgdu3q8i21_at_4ax.com>,
> >I might agree that the model presented as a "pure object-oriented
> >database model" in the paper you mentioned is slightly different from
> >the (most common interpretations of the) network data model.
> In what they differ?
On reflection, the difference is less than on first glance, compared to the description of the CODASYL model in Tsichritzis and Lochovsky (1982). Instead of record types, records, data items and set types, Van den Bussche and Paredaens talks about classes, objects, functional properties and multi-valued properties. The difference, as far as I can tell, is that in the "OO" model, each object has an intrinsic ID of some sort that sometimes carries meaning, yet is not represented by a property.
This is just the structure, though. I haven't studied integrity and operators.
> >(Another point is the question of what "OO" in that context really
> >means---the paper does not mention encapsulation, polymorphism or
> It usually means user defined type support. OODBMS are network DBMS
> with some user defined type support.
As described, it has no more type support than CODASYL. You can define classes and decide what properties may apply to them, which corresponds to defining tables (record types) and links (set types).
-- JonReceived on Fri Jun 24 2005 - 08:39:43 CEST