Re: Multiplicity, Change and MV
Date: 18 Apr 2006 06:32:10 -0700
> "dawn" <dawnwolthuis_at_gmail.com> wrote in message
> > x wrote:
> > It just struck me that you are bi-lingual with English as a 2nd (or
> > nth) language while I don't speak the RM as handily as MV, for example.
> > A minor challenge for both of us.
> I don't know "English" - the query language of some Pick system.
Yes, that is the Reality flavor of Pick, so many people still call the Pick query language English. Others call it Access, even though they clearly didn't end up on the winning side of that lawsuit. The fact that it has no name (many, many names) is one of the problems in even writing about it. The only name in common for all is the original spec name of GIRLS, which was a reuse, it seems of this acronym, so using that is not without problems either.
> > > I wonder if those who use them are confused by them or there are some
> > > precise definitions of them.
> > There are some terms with very precise definitions such as file,
> > attribute/field, value (on my site in the MultiValue triology,
> > particularly the Data "flashcards"), but since the model is not aligned
> > precisely with any single, simple, mathematical model, there is a lot
> > that is not nearly as precise as a mathematical definition would be.
The terms are just as precise as the words in the data in the database, however. As long as language is common to both, language is what is used to understand the system and to discuss any issues. Pick is based on the language of asking questions and getting responses, where XML is based on the language of documents. That is why there is more commonality between Pick and XML than between either of these and the mathematically-based (rather than language-based) SQL-DBMS systems.
> 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.
I don't know if that answered the question. Let me know if I missed the mark. Cheers! --dawn Received on Tue Apr 18 2006 - 15:32:10 CEST