Re: Accuracer C/S Database?

From: Hannes Danzl (hannes_at_nexusdb.dbnexus.com)
Date: 12/13/04 

Date: 13 Dec 2004 12:46:33 -0800

Hello Alex,

> My point was not the concept is not similar but the difference in the
> features supported by the data dictionary. Though I do see a
> distinction worth mentioning - NXDB's data dictionary is related to
> the table while the Advantage data dictionary contains thing
> associated with managing the whole database which the tables are part
> of. Feature wise, you can correctly me if I am wrong.

there it's defintely different yes.

> As far as I
> know, NXDB does not support the features that I mentioned, i.e. view,
> stored procedures, RI, user, groups and permissions. There may be some
> basic permission related features in NXDB but not as extensive as in
> Advantage which support READ, WRITE, MODIFY, CREAT, DROP, ALTER and
> even column level permissions. And this can all be done using the SQL
> or API without making any change to the server.

RI is already stored there, the other things are coming with V2, whereas
not all is stored in the dictionary, as we decided to keep some of these
in dedicated system tables.
 
> Can you declare an RI programmatically using SQL or API without
> re-compile the server?

yes you can from API, not from SQL in V1 (or not fully at least - parts are
there). the server recompilation is only needed *once* to add the RI support
to the server. it adds another descriptor to the dictionary, which identifies
the class that implements the RI on the server. NexusDB is actually an almost
complete abstracted framework of classes. You can register any number of
named implementations of a certain base class (like record engine, index
engine, key engine, validation objects, ....). when opening a "table" the
header is read, in the header is the version, and the dictionary classname,
the server engine creates a dictionary instance of this class which then
reads the datadictionary, which in turn has the classnames for all the other
stuff. For example V2 can read V1 files not because they are 100% compatible,
but because V2 includes the V2 AND V1 implementations for the record engine
(which is responsible for interpreting a bunch of bytes as record and then
instantiating a field class which again interprets the actual field data).
when reading a table the dictionary knows the version it has to instantiate.
same goes for indexes or ri. it's only classes that are instantiated at runtime.
well that's the simple explanation. in reality it's a bit more involved

> Thanks for the clarification. You responded to Tim's post with
> unqualified yes's to all the differences he listed and declared that
> there is not many differences between Advantage and NXDB. I just want
> to support Tim's assertion. There are significant differences, at
> least with current versions of both products. We will see about the
> next version :)

sure are. at least in NxDB V1. V2 adds a lot of new stuff like PSM/SQL, SQL
2003, SQL Stored Procs, Full RI from SQL, ... just too many to mention. the
public beta is out since yesterday, but unfortunately our server is playing
up at the moment :((
 
> BTW, based on my unscientific sampling of your NG, I do think NXDB is
> a hugh improvement over FF quality and feature wise. Congratulations.

Thanks. And dont' take all the talk as "Advantage sucks". That's not what
we think or mean.

> I don't know if he still remembers but Geoff and I had a war of words
> over the quality of the FF a long time ago.

I'm sure he remembers. And i guess you were right as the FF quality was never
tooo good. Well not really bad either... 

--
  Hannes Danzl (hannes@nexusdb.dbnexus.com)
  Nexus Database Systems Pty Ltd
  (please remove the .dbnexus in the email to answer direcly)

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