strategy for data entry in multiple tables

A great strength of Access is the ability to base a form on a multi-table
query and use the form for data entry. However, there are some important
issues. Let us assume a simple database with two master tables and a
junction table. One master table (subjects) has a primary key that is a text
variable. The other master table is an event table with an autonumbered
EventID as primary key. Assume for this example that tblEventID has fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has all fields
from all 3 tables? For this to occur, code or macro must be written to run
after the SubjectID is entered in the SubjectID field from tblSubjecst, to
determine if a new record should be written in the subjects table. If a new
record does not need to be made, then the SubjectsID field should be cleared,
but the SubjectsID value placed in the SubjectsID field from tblJunction.

Issue 2. A bigger problem occurs when data are entered for tblEvent on the
single bound entry form. Code or macro must be written to determine if the
non-primary key fields are already present in tblEvents. If they are, then
the EventID from the matching record should be copied into EventID field on
the data entry form for tblEvents. If not, then a new record must be written
into tblEvent and the autonumber copied into the data transfer form.

The big question is: should there be separate data entry forms for the two
master tables, possibly on unbound forms that pass appropriate values to the
relevant data entry forms, or to an error event? The tblJunction data entry
form would start out with the passed values in the foreign key fields. Is
there a better strategy for dealing data entry with referential integrity and
cascade updating.

LAF

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a multi-table
query and use the form for data entry. However, there are some important
issues. Let us assume a simple database with two master tables and a
junction table. One master table (subjects) has a primary key that is a
text
variable. The other master table is an event table with an autonumbered
EventID as primary key. Assume for this example that tblEventID has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has all
fields
from all 3 tables? For this to occur, code or macro must be written to
run
after the SubjectID is entered in the SubjectID field from tblSubjecst, to
determine if a new record should be written in the subjects table. If a
new
record does not need to be made, then the SubjectsID field should be
cleared,
but the SubjectsID value placed in the SubjectsID field from tblJunction.

Maybe? What is the relationship between Subject and Event? If 1 to 1, ok.
But otherwise, it seems to me subject and event should be separate forms
with data from the junction table in a subform (if it makes sense to show
the related data in both places). You seem to be concerned about duplicate
data in subject. Ok, so, do some validation before update/insert for
subject records....and if there is a duplicate, cancel the update and go to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for tblEvent on
the
single bound entry form. Code or macro must be written to determine if
the
non-primary key fields are already present in tblEvents. If they are,
then
the EventID from the matching record should be copied into EventID field
on
the data entry form for tblEvents. If not, then a new record must be
written
into tblEvent and the autonumber copied into the data transfer form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms for the
two
master tables, possibly on unbound forms that pass appropriate values to
the
relevant data entry forms, or to an error event? The tblJunction data
entry
form would start out with the passed values in the foreign key fields. Is
there a better strategy for dealing data entry with referential integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound or
unbound, you're going to need to do validation to ensure that any new record
is not a duplicate of an existing record. I'm not sure why you'd have the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key for either
subject or event would be passed automatically.


LAF

Hi Paul,

Thanks for the advice. Let us assume that there is one to many relationship
between a master table and the junction table, for each master table. There
is not necessarily one to one between the two master tables.

In principle then, it appears that the best strategy is to combine data
entry and validation for each master table separately, and then to copy the
primary field to the data entry form for the junction table. I assume that
there would be no problem with referential integrity to have a new record in
a master field with no foreign key, yet, put in a new record in the junction
table. Is this correct?

Thanks,

LAF

"Paul Overway" wrote:

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a multi-table
query and use the form for data entry. However, there are some important
issues. Let us assume a simple database with two master tables and a
junction table. One master table (subjects) has a primary key that is a
text
variable. The other master table is an event table with an autonumbered
EventID as primary key. Assume for this example that tblEventID has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has all
fields
from all 3 tables? For this to occur, code or macro must be written to
run
after the SubjectID is entered in the SubjectID field from tblSubjecst, to
determine if a new record should be written in the subjects table. If a
new
record does not need to be made, then the SubjectsID field should be
cleared,
but the SubjectsID value placed in the SubjectsID field from tblJunction.

Maybe? What is the relationship between Subject and Event? If 1 to 1, ok.
But otherwise, it seems to me subject and event should be separate forms
with data from the junction table in a subform (if it makes sense to show
the related data in both places). You seem to be concerned about duplicate
data in subject. Ok, so, do some validation before update/insert for
subject records....and if there is a duplicate, cancel the update and go to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for tblEvent on
the
single bound entry form. Code or macro must be written to determine if
the
non-primary key fields are already present in tblEvents. If they are,
then
the EventID from the matching record should be copied into EventID field
on
the data entry form for tblEvents. If not, then a new record must be
written
into tblEvent and the autonumber copied into the data transfer form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms for the
two
master tables, possibly on unbound forms that pass appropriate values to
the
relevant data entry forms, or to an error event? The tblJunction data
entry
form would start out with the passed values in the foreign key fields. Is
there a better strategy for dealing data entry with referential integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound or
unbound, you're going to need to do validation to ensure that any new record
is not a duplicate of an existing record. I'm not sure why you'd have the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key for either
subject or event would be passed automatically.


LAF

My experience (admittedly limited) with junction tables has been that one of
the main tables is relatively static (such as a Student table) and the other
is more dynamic (such as a Courses table). Each student can be in many
courses, and each course can have many students, so a junction table resolves
the many-to-many relationship. A form could be based on the Courses table
(or a query based on the table), with a subform based on the junction table
to list the students taking that particular course. The subform could have a
combo box that has as its row source a query based on the Student table. The
bound column would be the one containing the primary key. A Not In List
event could open a form to add a record to the Student table, if need be.
I don't know if this approach would work in your case. My point is just
that the tables can all work together without being combined into a single
query, and that combining them is not necessarily an advantage. You wrote
"Let us assume that there is one to many relationship between a master table
and the junction table, for each master table." That is generally the case
with a junction table. It's what a junction table does.
I don't really follow the purpose of your database, but it each subject can
be associated with many events, and each event with many subjects, then you
have many-to-many, and need a junction table. The junction table needs to
contain fields that correspond to the primary keys from the main tables.
These foreign keys are established when you set up the relationships between
the tables. You don't typically enter data directly into the foreign key
fields. In the example I gave, each record in the subform's record source
contains as its foreign key the primary key field from the parent form's
record source.
I agree with what Paul said, and would tend to agree that a subform is often
the most workable choice. Perhaps if you have more questions you could be
more specific about what the database does, or at least use an analogous
situation as an example. If you were talking about Customers and Orders, or
Students and Courses the relationship would be pretty clear, but the
connection between Subject and Event is not immediately apparent, at least
not this early in the morning.

"LAF" wrote:

Hi Paul,

Thanks for the advice. Let us assume that there is one to many relationship
between a master table and the junction table, for each master table. There
is not necessarily one to one between the two master tables.

In principle then, it appears that the best strategy is to combine data
entry and validation for each master table separately, and then to copy the
primary field to the data entry form for the junction table. I assume that
there would be no problem with referential integrity to have a new record in
a master field with no foreign key, yet, put in a new record in the junction
table. Is this correct?

Thanks,

LAF

"Paul Overway" wrote:

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a multi-table
query and use the form for data entry. However, there are some important
issues. Let us assume a simple database with two master tables and a
junction table. One master table (subjects) has a primary key that is a
text
variable. The other master table is an event table with an autonumbered
EventID as primary key. Assume for this example that tblEventID has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has all
fields
from all 3 tables? For this to occur, code or macro must be written to
run
after the SubjectID is entered in the SubjectID field from tblSubjecst, to
determine if a new record should be written in the subjects table. If a
new
record does not need to be made, then the SubjectsID field should be
cleared,
but the SubjectsID value placed in the SubjectsID field from tblJunction.

Maybe? What is the relationship between Subject and Event? If 1 to 1, ok.
But otherwise, it seems to me subject and event should be separate forms
with data from the junction table in a subform (if it makes sense to show
the related data in both places). You seem to be concerned about duplicate
data in subject. Ok, so, do some validation before update/insert for
subject records....and if there is a duplicate, cancel the update and go to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for tblEvent on
the
single bound entry form. Code or macro must be written to determine if
the
non-primary key fields are already present in tblEvents. If they are,
then
the EventID from the matching record should be copied into EventID field
on
the data entry form for tblEvents. If not, then a new record must be
written
into tblEvent and the autonumber copied into the data transfer form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms for the
two
master tables, possibly on unbound forms that pass appropriate values to
the
relevant data entry forms, or to an error event? The tblJunction data
entry
form would start out with the passed values in the foreign key fields. Is
there a better strategy for dealing data entry with referential integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound or
unbound, you're going to need to do validation to ensure that any new record
is not a duplicate of an existing record. I'm not sure why you'd have the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key for either
subject or event would be passed automatically.


LAF

I think you're misusing or misinstanding keys. You should have a PK in
Event, another PK in Subject, and 2 FK (EventID and SubjectID) in the
junction. You shouldn't be putting an FK in either of the master tables.
Example

Event
1 Gala
2 Dinner

Subject
1 Funding
2 Purpose

Junction
Event Subject
1 1
1 2
2 2

In the example above, I've omitted one of the possible combinations.
Nevertheless, we can see for the Gala the subject will be Funding and
Purpose, whereas for the Dinner the only subject will be purpose. If you
have a subform for Junction on the Event form and on the Subject form, you
can see what subjects will be discussed at the event or at what event the
subject will be discussed.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hi Paul,

Thanks for the advice. Let us assume that there is one to many
relationship
between a master table and the junction table, for each master table.
There
is not necessarily one to one between the two master tables.

In principle then, it appears that the best strategy is to combine data
entry and validation for each master table separately, and then to copy
the
primary field to the data entry form for the junction table. I assume
that
there would be no problem with referential integrity to have a new record
in
a master field with no foreign key, yet, put in a new record in the
junction
table. Is this correct?

Thanks,

LAF

"Paul Overway" wrote:

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a
multi-table
query and use the form for data entry. However, there are some
important
issues. Let us assume a simple database with two master tables and a
junction table. One master table (subjects) has a primary key that is
a
text
variable. The other master table is an event table with an
autonumbered
EventID as primary key. Assume for this example that tblEventID has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has all
fields
from all 3 tables? For this to occur, code or macro must be written to
run
after the SubjectID is entered in the SubjectID field from tblSubjecst,
to
determine if a new record should be written in the subjects table. If
a
new
record does not need to be made, then the SubjectsID field should be
cleared,
but the SubjectsID value placed in the SubjectsID field from
tblJunction.

Maybe? What is the relationship between Subject and Event? If 1 to 1,
ok.
But otherwise, it seems to me subject and event should be separate forms
with data from the junction table in a subform (if it makes sense to show
the related data in both places). You seem to be concerned about
duplicate
data in subject. Ok, so, do some validation before update/insert for
subject records....and if there is a duplicate, cancel the update and go
to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for tblEvent on
the
single bound entry form. Code or macro must be written to determine if
the
non-primary key fields are already present in tblEvents. If they are,
then
the EventID from the matching record should be copied into EventID
field
on
the data entry form for tblEvents. If not, then a new record must be
written
into tblEvent and the autonumber copied into the data transfer form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms for the
two
master tables, possibly on unbound forms that pass appropriate values
to
the
relevant data entry forms, or to an error event? The tblJunction data
entry
form would start out with the passed values in the foreign key fields.
Is
there a better strategy for dealing data entry with referential
integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound or
unbound, you're going to need to do validation to ensure that any new
record
is not a duplicate of an existing record. I'm not sure why you'd have
the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key for
either
subject or event would be passed automatically.


LAF

Hello All,

Thanks for the stimulating discussion. Let me go back to the original
problem. The data entry form is not to look at records, it is for entering
(and validating) data. I don't see how a subform for the junction table can
be used appropriately with a form for just one of the master tables. The
foreign key for the other master table will be present, but the data entry
needs to go into the primary key of the other master table.

By the way, the database I am developing is for capturing birds in mist
nets. We put numbered aluminum bands on the legs of birds we capture.
tblBirds lists each individual by band number (=BirdID) as the primary key,
with other fields such as species, leftleg, rightleg (for those birds on
which we place color bands as well). tblEvents lists each capture event by
site, date, and time. The EventID is an autonumbered field that is based on
unique combinations of site, date, and time. The junction table deals with
the many to many relationship between BirdID and EventID. The junction table
has many fields that deal with data collected on birds captured in nets, and
is in one to one relationship with tables with specialized data on particular
birds. This is where I see a subform for data entry being useful.

If both master tables could be used in the same data entry form, then
subforms would be feasible for the junction table. Is it possible for two
tables to be in the same form, each with their own primary keys, and then to
use the junction table as a subform?

Thanks,

LAF

"Paul Overway" wrote:

I think you're misusing or misinstanding keys. You should have a PK in
Event, another PK in Subject, and 2 FK (EventID and SubjectID) in the
junction. You shouldn't be putting an FK in either of the master tables.
Example

Event
1 Gala
2 Dinner

Subject
1 Funding
2 Purpose

Junction
Event Subject
1 1
1 2
2 2

In the example above, I've omitted one of the possible combinations.
Nevertheless, we can see for the Gala the subject will be Funding and
Purpose, whereas for the Dinner the only subject will be purpose. If you
have a subform for Junction on the Event form and on the Subject form, you
can see what subjects will be discussed at the event or at what event the
subject will be discussed.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hi Paul,

Thanks for the advice. Let us assume that there is one to many
relationship
between a master table and the junction table, for each master table.
There
is not necessarily one to one between the two master tables.

In principle then, it appears that the best strategy is to combine data
entry and validation for each master table separately, and then to copy
the
primary field to the data entry form for the junction table. I assume
that
there would be no problem with referential integrity to have a new record
in
a master field with no foreign key, yet, put in a new record in the
junction
table. Is this correct?

Thanks,

LAF

"Paul Overway" wrote:

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a
multi-table
query and use the form for data entry. However, there are some
important
issues. Let us assume a simple database with two master tables and a
junction table. One master table (subjects) has a primary key that is
a
text
variable. The other master table is an event table with an
autonumbered
EventID as primary key. Assume for this example that tblEventID has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has all
fields
from all 3 tables? For this to occur, code or macro must be written to
run
after the SubjectID is entered in the SubjectID field from tblSubjecst,
to
determine if a new record should be written in the subjects table. If
a
new
record does not need to be made, then the SubjectsID field should be
cleared,
but the SubjectsID value placed in the SubjectsID field from
tblJunction.

Maybe? What is the relationship between Subject and Event? If 1 to 1,
ok.
But otherwise, it seems to me subject and event should be separate forms
with data from the junction table in a subform (if it makes sense to show
the related data in both places). You seem to be concerned about
duplicate
data in subject. Ok, so, do some validation before update/insert for
subject records....and if there is a duplicate, cancel the update and go
to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for tblEvent on
the
single bound entry form. Code or macro must be written to determine if
the
non-primary key fields are already present in tblEvents. If they are,
then
the EventID from the matching record should be copied into EventID
field
on
the data entry form for tblEvents. If not, then a new record must be
written
into tblEvent and the autonumber copied into the data transfer form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms for the
two
master tables, possibly on unbound forms that pass appropriate values
to
the
relevant data entry forms, or to an error event? The tblJunction data
entry
form would start out with the passed values in the foreign key fields.
Is
there a better strategy for dealing data entry with referential
integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound or
unbound, you're going to need to do validation to ensure that any new
record
is not a duplicate of an existing record. I'm not sure why you'd have
the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key for
either
subject or event would be passed automatically.


LAF

Ah...ok. I see what you're trying to do now.

I'd have a single unbound entry form for this, with 2 listboxs...one for
Birds, and another for Events. I'd have an Add button that would add a
record to a subform for the Junction data. I'd use the selections from the
2 listboxes in the link master/link child property for the subform, which
would allow you to see how the 2 master tables are related and the junction
data for that combination.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hello All,

Thanks for the stimulating discussion. Let me go back to the original
problem. The data entry form is not to look at records, it is for
entering
(and validating) data. I don't see how a subform for the junction table
can
be used appropriately with a form for just one of the master tables. The
foreign key for the other master table will be present, but the data entry
needs to go into the primary key of the other master table.

By the way, the database I am developing is for capturing birds in mist
nets. We put numbered aluminum bands on the legs of birds we capture.
tblBirds lists each individual by band number (=BirdID) as the primary
key,
with other fields such as species, leftleg, rightleg (for those birds on
which we place color bands as well). tblEvents lists each capture event
by
site, date, and time. The EventID is an autonumbered field that is based
on
unique combinations of site, date, and time. The junction table deals
with
the many to many relationship between BirdID and EventID. The junction
table
has many fields that deal with data collected on birds captured in nets,
and
is in one to one relationship with tables with specialized data on
particular
birds. This is where I see a subform for data entry being useful.

If both master tables could be used in the same data entry form, then
subforms would be feasible for the junction table. Is it possible for two
tables to be in the same form, each with their own primary keys, and then
to
use the junction table as a subform?

Thanks,

LAF

"Paul Overway" wrote:

I think you're misusing or misinstanding keys. You should have a PK in
Event, another PK in Subject, and 2 FK (EventID and SubjectID) in the
junction. You shouldn't be putting an FK in either of the master tables.
Example

Event
1 Gala
2 Dinner

Subject
1 Funding
2 Purpose

Junction
Event Subject
1 1
1 2
2 2

In the example above, I've omitted one of the possible combinations.
Nevertheless, we can see for the Gala the subject will be Funding and
Purpose, whereas for the Dinner the only subject will be purpose. If you
have a subform for Junction on the Event form and on the Subject form,
you
can see what subjects will be discussed at the event or at what event the
subject will be discussed.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hi Paul,

Thanks for the advice. Let us assume that there is one to many
relationship
between a master table and the junction table, for each master table.
There
is not necessarily one to one between the two master tables.

In principle then, it appears that the best strategy is to combine data
entry and validation for each master table separately, and then to copy
the
primary field to the data entry form for the junction table. I assume
that
there would be no problem with referential integrity to have a new
record
in
a master field with no foreign key, yet, put in a new record in the
junction
table. Is this correct?

Thanks,

LAF

"Paul Overway" wrote:

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a
multi-table
query and use the form for data entry. However, there are some
important
issues. Let us assume a simple database with two master tables and
a
junction table. One master table (subjects) has a primary key that
is
a
text
variable. The other master table is an event table with an
autonumbered
EventID as primary key. Assume for this example that tblEventID has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has
all
fields
from all 3 tables? For this to occur, code or macro must be written
to
run
after the SubjectID is entered in the SubjectID field from
tblSubjecst,
to
determine if a new record should be written in the subjects table.
If
a
new
record does not need to be made, then the SubjectsID field should be
cleared,
but the SubjectsID value placed in the SubjectsID field from
tblJunction.

Maybe? What is the relationship between Subject and Event? If 1 to
1,
ok.
But otherwise, it seems to me subject and event should be separate
forms
with data from the junction table in a subform (if it makes sense to
show
the related data in both places). You seem to be concerned about
duplicate
data in subject. Ok, so, do some validation before update/insert for
subject records....and if there is a duplicate, cancel the update and
go
to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for tblEvent
on
the
single bound entry form. Code or macro must be written to determine
if
the
non-primary key fields are already present in tblEvents. If they
are,
then
the EventID from the matching record should be copied into EventID
field
on
the data entry form for tblEvents. If not, then a new record must
be
written
into tblEvent and the autonumber copied into the data transfer form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms for
the
two
master tables, possibly on unbound forms that pass appropriate
values
to
the
relevant data entry forms, or to an error event? The tblJunction
data
entry
form would start out with the passed values in the foreign key
fields.
Is
there a better strategy for dealing data entry with referential
integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound or
unbound, you're going to need to do validation to ensure that any new
record
is not a duplicate of an existing record. I'm not sure why you'd have
the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key for
either
subject or event would be passed automatically.


LAF

Interesting discussion, but it leaves me wondering how tblEvents and tblBirds
are related many-to-many unless an individual bird could be captured several
times. I see how each event could involve many birds, but not the other way
around. What relationship is the junction table resolving? I would have
imagined based on my understanding of the question that it would be Events
Birds Bird Details in a cascading one-to-many relationship, with nested
subforms. I don't really need an answer, but I am a bit curious as to how
this discussion will unfold.

"Paul Overway" wrote:

Ah...ok. I see what you're trying to do now.

I'd have a single unbound entry form for this, with 2 listboxs...one for
Birds, and another for Events. I'd have an Add button that would add a
record to a subform for the Junction data. I'd use the selections from the
2 listboxes in the link master/link child property for the subform, which
would allow you to see how the 2 master tables are related and the junction
data for that combination.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hello All,

Thanks for the stimulating discussion. Let me go back to the original
problem. The data entry form is not to look at records, it is for
entering
(and validating) data. I don't see how a subform for the junction table
can
be used appropriately with a form for just one of the master tables. The
foreign key for the other master table will be present, but the data entry
needs to go into the primary key of the other master table.

By the way, the database I am developing is for capturing birds in mist
nets. We put numbered aluminum bands on the legs of birds we capture.
tblBirds lists each individual by band number (=BirdID) as the primary
key,
with other fields such as species, leftleg, rightleg (for those birds on
which we place color bands as well). tblEvents lists each capture event
by
site, date, and time. The EventID is an autonumbered field that is based
on
unique combinations of site, date, and time. The junction table deals
with
the many to many relationship between BirdID and EventID. The junction
table
has many fields that deal with data collected on birds captured in nets,
and
is in one to one relationship with tables with specialized data on
particular
birds. This is where I see a subform for data entry being useful.

If both master tables could be used in the same data entry form, then
subforms would be feasible for the junction table. Is it possible for two
tables to be in the same form, each with their own primary keys, and then
to
use the junction table as a subform?

Thanks,

LAF

"Paul Overway" wrote:

I think you're misusing or misinstanding keys. You should have a PK in
Event, another PK in Subject, and 2 FK (EventID and SubjectID) in the
junction. You shouldn't be putting an FK in either of the master tables.
Example

Event
1 Gala
2 Dinner

Subject
1 Funding
2 Purpose

Junction
Event Subject
1 1
1 2
2 2

In the example above, I've omitted one of the possible combinations.
Nevertheless, we can see for the Gala the subject will be Funding and
Purpose, whereas for the Dinner the only subject will be purpose. If you
have a subform for Junction on the Event form and on the Subject form,
you
can see what subjects will be discussed at the event or at what event the
subject will be discussed.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hi Paul,

Thanks for the advice. Let us assume that there is one to many
relationship
between a master table and the junction table, for each master table.
There
is not necessarily one to one between the two master tables.

In principle then, it appears that the best strategy is to combine data
entry and validation for each master table separately, and then to copy
the
primary field to the data entry form for the junction table. I assume
that
there would be no problem with referential integrity to have a new
record
in
a master field with no foreign key, yet, put in a new record in the
junction
table. Is this correct?

Thanks,

LAF

"Paul Overway" wrote:

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a
multi-table
query and use the form for data entry. However, there are some
important
issues. Let us assume a simple database with two master tables and
a
junction table. One master table (subjects) has a primary key that
is
a
text
variable. The other master table is an event table with an
autonumbered
EventID as primary key. Assume for this example that tblEventID has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has
all
fields
from all 3 tables? For this to occur, code or macro must be written
to
run
after the SubjectID is entered in the SubjectID field from
tblSubjecst,
to
determine if a new record should be written in the subjects table.
If
a
new
record does not need to be made, then the SubjectsID field should be
cleared,
but the SubjectsID value placed in the SubjectsID field from
tblJunction.

Maybe? What is the relationship between Subject and Event? If 1 to
1,
ok.
But otherwise, it seems to me subject and event should be separate
forms
with data from the junction table in a subform (if it makes sense to
show
the related data in both places). You seem to be concerned about
duplicate
data in subject. Ok, so, do some validation before update/insert for
subject records....and if there is a duplicate, cancel the update and
go
to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for tblEvent
on
the
single bound entry form. Code or macro must be written to determine
if
the
non-primary key fields are already present in tblEvents. If they
are,
then
the EventID from the matching record should be copied into EventID
field
on
the data entry form for tblEvents. If not, then a new record must
be
written
into tblEvent and the autonumber copied into the data transfer form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms for
the
two
master tables, possibly on unbound forms that pass appropriate
values
to
the
relevant data entry forms, or to an error event? The tblJunction
data
entry
form would start out with the passed values in the foreign key
fields.
Is
there a better strategy for dealing data entry with referential
integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound or
unbound, you're going to need to do validation to ensure that any new
record
is not a duplicate of an existing record. I'm not sure why you'd have
the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key for
either
subject or event would be passed automatically.


LAF

It makes sense because birds are being captured collectively as a group in
nets. If they were being captured individually, the junction would be
unnecessary....a bird would be related to events in a one to many. But
because the birds are captured collectively, the junction is used to resolve
what birds were captured during an event and vice versa.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"BruceM" wrote in message
...
Interesting discussion, but it leaves me wondering how tblEvents and
tblBirds
are related many-to-many unless an individual bird could be captured
several
times. I see how each event could involve many birds, but not the other
way
around. What relationship is the junction table resolving? I would have
imagined based on my understanding of the question that it would be Events

Birds Bird Details in a cascading one-to-many relationship, with nested
subforms. I don't really need an answer, but I am a bit curious as to how
this discussion will unfold.

"Paul Overway" wrote:

Ah...ok. I see what you're trying to do now.

I'd have a single unbound entry form for this, with 2 listboxs...one for
Birds, and another for Events. I'd have an Add button that would add a
record to a subform for the Junction data. I'd use the selections from
the
2 listboxes in the link master/link child property for the subform, which
would allow you to see how the 2 master tables are related and the
junction
data for that combination.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hello All,

Thanks for the stimulating discussion. Let me go back to the original
problem. The data entry form is not to look at records, it is for
entering
(and validating) data. I don't see how a subform for the junction
table
can
be used appropriately with a form for just one of the master tables.
The
foreign key for the other master table will be present, but the data
entry
needs to go into the primary key of the other master table.

By the way, the database I am developing is for capturing birds in mist
nets. We put numbered aluminum bands on the legs of birds we capture.
tblBirds lists each individual by band number (=BirdID) as the primary
key,
with other fields such as species, leftleg, rightleg (for those birds
on
which we place color bands as well). tblEvents lists each capture
event
by
site, date, and time. The EventID is an autonumbered field that is
based
on
unique combinations of site, date, and time. The junction table deals
with
the many to many relationship between BirdID and EventID. The junction
table
has many fields that deal with data collected on birds captured in
nets,
and
is in one to one relationship with tables with specialized data on
particular
birds. This is where I see a subform for data entry being useful.

If both master tables could be used in the same data entry form, then
subforms would be feasible for the junction table. Is it possible for
two
tables to be in the same form, each with their own primary keys, and
then
to
use the junction table as a subform?

Thanks,

LAF

"Paul Overway" wrote:

I think you're misusing or misinstanding keys. You should have a PK
in
Event, another PK in Subject, and 2 FK (EventID and SubjectID) in the
junction. You shouldn't be putting an FK in either of the master
tables.
Example

Event
1 Gala
2 Dinner

Subject
1 Funding
2 Purpose

Junction
Event Subject
1 1
1 2
2 2

In the example above, I've omitted one of the possible combinations.
Nevertheless, we can see for the Gala the subject will be Funding and
Purpose, whereas for the Dinner the only subject will be purpose. If
you
have a subform for Junction on the Event form and on the Subject form,
you
can see what subjects will be discussed at the event or at what event
the
subject will be discussed.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hi Paul,

Thanks for the advice. Let us assume that there is one to many
relationship
between a master table and the junction table, for each master
table.
There
is not necessarily one to one between the two master tables.

In principle then, it appears that the best strategy is to combine
data
entry and validation for each master table separately, and then to
copy
the
primary field to the data entry form for the junction table. I
assume
that
there would be no problem with referential integrity to have a new
record
in
a master field with no foreign key, yet, put in a new record in the
junction
table. Is this correct?

Thanks,

LAF

"Paul Overway" wrote:

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a
multi-table
query and use the form for data entry. However, there are some
important
issues. Let us assume a simple database with two master tables
and
a
junction table. One master table (subjects) has a primary key
that
is
a
text
variable. The other master table is an event table with an
autonumbered
EventID as primary key. Assume for this example that tblEventID
has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has
all
fields
from all 3 tables? For this to occur, code or macro must be
written
to
run
after the SubjectID is entered in the SubjectID field from
tblSubjecst,
to
determine if a new record should be written in the subjects
table.
If
a
new
record does not need to be made, then the SubjectsID field should
be
cleared,
but the SubjectsID value placed in the SubjectsID field from
tblJunction.

Maybe? What is the relationship between Subject and Event? If 1
to
1,
ok.
But otherwise, it seems to me subject and event should be separate
forms
with data from the junction table in a subform (if it makes sense
to
show
the related data in both places). You seem to be concerned about
duplicate
data in subject. Ok, so, do some validation before update/insert
for
subject records....and if there is a duplicate, cancel the update
and
go
to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for
tblEvent
on
the
single bound entry form. Code or macro must be written to
determine
if
the
non-primary key fields are already present in tblEvents. If they
are,
then
the EventID from the matching record should be copied into
EventID
field
on
the data entry form for tblEvents. If not, then a new record
must
be
written
into tblEvent and the autonumber copied into the data transfer
form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms
for
the
two
master tables, possibly on unbound forms that pass appropriate
values
to
the
relevant data entry forms, or to an error event? The
tblJunction
data
entry
form would start out with the passed values in the foreign key
fields.
Is
there a better strategy for dealing data entry with referential
integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound
or
unbound, you're going to need to do validation to ensure that any
new
record
is not a duplicate of an existing record. I'm not sure why you'd
have
the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key
for
either
subject or event would be passed automatically.


LAF

Thanks Paul and Bruce,

This is what makes the community group so valuable.

The issue of data entry for master tables and junction tables, with
referential integrity and cascading update, has to be one of the most general
in Access. It is completely neglected in the 5 or so books I have on Access.


The following subissues are involved in every single access data base with
referential integrity.

1. Need to determine if a new record needs to be written in neither, one,
or both master tables.

2. The master table primary key values, whether for newly written record or
previous record, need to be entered into appropriate fields of the junction
table data entry form.

I am currently experimenting with a 3-form model, one form for each master
table and one for the junction table. All 3 will be on screen. The user
will first use one of the master table forms to determine if a new record
needs to be written. If so, the data entered on this form will be used to
create the new record, and the primary key value will be copied to the
foreign key field on the junction data entry form. If a new record does not
need to be written, the primary key value that was inputted will copied to
the foreign key field (through code).

This procedure will occur for each master table in sequence. The user will
simply be left with the larger junction table data entry form with the
foreign keys filled in from the previous master table forms. Subforms can
then be used for data tables that are in one to one correspondence with the
junction table.

This is a little involved, but the code that underlies this serves for data
validation as well as entry. My question thus becomes: is there a simpler
way to get the foreign key values on the junction table data entry form?

All the best,
LAF


"Paul Overway" wrote:

It makes sense because birds are being captured collectively as a group in
nets. If they were being captured individually, the junction would be
unnecessary....a bird would be related to events in a one to many. But
because the birds are captured collectively, the junction is used to resolve
what birds were captured during an event and vice versa.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"BruceM" wrote in message
...
Interesting discussion, but it leaves me wondering how tblEvents and
tblBirds
are related many-to-many unless an individual bird could be captured
several
times. I see how each event could involve many birds, but not the other
way
around. What relationship is the junction table resolving? I would have
imagined based on my understanding of the question that it would be Events

Birds Bird Details in a cascading one-to-many relationship, with nested
subforms. I don't really need an answer, but I am a bit curious as to how
this discussion will unfold.

"Paul Overway" wrote:

Ah...ok. I see what you're trying to do now.

I'd have a single unbound entry form for this, with 2 listboxs...one for
Birds, and another for Events. I'd have an Add button that would add a
record to a subform for the Junction data. I'd use the selections from
the
2 listboxes in the link master/link child property for the subform, which
would allow you to see how the 2 master tables are related and the
junction
data for that combination.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hello All,

Thanks for the stimulating discussion. Let me go back to the original
problem. The data entry form is not to look at records, it is for
entering
(and validating) data. I don't see how a subform for the junction
table
can
be used appropriately with a form for just one of the master tables.
The
foreign key for the other master table will be present, but the data
entry
needs to go into the primary key of the other master table.

By the way, the database I am developing is for capturing birds in mist
nets. We put numbered aluminum bands on the legs of birds we capture.
tblBirds lists each individual by band number (=BirdID) as the primary
key,
with other fields such as species, leftleg, rightleg (for those birds
on
which we place color bands as well). tblEvents lists each capture
event
by
site, date, and time. The EventID is an autonumbered field that is
based
on
unique combinations of site, date, and time. The junction table deals
with
the many to many relationship between BirdID and EventID. The junction
table
has many fields that deal with data collected on birds captured in
nets,
and
is in one to one relationship with tables with specialized data on
particular
birds. This is where I see a subform for data entry being useful.

If both master tables could be used in the same data entry form, then
subforms would be feasible for the junction table. Is it possible for
two
tables to be in the same form, each with their own primary keys, and
then
to
use the junction table as a subform?

Thanks,

LAF

"Paul Overway" wrote:

I think you're misusing or misinstanding keys. You should have a PK
in
Event, another PK in Subject, and 2 FK (EventID and SubjectID) in the
junction. You shouldn't be putting an FK in either of the master
tables.
Example

Event
1 Gala
2 Dinner

Subject
1 Funding
2 Purpose

Junction
Event Subject
1 1
1 2
2 2

In the example above, I've omitted one of the possible combinations.
Nevertheless, we can see for the Gala the subject will be Funding and
Purpose, whereas for the Dinner the only subject will be purpose. If
you
have a subform for Junction on the Event form and on the Subject form,
you
can see what subjects will be discussed at the event or at what event
the
subject will be discussed.

--
Paul Overway
Logico Solutions
http://www.logico-solutions.com


"LAF" wrote in message
...
Hi Paul,

Thanks for the advice. Let us assume that there is one to many
relationship
between a master table and the junction table, for each master
table.
There
is not necessarily one to one between the two master tables.

In principle then, it appears that the best strategy is to combine
data
entry and validation for each master table separately, and then to
copy
the
primary field to the data entry form for the junction table. I
assume
that
there would be no problem with referential integrity to have a new
record
in
a master field with no foreign key, yet, put in a new record in the
junction
table. Is this correct?

Thanks,

LAF

"Paul Overway" wrote:

Comments in-line

"LAF" wrote in message
...
A great strength of Access is the ability to base a form on a
multi-table
query and use the form for data entry. However, there are some
important
issues. Let us assume a simple database with two master tables
and
a
junction table. One master table (subjects) has a primary key
that
is
a
text
variable. The other master table is an event table with an
autonumbered
EventID as primary key. Assume for this example that tblEventID
has
fields
EventID, Site, Date, Time.

Issue 1. Should there be a single bound data entry form that has
all
fields
from all 3 tables? For this to occur, code or macro must be
written
to
run
after the SubjectID is entered in the SubjectID field from
tblSubjecst,
to
determine if a new record should be written in the subjects
table.
If
a
new
record does not need to be made, then the SubjectsID field should
be
cleared,
but the SubjectsID value placed in the SubjectsID field from
tblJunction.

Maybe? What is the relationship between Subject and Event? If 1
to
1,
ok.
But otherwise, it seems to me subject and event should be separate
forms
with data from the junction table in a subform (if it makes sense
to
show
the related data in both places). You seem to be concerned about
duplicate
data in subject. Ok, so, do some validation before update/insert
for
subject records....and if there is a duplicate, cancel the update
and
go
to
the preexisting record or prompt the user to do so.


Issue 2. A bigger problem occurs when data are entered for
tblEvent
on
the
single bound entry form. Code or macro must be written to
determine
if
the
non-primary key fields are already present in tblEvents. If they
are,
then
the EventID from the matching record should be copied into
EventID
field
on
the data entry form for tblEvents. If not, then a new record
must
be
written
into tblEvent and the autonumber copied into the data transfer
form.


This seems very similar to issue 1, and the solution is as well.

The big question is: should there be separate data entry forms
for
the
two
master tables, possibly on unbound forms that pass appropriate
values
to
the
relevant data entry forms, or to an error event? The
tblJunction
data
entry
form would start out with the passed values in the foreign key
fields.
Is
there a better strategy for dealing data entry with referential
integrity
and
cascade updating.

Yes 2 forms....with a subform for the junction data. Whether bound
or
unbound, you're going to need to do validation to ensure that any
new
record
is not a duplicate of an existing record. I'm not sure why you'd
have
the
junction data on yet another form, if it is related to the master
tables....just use a subform if possible....then the foreign key
for
either
subject or event would be passed automatically.


LAF