Re: To Normalize or not ??
- From: "Albert D.Kallal" <PleaseNOOOsPAMmkallal@xxxxxxx>
- Date: Wed, 8 Jun 2005 18:08:10 -0600
> A couple of points. You can't use Access with Wi-Fi? I'm not saying you
> can but I'd like to know why before I get myself into more trouble!
The problem is that when you run a split database (or even not split), you
in effect have a file OPEN across the wireless link. We all know that the
WORST thing that can happen is that while writing to a file, you turn your
computer off (in this case, you have a file open on your hard disk).
Often, the file will get damaged when you do this. Why? Because parts of
the file are in your computer memory, and as these parts are written to the
disk, the disk drive is in a vulnerable state, and if you stop this process,
then pieces and parts of the file DO NOT get written to the hard disk. They
get lost, and now you got a file on the disk drive with some pieces of the
file that got written, and some pieces that did not!
This is much the same idea when you turn off your computer, but forget to
save a word document (it is in memory, and thus does not get saved). The
problem here is than word is not so bad, because usually ALL of the document
is
loaded into memory. If you turn off the computer, not much happens, and you
loose your word document changes. However, when you got a file open like
ms-access, parts of that file are in memory, and other parts are actually on
the disk drive. And, some of those parts may need to be written back to
disk. And, if some of those parts don't make it back to the disk drive, then
you got a damaged file because certain pieces are needed to keep humpty
dumpy together. You turn the power off, and many of those pieces are
lost. Often the result is a damaged file. You see, the problem here is that
ms-access is different then excel or word. In ms-access, if you got 200,000
records, ms-access is smart enough to only pull in that ONE PART of the file
where the ONE record you need to edit out of the 200,000 records. (if
ms-access had to pull in the whole file each time..it would be slow as a
dog..and it is designed to be a high performance system, even when you got
200,000 records). So, only parts are moved from the file into memory.
Note that the exact same process happens when you open a file across a
wireless network. As it writes, parts of those pieces in memory may not
make it back to the disk drive due to a temporary cut in the connection.
When a temporary cut happens, pieces get lost, and further often when the
re-connection occurs, the system on the other end thinks that the file was
closed (after all, what can it think when the connection goes away?).
With a true client/server setup, if you are ordering a book on
www.amazon.com, and pull the plug, it would be laughable to think that this
would cause a problem on the Amazon site (it does not, because your computer
NEVER opens a file on their computers..but talks through a web site, and a
database server (which does in fact write to the file).
So, if you use a client to server (sql server, or the MSDE edition which in
included on the office cd), then those parts, and pieces of the file are
NEVER on YOUR computer, but those pieces and parts of the file most
certainly
are on the database server side. So, if you disconnect, or pull the plug on
your computer, those pieces of the file are sitting on the server side, and
thus no damage can occur. On the other hand, if while that database server
is updating and writing to its disk derive, and you pull the plug on that
server, the it is most certainly vulnerable to file damage...
> Also the term "Unbound Form" has come my way a couple of times today. How
> does one get the Info to stick or go to where it belongs, what happens to
> all of your queries and such. Also what are the advantages of this?
A un-bound form is simply a form where the datasouce of the form is NOT set.
This means you have to write code to fill the controls, and then when done,
take the data in the controls..and write the data back to the database.
>Also what are the advantages of this?
Well, since you are writing your own code, then YOU can choose as to when
the data will get written back to the table. You might want a complex un-do
feature, or simply not have the file update under certain circumstances. A
lot of VB developers use un-bound controls and forms. Further, VB6 does NOT
in
fact allow databound forms like ms-access. VB6 most certainly does have data
bound controls (you bind them to a datacontorl). Another advantage here is
that you can load up a form, and then disconnect from the database. This
tends to give you more reliability, as while the person is editing the
database, an active connection to the table is not needed. For this reason,
unbound forms can be more reliable then bound. However, when you throw in
the overhead of checking what changed on the form, and also the overhead of
re-establishing the connection, then often you don't save near as much in
terms of bandwidth, or even reliability here.
--
Albert D. Kallal (Access MVP)
Edmonton, Alberta Canada
pleaseNOOSpamKallal@xxxxxxx
http://www.members.shaw.ca/AlbertKallal
.
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