Best practice for table design

[Debra Farnham]

Hello all

Windows 2K
Access 2K

I have designed a database which contains about six one to one
relationships. My original thinking was this design would keep the database
normalized in that it would eliminate blank fields and keep related data
together. Now that I have had time to reflect on it, I'm wondering if
perhaps I should have created one huge table. Even with the tables nicely
broken down, I can't avoid blank fields in some of them.

I'm really just looking for advice as to whether I have designed this
database in the best manner possible.

Any comments/suggestions would be welcomed.

Thank you in advance for taking the time to respond.

Debra

 

[Nikos Yannacopoulos]

Debra,

It's impossible for one to comment on a design they haven't seen at all!
However, ten bucks says "six one to one relationships" with "blank
fields in some of them" is an unnormalized database. If you post some
details of what you are trying to achieve (the overall concept) and your
current design, I'm sure you'll get some good advice here.

HTH,
Nikos

 

[Debra Farnham]

The database is maintaining a specific type of permit .... some details
apply to some of the permits and not others. (Pricing and charges for
example only apply to some of the services covered by the permit but not all
services apply to all permits).

There are no standard rates for any of the services that the permit may
cover.

Some of the details will be added in long after the permit is issued (i.e.
who installed it, who inspected it, the labour and material costs, etc.)

It is rare that all of the details will apply to all of the permits.

Some customers will do installations themselves and will be responsible for
their own costs in which case the permit will only allow for the work to be
completed and includes such details as address, permit applicant and permit
number.

I hope this provides the detail necessary to answer my initial query.

Thank you

Debra

 

[Debra Farnham]

I can provide more exact details (i.e. my current table design if necessary)
..... the way I'm seeing it though, its going to be difficult to avoid empty
fields whether it's one table or one hundred tables.

Thanks again

Debra

 

[Immanuel Sibero]

Hi Debra,
One-to-one relationship is very rare. Often, it is implemented for reasons
other than normalization. After reading the description of your problem, as
rare as one-to-one relationship is, your situation is one of them. Google
*subclassing in Access*, you will find many sources of information. Also
take a look at:

http://www.mvps.org/access/tables/tbl0013.htm

HTH,
Immanuel Sibero

 

[Debra Farnham]

Thank you kindly Immanuel!

I have visited the link you provided (as I have numerous times in the past -
not sure why I didn't think of that on my own).

However, I have done exactly as described and now feel confident in that I
have created my tables using the best model possible.

Thanks again for pointing me in the right direction.

Debra

 

[Immanuel Sibero]

You're welcome and good luck.


Immanuel Sibero

 

[Debra Farnham]

Immanuel

Do you have any idea how many one to one relationships isn't real good?

I think I have six of them in my database but they are all separate entities
as Rebecca describes in the sub-classing entities article.

I don't want to use subforms as I would have too many so I am using a single
query with all the necessary fields. The problem this has brought about, is
that I cannot later edit data in the form in fields that sit in a table
where no record was created initially (no record in the One side of the
relationship is the message I receive).

I hope this makes sense.

Any ideas?

Thanks again

Debra

 

[Nikos Yannacopoulos]

Debra,

Mail me your back acct details, IOU you ten bucks! Playing with the odds
doesn't always pay.

Nikos

 

[Debra Farnham]

Hi Nikos

Here's my current table design

tblWorkOrders
dtmDateofPermit
strWorkOrderNumber
lngApplicantID
strRoadOpening
strPermitNumber
memServiceLocations
lngCityID
memAdditionalInstructions
ysnDrawingApproved
curEstimatedCost
strPONumber
lngIssuedBy

tblApplicant
autApplicantID
strApplicantName
strAddress
lngCityID
strPhone
strPostalCode

tblCity
autCityID
strCity

tblMainToLot strSize
ysnWUCInstall
ysnCustomInstall
ysnPressureTest
ysnServiceLot

tblWorkOrderDetails
strWorkOrderNumber
ysnUseof Hydrant
ysnAnnual
lngSizeofConnection

tblSizes autSizeID
strSize

tblInspectionDetails
strWorkOrderNumber
ysnInspectOnly
lngSizeID
ysnTap&InspectOnly
lngSizeID
ysnPressureTest
ysnChlorinate
ysnFlush

tblLotToBuilding
strWorkOrderNumber
ysnWUCInstall
ysnCopper
ysnCustInstall
lngSize
ysnPVC
ysnNewService
ysnRenewal

tblDistribution
strWorkOrderNumber
lngInstallerID
lngForemanID
dtmCompleted
strRequisitionNumber
ysnAbandonedService
dtmDateAbandoned

tblInstallers
autInstallerID
strInstallerFirstName
strInstallerLastName

tblForemen a
utForemanID
strForemanFirstName
strForemanLastName

tblFinance
strWorkOrderNumber
curLabour
curMaterial
curTrucking
memOther
curOtherCost
strDebit
strCredit
strInvoiceNo

tblCharges
strWorkOrderNumber
ysnSize
cur929729865
curPressureTest
cur929729906
cur929729881
curDeposit
curCurbBoxDeposit
curVISIDeposit
cur909820350
strChequeNumber

tblIssuer
autIssuerID
strIssuerFirstName
strIssuerLastName

tblInspection
strWorkOrderNumber
ysnMaterial
strDepth
ysnPressureTested
ysnChlorinated
ysnDeficiences
lngInspectorID
dtmInspectionDate
memComments

tblInspectors
autInspectorID
strInspectorFirstName
strInspectorLastName

The only table that will ALWAYS have data in all fields initially is
tblWorkOrders. At some point, further details MAYbe added to tblInspection
or tblIssuer. I think that the lookup tables speak for themselves. Thank
you for taking the time to review my design.

Debra

 

[Nikos Yannacopoulos]

Debra,

What can I say, other than apologize for making you go through the
trouble of typing all this (I hope you just copied / pasted from
somewhere!)... my previous post was just my admitting I was wrong in
guessing a bad design, but apparently I wasn't clear enough.
This looks fine with my limited understanding of your project.

Regards,
Nikos

 

[Debra Farnham]

Hey Nikos!

You'll never believe how blonde I am.

I just reread your post that I responded to early early this morning.

Gosh I feel like an idiot.

Guess I now owe you for making you look at my silly post.

BTW - I did copy and paste.

I always design my tables and fields in a spreadsheet and print them out
prior to beginning design in Access.. *S*

Debra

 

[Nikos Yannacopoulos]

Debra,

You can't possibly be *that* blonde if you're using Access I also get
the wrong message sometimes and I'm not at all blonde, I assure you, so
it's got nothing to do with it anyway.
I'm relieved to hear you didn't actually type all that, and it's
definitely good practice to start your design on paper - which I never
do:-( I actually use this:

Sub Export_Table_Fields_List()
vName = Left(CurrentProject.Name, Len(CurrentProject.Name) - 4)
Open "c:\temp\" & vName & " Design.txt" For Output As #1
Print #1, "Table Design for Access Project:" & vbTab & CurrentDb.Name
For Each tbl In CurrentDb.TableDefs
If Left(tbl.Name, 4) <> "MSys" Then
Print #1,
Print #1, "Table:" & vbTab & tbl.Name
For Each fld In tbl.Fields
Print #1, fld.Type & vbTab & fld.Size & vbTab & fld.Name
Next
End If
Next
Close #1
End Sub

to save the basic design in a text file after I have put it together,
which comes handy sometimes when making changes during the development
phase. I also have another similar one for queries:

Sub Export_Query_Design()
vName = Left(CurrentProject.Name, Len(CurrentProject.Name) - 4)
Open "c:\temp\" & vName & " Query Design.txt" For Output As #1
Print #1, "Query Design for Access Project:" & vbTab & CurrentDb.Name
For Each qry In CurrentDb.QueryDefs
Print #1,
Print #1, "Query:" & vbTab & qry.Name
Print #1, qry.SQL
Next
Close #1
End Sub

which I use to check if a table or field is used in any query. You might
find use for it sometime.

Regards,
Nikos

 

[Guest]

I know I'll use it from time to time. Although I know I should, I don't
usually design on paper except maybe for a sketch or two when I'm getting
started, and I use Print Screen sometimes when I need to keep Relationships
in front of me or something like that.

 

[Nikos Yannacopoulos]

Hi Bruce!

Good to know (a) it may be useful to someone besides myself, and (b) I'm
not alone in breaching one of the basic rules!

Regards,
Nikos

 

[Debra Farnham]

Hi Nikos

I agree with Bruce on his response.. It does appear to be something quite
useful. Although, I will likely continue to design on paper first. I teach
the stuff and I suppose it's best to lead by example.

Sure wish someone could help with my initial problem though. I am still
seriously doubting the design.

Thanks again

Debra

 

[Nikos Yannacopoulos]

Debra,

I believe I speak for both Bruce and myself when I say neither of us
meant you should no longer design on paper; we do need a good example,
rare as it may be!

As for your original problem, I would love to help if I can, but it
would require me to understand the process you are modeling, which I
fear I am far from. Do you believe it's worth your time to try and put
it all down on "paper", while still not guaranteed to get any useful
feedback?

Regards,
Nikos

 

[Debra Farnham]

Nikos ... you make a very valid point.

I read a thread of 70+ articles about the very subject last night and have
decided to re-design. As most of the fields that would likely be nulls are
yes/no I decided to put all data from the one to one relationships into one
table.

I'm not happy about all the blank fields, but at least now it's easily
updateable, querying is less effort as is reporting.

Thanks again for taking the time to sift thru this.

Debra

 

[Nikos Yannacopoulos]

Now there's a brave girl! Actually you are setting one more good
example... I haven't seen people decide to redesign very often.

Good luck!

 

[Guest]

I will also stress that I am not suggesting you change your approach of
designing on paper. I will suggest that in future postings it would be
sufficient to describe just the essential fields in your tables, maybe
something like this (generic situation, not related to your database):

tblContacts
ContactID (primary key, or PK)
LastName, FirstName, etc.

tblAccounts
AccountID (PK)
ContactID (foreign key, or FK)
Date, etc.

A reader can assume that your contacts also have addresses, phone numbers,
and so forth, but it doesn't really affect the design. You can save yourself
some effort in posting, and somebody reading your post will have an easier
time sorting out the specific question. Also, some of your tables (such as
tblDistribution) do not seem to have a primary key, in which cases it is
especially helpful to identify foreign keys.
Good luck.