Invoicing database design

I am designing a database that includes the simple (!) functionality
of producing invoices (not an accounting package). I understand the
convention is to have a table for invoice headers and one for invoice
transactions. My question is what are the advantages of this approach
rather than just having one table for invoice transactions. The
printed invoice (an Access report) can have the invoice headings
(date, invoice no customer address etc) in the report header and the
invoice transactions in the report detail. What would be wrong with
that?

Gordon

"What would be wrong with that?"
Almost everything.
The common design of a header and transactions in separate but related
tables is always the correct way to accomplish this.

If you had one table to hold it all, how many individual transactions could
such a table hold? Well, with a limit of 256 fields in a table, you will
run out very quickly. And if you are saying to repeat the header info for
each transaction, then you are breaking the redundant data rule.

And in the report, where will the header info come from?

Or maybe I am missing the point and this post is a joke.
wrote in message
...
I am designing a database that includes the simple (!) functionality
of producing invoices (not an accounting package). I understand the
convention is to have a table for invoice headers and one for invoice
transactions. My question is what are the advantages of this approach
rather than just having one table for invoice transactions. The
printed invoice (an Access report) can have the invoice headings
(date, invoice no customer address etc) in the report header and the
invoice transactions in the report detail. What would be wrong with
that?

Gordon

On 4 Nov, 14:21, "Klatuu" wrote:
"What would be wrong with that?"
Almost everything.
The common design of a header and transactions in separate but related
tables is always the correct way to accomplish this.

If you had one table to hold it all, how many individual transactions could
such a table hold? *Well, with a limit of 256 fields in a table, you will
run out very quickly. *And if you are saying to repeat the header info for
each transaction, then you are breaking the redundant data rule.

And in the report, where will the header info come from?

Or maybe I am missing the point and this post is a wrote in message

...



I am designing a database that includes the simple (!) *functionality
of *producing invoices (not an accounting package). *I understand the
convention is to have a table for invoice headers and one for invoice
transactions. *My question is what are the advantages of this approach
rather than just having one table for invoice transactions. *The
printed invoice (an Access report) can have the invoice headings
(date, invoice no customer address etc) in the report header and the
invoice transactions in the report detail. *What would be wrong with
that?

Gordon- Hide quoted text -

- Show quoted text -

Wow, I feel as though I have been flamed. This is no joke. It was
only a question on which I wanted advice. I said the invoicing
function was simple, not the database itself.

Fields in the one table invoicing transactions I envisage would be:

invoice date
invoice no
customerID
transaction date
transaction ref
productID
item description
Quantity
Unit price

As I see it, only the first 3 would break the redundant data rule.
The data for the invoice report (including the header) would be built
on the fly (using VBA) at time of invoice creation, drawing data not
just from the invoice transaction table but also the related tables on
customers/products etc.

But thanks for responding - at least you confirmed the only objection
to a one table design for invoice transactions is the data redundancy
rule which in this particular case is not a great overhead if it saves
having to maintain and update 2 tables.

Had I been asked I would have recommended against adding the last sentence to
the previous posting, but the other points are valid. My understanding of
your proposed structure is different from Klatuu's, but in either case there
are literally no arguments in favor of your approach in a relational database.
It would make sense only in a flat database such as Excel. When a flat
database is called for Excel is generally the better tool for the job, but a
flat databse is not called for here.

Are you planning to copy the invoice number and other invoice header
information to each invoice item record? If so, is the only reason that you
believe it would be less overhead than maintaining two separate tables?

There are any number of objections to such an approach, one of which is that
overhead is likely to be greater, not less. You would not throw all of your
paper files into a large crate in the belief that a single container is less
overhead than a series of file drawers. The analogy is imprecise, but still
relevant.

Among the problems I see is that you do not have a ready way to view a single
invoice's information. One way would be to scroll through all of the records
until you notice the number you want, then take note of when the number
changes as you continue to scroll through the records. Another way would be
to filter the recordset (or load a selective recordset) to view a single
invoice. With a filtered recordset you would need to run the filter again to
view the next batch of records. With invoice header information in a single
table you could simply navigate to the next invoice to see all of that
invoice's associated line items. The flat file approach will inevitably lead
to a more awkward user interface.

Another objection would be the possibility of data entry errors. You could
avoid that to some extent by using code to copy the record, but that involves
overhead. Another is that you cannot enforce unique invoice numbers at the
table level. You could use code to check whether an invoice number has been
used for a different customer on a different date or something, but again
that is a lot of overhead, and probably difficult to construct.

"Only" three fields breaking the redundant data rule is three more than I
would accept. There is sometimes room for debate about what constitutes
redundant data, but not in this case. Adding a related table is easy, and
does not involve "maintenance" after it is created. Coding for a flat
structure is where the overhead really starts to add up.

wrote:
"What would be wrong with that?"
Almost everything.
[quoted text clipped - 25 lines]

- Show quoted text -

Wow, I feel as though I have been flamed. This is no joke. It was
only a question on which I wanted advice. I said the invoicing
function was simple, not the database itself.

Fields in the one table invoicing transactions I envisage would be:

invoice date
invoice no
customerID
transaction date
transaction ref
productID
item description
Quantity
Unit price

As I see it, only the first 3 would break the redundant data rule.
The data for the invoice report (including the header) would be built
on the fly (using VBA) at time of invoice creation, drawing data not
just from the invoice transaction table but also the related tables on
customers/products etc.

But thanks for responding - at least you confirmed the only objection
to a one table design for invoice transactions is the data redundancy
rule which in this particular case is not a great overhead if it saves
having to maintain and update 2 tables.

--
Message posted via http://www.accessmonster.com

On 4 Nov, 16:01, "BruceM via AccessMonster.com" u54429@uwe wrote:
Had I been asked I would have recommended against adding the last sentence to
the previous posting, but the other points are valid. *My understanding of
your proposed structure is different from Klatuu's, but in either case there
are literally no arguments in favor of your approach in a relational database.
It would make sense only in a flat database such as Excel. *When a flat
database is called for Excel is generally the better tool for the job, but a
flat databse is not called for here.

Are you planning to copy the invoice number and other invoice header
information to each invoice item record? *If so, is the only reason that you
believe it would be less overhead than maintaining two separate tables?

There are any number of objections to such an approach, one of which is that
overhead is likely to be greater, not less. *You would not throw all of your
paper files into a large crate in the belief that a single container is less
overhead than a series of file drawers. *The analogy is imprecise, but still
relevant.

Among the problems I see is that you do not have a ready way to view a single
invoice's information. *One way would be to scroll through all of the records
until you notice the number you want, then take note of when the number
changes as you continue to scroll through the records. *Another way would be
to filter the recordset (or load a selective recordset) to view a single
invoice. *With a filtered recordset you would need to run the filter again to
view the next batch of records. With invoice header information in a single
table you could simply navigate to the next invoice to see all of that
invoice's associated line items. *The flat file approach will inevitably lead
to a more awkward user interface.

Another objection would be the possibility of data entry errors. *You could
avoid that to some extent by using code to copy the record, but that involves
overhead. *Another is that you cannot enforce unique invoice numbers at the
table level. *You could use code to check whether an invoice number has been
used for a different customer on a different date or something, but again
that is a lot of overhead, and probably difficult to construct.

"Only" three fields breaking the redundant data rule is three more than I
would accept. *There is sometimes room for debate about what constitutes
redundant data, but not in this case. *Adding a related table is easy, and
does not involve "maintenance" after it is created. *Coding for a flat
structure is where the overhead really starts to add up.





wrote:
"What would be wrong with that?"
Almost everything.
[quoted text clipped - 25 lines]

- Show quoted text -

Wow, I feel as though I have been flamed. *This is no joke. It was
only a question on which I wanted advice. I said the invoicing
function was simple, not the database itself.

Fields in the one table invoicing transactions I envisage would be:

invoice date
invoice no
customerID
transaction date
transaction ref
productID
item description
Quantity
Unit price

As I see it, only the first 3 would break the redundant data rule.
The data for the invoice report (including the header) would be built
on the fly (using VBA) at time of invoice creation, drawing data not
just from the invoice transaction table but also the related tables on
customers/products etc.

But thanks for responding - at least you confirmed the only objection
to a one table design for invoice transactions is the data redundancy
rule which in this particular case is not a great overhead if it saves
having to maintain and update 2 tables.

--
Message posted viahttp://www.accessmonster.com- Hide quoted text -

- Show quoted text -

Hi Bruce, Thanks for your detailed post. You make a much more
convincing argument which has won me over. Part of my reticence to
construct an invoice header table and a separate one for invoice item
lines lay in my ignorance of the approach I should take. I did say I
was not designing an accounting system here but just the ability to
print invoices. Can you give me some advice?
I understand what fields should be in the 2 tables but am unclear how
to populate them.

The nature of the business is a service based one - charges are made
to a range of clients for each enquiry handled. These are captured
through a basic data entry screen, allocated to a client and populate
an enquiries transaction table. What is the best approach then to
populate the invoice header and invoice lines tables?

Gordon

Generally you would have something like the following:

tblInvoice (Invoice header table)
InvoiceID (primary key, or PK)
CustomerID
InvoiceDate
InitiatedBy
Other information specific to the invoice

tblDetails (line items or details for the invoice)
DetailID (PK)
InvoiceID
Item
UnitPrice
Quantity

InvoiceID needs to be the same data type (Number, Text) in both tables. If
InvoiceID is an autonumber in tblInvoice, it needs to be Number (Long Integer)
in tblDetails. Note that Number can be of various types. Long Integer,
Double, and Currency are the ones used most of the time.

Go to View Relationships. Add both tables. Drag InvoiceID from one table
to InvoiceID on the other. Click Enforce Referential Integrity when the
dialog appears. Note that the fields do not need to be the same name, but it
may be easier to keep track of that way.

Create a main form based on tblInvoice. From the toolbox, add a
subform/subreport control, just as you would add a text box, line, or anthing
else. With the subform control selected, click View Properties. Set its
Source Object to tblDetails, and its Link Child and Link Master fields to
InvoiceID if it is not already done. Click the three dots next to either
Link property, and it should take you through the rest of the process.

Add an Invoice record on the main form. On the subform, add a few line items
(details). Create another Invoice record (main form) with a few line items.
Go back to the first record. The line items should still be there. Look at
the tables. Each Detail record should have a value in InvoiceID
corresponding to an InvoiceID value in tblInvoice.

In many cases there is a listing of items that may be added to Details. If
you were dealing in products it would be a Products table. In the case of
services there may be a listing of services and prices. In this case you
would have a Services table:

tblService
ServiceID (PK
Description
UnitPrice
Quantity

tblDetails would look like this:

tblDetails (line items or details for the invoice)
DetailID (PK)
InvoiceID
ServiceID
UnitPrice
Quantity

Add tblService to the Relationship window, and create a relationship between
the ServiceID fields.

Base the subform on tblDetails as before. Rather than Item you will be
linking to tblService. Make a combo box. Set its Row Source to a query
based on tblService. The first column (hidden) in the combo box is ServiceID.
The other column(s) are visible, allowing you to select the item by name
rather than number. Set the combo box Control Source to ServiceID.

This is just a sketch, but I will have to leave it at that for now. For more
information about design and general database principles, this is a list John
Vinson often provides:

Jeff Conrad's resources page:
http://www.accessmvp.com/JConrad/acc...resources.html

The Access Web resources page:
http://www.mvps.org/access/resources/index.html

Roger Carlson's tutorials, samples and tips:
http://www.rogersaccesslibrary.com/

A free tutorial written by Crystal:
http://allenbrowne.com/casu-22.html

A video how-to series by Crystal:
http://www.YouTube.com/user/LearnAccessByCrystal

MVP Allen Browne's tutorials:
http://allenbrowne.com/links.html#Tutorials

Crystal's tutorial is as good a place as any to start, IMHO.

To set up an incrementing Invoice number, one technique may be found he
http://www.rogersaccesslibrary.com/f...ts.asp?TID=395


wrote:
Had I been asked I would have recommended against adding the last sentence to
the previous posting, but the other points are valid. Â*My understanding of
[quoted text clipped - 76 lines]

- Show quoted text -

Hi Bruce, Thanks for your detailed post. You make a much more
convincing argument which has won me over. Part of my reticence to
construct an invoice header table and a separate one for invoice item
lines lay in my ignorance of the approach I should take. I did say I
was not designing an accounting system here but just the ability to
print invoices. Can you give me some advice?
I understand what fields should be in the 2 tables but am unclear how
to populate them.

The nature of the business is a service based one - charges are made
to a range of clients for each enquiry handled. These are captured
through a basic data entry screen, allocated to a client and populate
an enquiries transaction table. What is the best approach then to
populate the invoice header and invoice lines tables?

Gordon

--
Message posted via AccessMonster.com
http://www.accessmonster.com/Uwe/For...esign/200911/1