Re: Multiplicity, Change and MV

From: Bob Badour <>
Date: Tue, 18 Apr 2006 16:20:37 GMT
Message-ID: <pl81g.61748$>

x wrote:

> "dawn" <> wrote in message

>>x wrote:
>>>"dawn" <> wrote in message

>>>It just occured to me that other possible problem with MV systems beside
>>>loops might be the [im]possibility to represent relations over the same
>>>domain like r(A,A,A,A) where A is an element/entity/whatever like

> Courses,
>>>Lecturers etc.
>>>Could you provide an example for this ?

>>The domain for every (non-binary) attribute in Pick is String.
>>Everything else, such as indicating that the string is a Date, is a
>>description of the data.  A single value can be described as a Date and
>>as a String, for example.  There is no problem having a relation with
>>multiple courses.  Each course would be named differently and would be
>>a String.

> String is not an entity of the domain of discourse.
> I would like a detailed example as the one provided by B Faux.
> I can wait, so no hurry :-)

It's easy enough to construct your own example. Where he has PREREQUISITE, add a RECOMMENDED field for non-mandatory courses that the faculty suggest everyone take -- except those who are most confident in their ability. The example is easy enough to construct regardless whether PREREQUISITE and RECOMMENDED are both strings or both references to a COURSE file.

To elaborate, a course in vector calculus might not be a prerequisite for studying electric fields and waves, but speaking from personal experience, it sure is helpful to have taken one first.

The MV crowd would have you believe that one can create a database with single values, and when some user encounters a need for multiple values, the user can enter the data that way, while everything just continues to work. However, there are two logically distinct ways users could encounter that need:

  1. A lecturer teaches more than one course.
  2. A lecturer teaches a combined course.

This thread has already discussed case 1).

Case 2) might arise when some lecturer decides to combine vector calculus (VC) and electric fields and waves (EFAW) into a single lecture that grants credit for both courses. One could easily combine problem sets and tests to fully cover both curricula because EFAW uses so much VC. The students would have to buy both texts, and I suppose it would be easy enough to replace two 1-hour lectures with a single 90 minute lecture.

Data entry users at the university who encounter both cases have been told they can enter multiple values and everything keeps working. Users who encounter either case are likely to do the exact same thing, and of course, the query engine cannot interpret the same data two different ways.

As it happens, for identical queries, how Pick interprets the data differs depending on whether the COURSE domain is a string or a file reference, which is exactly the sort of thing casual users will not understand at all.

In fact, three years ago, I convinced myself that so-called experts, who the online Pick community actually considers experts, are incapable to understand this issue. Received on Tue Apr 18 2006 - 18:20:37 CEST

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