Re: relational tables and objects

Dm. Arapov wrote:
>
>"Jan Hidders" <hidders_at_REMOVE.THIS.uia.ua.ac.be> wrote:
>
>> Dm. Arapov wrote:
>> >"Jan Hidders" <hidders_at_REMOVE.THIS.uia.ua.ac.be> wrote:
>> >>
>> >> Just for my understanding, your library doesn't provide persistency,
>> >> does it?
>> >
>> >The library neither provides persistency, nor prohibits it. It is
>> >parameterized with a class, which function is to provide implementation
>> >of tables. [...] Our design goal was to allow users have their own
>> >implementations of tables and indexes. RTL makes possible to have
>> >different implementations for different tables. [...]
>>
>> Ok. But would I then not also have to override/reimplement the relational
>> operators (like GROUP BY or JOIN) to take the specific implementation into
>> account?
>
>No, there is nothing to override there. Both operators are ready to use.
>(You can specify your own groupby functor, of course) Actually you can even
>use default table implementation, if you are happy with sorted vectors.

So the answer to my question is "yes". Note that the "then" in my question referred to "users have their own implementation" in your remark.

>> [...] Why would I use this library if I can use RDBMSs without the need
>> of filling in templates or defining derived classes?
>
>If you need full-scale DBMS, then you'll better use one. RTL is to help
>people with small needs. Say, inside a strategy game programmer needs to
>join tables, describing units positions, and then perform actions based on
>resulting relation.

In that case precomputing the join and storing it with pointers is probably going to be much more efficient and not much more difficult than modelling all the data in the relational model.

>In other words: "Do you need an 18-wheeler to ride to a grocery?"

Indeed, but the relational model was invented for large shared databases and that is not "driving to the grocery". So the question is why you think that it is appropriate for the applications you have in mind. What would for example be the advantage of using your library vs. simply modelling my data in an UML object schema and implementing those classes. Would that take a lot more time? Would the result be less efficient?

• Jan Hidders