Re: database design method

Lauri Pietarinen wrote:
>Jan,
>
>> >
>> ><quote>
>> >
>> >6. D should provide some shorthand for expressing the generalized
>> >transitive closure operation, including the ability to specify
>> >generalized concatenate and aggregate operations.
>> >
>> ></quote>
>>
>> Strange, because in the prescriptions (thanks for the pointer, btw.) it
>> already says that recursion should be allowed. Any idea why then there is
>> still the need for an explicit transitive closure operation?
>>
>
>I don't necessarily have a complete answer for you but
>I could point out that the above "strong suggestion" talks
>about "providing some _shorthand_ for expressing the generalized
>transitive closure".
>
>Compare it to "Strong suggestion #2:"
>
><quote>
>
>2. D should include some declarative shorthand for expressing
>referential constraints (also known as foreign key
>constraints).
>
></quote>

Very good point, and it made me realize that I should have known the answer myself. The answer consists probably of two parts:

1. There are special efficient algorithms available to the query optimizer for the transitive closure. And because it is not easy for the optimizer to always recognize when a general recursive query computes a transitive closure it is useful if the user indicates this explicitly.
2. The same probabaly holds for the human reader who can now more easily understand what it is that is computed.
   • Jan Hidders