Re: MV and SQL
- From: "dawn" <dawnwolthuis@xxxxxxxxx>
- Date: 16 Jan 2006 09:52:55 -0800
x wrote:
> I have read the SOFA cards on your site
Great! I have some javascript user interface issues to address with
those yet, but the information is at least out there.
> and it seems that some of the
> features of a Pick MV system are:
> - dynamically typed data
Yes, I think that is an accurate term for it. It has a different
approach to typing, or lack thereof, than any other environment I've
been in. Everything is a string and you can convert it for output or
processing to another type (similar to casting it). But you are just
working with tag-delimited strings, somewhat like XML, but with
different programmatic structures (dynamic arrays sans metadata
compared to the DOM) to work with the data.
> - composed types definable by a regular language
> - procedural programming
The client/server tools do provide access from Java, VB, and other
languages, but the standard language used with the database for update
purposes is DataBASIC.
> - persistence of data and procedures/libraries
> - integrated development system
> - portability
> - parsimonious use of computing resources
as well as developer time. Highly flexible over time.
> I don't know anything about the "query languages" of these systems and their
> formal semantics.
The LIST statement mentioned in the SOFACards is analogous to the SQL
SELECT. The simple format is
LIST filename fieldname fieldname
It does not have only simple tables (rows & columns all populated) as
output, but includes output like the one that will be in the example in
my blog tomorrow.
> I'm particularly interested if they offer some kind of declarative query
> language.
Yes. Take a look at the poster at
http://www.tincat-group.com/mv/familytree.html Along the right hand
side are all of the names for this query language that I could find.
Oddly enough, this language is quite consistent across all of these
names, perhaps more standardized than SQL across vendors, although
there is no standards body (there was an attempt at such in the 80's).
Some people just call it ENGLISH, while most call it whatever their
preferred vendor calls it. For example, I use UniData from IBM where I
call it UniQuery and more recently OpenQM from Ladybridge Systems where
I think they call it QMQuery. I think it would be great if I could
refer to it by some one name. I was calling it MV Query, but there is
a product named mvQuery. Ugh.
> If you want to compare the "data models" you need to compare the LANGUAGES,
> not only the data structures.
Yes, indeed. I'm pretty sure I have a year's worth of blogs just on
topics related to data modeing.
> Some links that might interest you:
> http://en.wikipedia.org/wiki/Plural_quantification
> http://en.wikipedia.org/wiki/Second-order_logic
> http://en.wikipedia.org/wiki/Regular_language
I'll take a look. I haven't read these yet, but before I look at the
second order language link, I'll note that Monadic Second Order Logic
is provable, so it is not essential that a query language stick with
first order logic.
Cheers! --dawn
.
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