vinay@cs.toronto.edu ("Vinay K. Chaudhri") (01/15/91)
Once an object taxonomy has been defined, how often does one need to change that information ? Is it reasonable to say that this information is equivalent to the schema information in relational datbases and thus will be hardly updated ? If the updates are required should they be on-line or off-line ? How frequent are the updates ? What are the good examples of such updates ? Should they be done one at a time or should be permmitted concurrently ? Your reactions on any of these questions will be highly appreciated. -- --------------------------------------------------------------------------- Vinay K Chaudhri Email: Mail:
sakkinen@tukki.jyu.fi (Markku Sakkinen) (01/15/91)
In article <91Jan14.165013est.7093@neat.cs.toronto.edu> vinay@cs.toronto.edu ("Vinay K. Chaudhri") writes: > >Once an object taxonomy has been defined, how often does one need to ^^^^^^^^^^^^^^^ (1) >change that information ? Is it reasonable to say that this >information is equivalent to the schema information in ^^^^^^^^^^^^^^^^^^^^^^^^ (2) >relational datbases and thus will be hardly updated ? ^^^^^^^^^^^^^^^^^^^^^ (3) By (1), do you mean only the inheritance graph between classes or the complete class definitions? If the latter, then you can well say (2), but that does not necessarily imply (3)! >If the updates are required should they be on-line or off-line ? >How frequent are the updates ? What are the good examples of such updates ? >Should they be done one at a time or should be permmitted concurrently ? Updating the definitions of classes while they have instances continues to be a hard and important research problem for OO databases. One not too difficult new paper by Staudt Lerner and Habermann is in the OOPSLA/ECOOP'90 proceedings: "Beyond Schema Evolution to Database Evolution". You can expect to find something in this area in the proceedings of virtually any recent database-related conference. Markku Sakkinen Department of Computer Science and Information Systems University of Jyvaskyla (a's with umlauts) Seminaarinkatu 15 SF-40100 Jyvaskyla (umlauts again) Finland SAKKINEN@FINJYU.bitnet (alternative network address)
sakkinen@tukki.jyu.fi (Markku Sakkinen) (01/16/91)
In article <1991Jan15.152723.3862@tukki.jyu.fi> I wrote: > ... >One not too difficult new paper by Staudt Lerner and Habermann >is in the OOPSLA/ECOOP'90 proceedings: "Beyond Schema Evolution >to Database Evolution". [...] Oops! It should have been "... Database Reorganization". Markku Sakkinen Department of Computer Science and Information Systems University of Jyvaskyla (a's with umlauts) Seminaarinkatu 15 SF-40100 Jyvaskyla (umlauts again) Finland SAKKINEN@FINJYU.bitnet (alternative network address)
ballou@databs.enet.dec.com (01/16/91)
In article <1991Jan15.152723.3862@tukki.jyu.fi>, sakkinen@tukki.jyu.fi writes: |> In article <91Jan14.165013est.7093@neat.cs.toronto.edu> vinay@cs.toronto.edu writes: |> [...] |> |> >If the updates are required should they be on-line or off-line ? |> >How frequent are the updates ? What are the good examples of such updates ? |> >Should they be done one at a time or should be permmitted concurrently ? |> |> Updating the definitions of classes while they have instances |> continues to be a hard and important research problem for OO databases. Two of the foundation papers in this area are: Banerjee, J., W. Kim, H.J. Kim, and H.F. Korth, "Semantics and Implementation of Schema Evolution in Object-Oriented Databases," Proceedings of ACM SIGMOD, San Francisco, CA, May 1987. Penney, D.J. and J. Stein, "Class modification in the GemStone Object-Oriented DBMS," Proceedings of OOPSLA '87, Orlando, FL, October 1987. Nat Ballou DEC OODB
tma@osc.COM (Tim Atkins) (01/25/91)
In article <91Jan14.165013est.7093@neat.cs.toronto.edu> vinay@cs.toronto.edu ("Vinay K. Chaudhri") writes: > > >Once an object taxonomy has been defined, how often does one need to >change that information ? Is it reasonable to say that this >information is equivalent to the schema information in >relational datbases and thus will be hardly updated ? > IMHO, no it is not like a relational schema in several important ways. First of all the relational schema is only indirectly representative of the real world situation being dealt with by applications. Only indirectly because it includes no notion of the functional aspects of the problem and because good relational design requires significant normalization that takes it even further away from the real world situation. Relational is a way of maximizing access to and security of data. Second, relational systems provide some means of ameliorating the need for change through the use of views that act somewhat like the data would if it had evolved. The OO equivalent is the subclass w/ dynamic binding of message implementations. While the latter is more powerful, it is by what you wrote a form of schema change. In the opposite direction another form of schema change takes place when further abstraction is employed. >If the updates are required should they be on-line or off-line ? >How frequent are the updates ? What are the good examples of such updates ? >Should they be done one at a time or should be permmitted concurrently ? > > >Your reactions on any of these questions will be highly appreciated. > The updates are likely to be extremely frequent in the design and tuning periods of a system. There may be, for some applications, periods where little or no change is needed. However, good general purpose classes may be useful in many applications and may require at least further speciali- zation as new applications come online. The updates should ideally be satisfiable on a running system. If this is not the case then OO techno- logy will not make it in 24 hour environments. Just supporting all needed forms of updates is a tough enough problem to occupy the industry for some time though, particularly in a persistent environment where existing objects and object identity must be maintained. - Tim Atkins