The Employee section of the db seems to be expanding. I'm still struggling
to work it out. As far as I can see, there seems to be some 1:1
relationships. As it stands now, there are at least 3 junction tables. One
thing is clear though, no matter how I work this, there will be empty fields
in some of the tables. I guess I *am* going to have to live with it.

One-to-One relationships are less common than 1:m and m:m, but in your
case it may very well be applicable. They are typically used when you
are sub-typing. The following is an excerpt from a recent post by resident
guru Ken Sheridan that talks about this type of relationship (I couldn't
possibly explain it any better). Hopefully he won't mind that I reposted his
comments. The thread in question is about setting up a Church db, so
you will see references to the Church of England etc., but the concept
may be helpful in your situation.

************************************************** *

When it comes to people connected to the church in some way or other things
get a little more complex, but not frighteningly so, as the principles
involved are quite simple. All people share certain attribute types of
course; we all have names, an address, a date of birth and so on. So there
is an entity type People with these common attribute types, and a table can
represent this attribute type. People with different roles may well have
attribute types which are specific to their role, e.g. a pastor is likely to
have attribute types which a member of his congregation would not have. If I
can use an example from the C of E an attribute type for a C of E priest
might be Date of Ordination. So the entity type Pastors is a sub-type of the
entity type People. The way a sub-type is modelled in a relational data base
is by means of a one-to-one relationship. In the case of People and its
sub-type Pastors this would mean that there would be a table people with a
numeric primary key PersonID (don't use names as a primary key, they can be
duplicated), and a Pastors table also with a numeric primary key PersonID
(you can call it PastorID if you wish, but I prefer to keep the column names
the same). In the case of the Pastors table PersonID would also be a foreign
key referencing the primary key of People. The people table would have
columns for the common attributes like names and address etc., the Pastors
table would have columns only for those attribute type specific to the
Pastors entity type, e.g. Date of Ordination, but not the common attributes
like names and address.

A sub-type can of course have sub-types of its own; Chris Date in one of his
books gives the example of a type Employees with sub-type programmers, and
sub-types of programmers, System programmers and Application programmers.

As far as the primary keys are concerned, if you use an autonumber column
you can only do so for the topmost type, e.g. you could have an autonumber
PersonID column in the People table, but the primary key of Pastors or other
sub-type of people must be a straightforward long integer number data type,
not an autonumber.

When it comes to events connected with a church you need to think carefully
about how these fit into the model. One thing you need to be careful of is
deciding whether an event type is a sub-type of another type, or whether the
type of an event is an attribute type of a single entity type. You might
have a topmost Events entity type with attribute type such as Event Date,
Location etc and a Baptisms sub-type with attribute types such as ChildID,
FatherID, MotherID, all three referencing the People table. Another way of
modelling it would be to have a single Events table with an attribute type
EventType, in which a value 'Baptism' would be entered. The problem with the
latter approach of course is that if you also have ChildID, FatherID,
MotherID columns these won't be appropriate to other types of events in the
same table. In this case therefore a type/sub-type model is probably the
most appropriate. In the case of other entity types, however, the second
approach might be more suitable. To take an extreme example, in a personnel
database you would not have an Employees table and a separate table for every
Job Title in the organization; you'd be more likely to have a Positions table
and an EmployeeHistory table with EmployeeID, PositionID, DateFrom and DateTo
columns to model the many-to-many relationship between Employees and
positions.

************************************************** **

Hopefully this will help you. If you still have questions, as Bruce said it
may be helpbul to start a new thread. He and I may be the only ones
still following this thread. If you need to repost, it may be helpful if
you include some more detailed information about your Employees table
such as;

1) What different types of employees you need to track

2) Which attributes are common to *all* employees

3) Which attributes are specific to only certain employees.

--
_________

Sean Bailey


"Aria" wrote:

I'd like to address this part of your post 1st, Bruce:

It would probably be best to keep a single thread going. Beetle and I may
end up saying the same thing, or slightly different things about the same
topic, in the two branches of this thread. Since there is more information,
including discussions of master keys and other matters, in the other thread,
let's keep the discussion there.

...as you wish. I confess my ignorance here; all of this is new to me
(Access and posting). Before I was referred here by someone in my district, I
had never heard of a newsgroup/discussion group before. I had never posted
anywhere at anytime. I didn't realize I was creating additional threads. I
think I may have messed up this thread too. I'm just not sure how all of this
is supposed to work. I read the Getting Started section and read a lot of
posts before launching my own but... My apologies for any confusion I may
have caused.

Your tblLocks is heading in the right direction. Let me suggest LocationID
rather than RoomID (in case the lock is to a building or a stadium or
something), and tblLocations instead of tblRooms. You could have a field in
tblLocations to identify the Location type (Room, Closet, etc.). Wing,
Campus, etc. are attributes of the Location. If you have linked to
tblLocations, all of the information in tblLocations is available (including
Wing, etc.). No need to store such items in the Locks table.

I think your suggestion is perfect and rectifies the limitations encountered
with tblRooms. I have made the changes and am working on incorporating this
into the db.

Update-
Upon further reflection, I have scrapped tblSubs. No one cared for that
table except me.(smile) I thought it made sense, but I don't have any
experience in this area so I defer to your judgement and suggestions.
I am continuing to have problems with tblEmployees. It seemed so
straightforward in the beginning but now...additional issues keep popping up.
Before yesterday, I would have said that staff can only hold a single title.
I have thought of several situations where this is not true. If I have this
right, it would be a many-to-many relationship and requires a junction table.
Let me know if I've stepped off the cliff here.
I had to add a phone table because there are a possiblity of 3 phone #s that
a staff member may have aside from the room phone#, which I moved to
tblLocations per our previous discussion. I think this is a 1:M relationship.
We also discussed department affiliation but I can't recall an instance
where staff will belong to more than one department.
The Employee section of the db seems to be expanding. I'm still struggling
to work it out. As far as I can see, there seems to be some 1:1
relationships. As it stands now, there are at least 3 junction tables. One
thing is clear though, no matter how I work this, there will be empty fields
in some of the tables. I guess I *am* going to have to live with it.

--
Aria W.


"Beetle" wrote:

Huh? tblKeysEmployees? Not KeyID (FK to tblKeys)?

Yes tblKeysEmployees because that is the table that is used to track which
employee has which key at a given time. If you put KeyID in tblSubs to
assign keys to subs, then you have the same problem you had with
tblEmployees. A sub will use more than one key, so you have to add
additional records for the same sub.

So you have to add another field in tblKeysEmployees as a foreign key
to tblSubs. You can't use the existing EmployeeID FK because subs
wouldn't exist in that table. So now you have at least one empty field
for *every* record in tblKeysEmployees (either EmployeeID or SubID
would be an empty field). That's what I mean when I say you end up
with empty fields either way.

However, there is a way to solve both problems, which I should have
mentioned in my last post, but it involves - yes, that's right -
ANOTHER TABLE...AAAAARRRRGGGGHHH! g

You reduce tblEmployees to only those fields that apply to *all* personell
(full time and subs), then you add another table for the data that
applies to only *some* employees, and relate it back via EmployeeID.

Serenity Now!g
--
_________

Sean Bailey


"Aria" wrote:

I have read and reread your comments and suggestions. I am commenting on the
following:

Does school data need an additional table based solely on instuctors
teaching more than one subject? You are correct though. Teachers can teach
more than one subject. I only ask because you said, "additionally", which
implies that this will need a new table regardless. Other than "Subject", I
don't understand how I would be entering the same information again and
again. What am I missing?

In my opinion it should be in separate tables regardless. I don't know
how Classification and Title relate to your employees, so for now I'll
use Dept. Name and Subject as examples. As your table is currently
designed, each time you enter an employee record the user will have
to manually type in the Dept. Name and Subject. This is not only extra
work, it also invites spelling errors and invalid data in your table.

...and the light goes on. Of course! How could I have missed *that*?!

Which tables should DeptID/SubjectID go in? Good question. I think this is a
very important part of your application that you have not completely
defined yet. In a relational database like Access, it is not only imerative
that
you determine what relationships you have, but what *type* each relationship
is.

I follow you. That was a great explanation. I understand and will be
thinking about this further.

A Campus would usually encompass more than one building, a building
may have more than one wing, and a wing may have more than one room.
So, again, if we break it down to LCD (so to speak) a room is only indirectly
related to a Campus, it's direct relationship would the wing in which it is
located (or perhaps the building if that building has no "wings"). However,
as Bruce correctly pointed out, what we are really talking about is locks,
so it should probably be broken down to that level.

Again, I follow what you're saying and having had time to think about all of
the information that both you and Bruce pointed out, I agree. He is correct.
He also threw in a monkey wrench. I did not want to hear about a Locks table
when I was having trouble with the tables I already have. But he posted
something in his reply that just knocked the wind out of me, but it opened my
eyes to see what he was saying.

I hadn't thought about Master keys. You may want to consider a separate table
for those, since they have a different type of relationship with the locks
than
the regular keys.
MasterKeys
MasterID
EmpID
KeyID (FK to tblKeys)?

I don't understand. If I add the substitute staff to the our employee table,
most of the fields will be empty.
OK, I can see where that is a little tricky. Still, I think I would just
list them
in the employee table and live with a few empty address fields. If you have
them in a separate table, then you're going to have to add another FK
field to your tblKeysEmployees, so either way you end up with empty fields
in one of your tables.

Huh? tblKeysEmployees? Not KeyID (FK to tblKeys)? You know I don't know what
it is about this table that makes me want to keep it. I respect your opinion
and will probably rue the day that I didn't follow your advice; especially if
I have to post back and have someone extricate me from my own dumb mistake
(be kind if that happens!). After all, I came here for advice. I think it's
all of the empty fields that I'm going to have. They bother me. They won't
need the inactive field or the "Subject", "Address", or all of the Emergency
Contact info (Hospital, Emergency Contact, Medications, Allergies, etc.) I'm
still thinking about this one.
Again, my sincerest thanks for your help. This has been eye-opening. Both
you and Bruce have shown me how to think about some of these problems in a
different way. You both pan wide and then zoom in on the tiny details that
are easily overlooked by novices. It's easy to answer the cut and dry
questions. But someone who takes on a rock bottom beginner and walks you step
by step through the process...well, that's extra special.
--
Aria W.


"Beetle" wrote:

Does school data need an additional table based solely on instuctors
teaching more than one subject? You are correct though. Teachers can teach
more than one subject. I only ask because you said, "additionally", which
implies that this will need a new table regardless. Other than "Subject", I
don't understand how I would be entering the same information again and
again. What am I missing?

In my opinion it should be in separate tables regardless. I don't know
how Classification and Title relate to your employees, so for now I'll
use Dept. Name and Subject as examples. As your table is currently
designed, each time you enter an employee record the user will have
to manually type in the Dept. Name and Subject. This is not only extra
work, it also invites spelling errors and invalid data in your table. The
correct way is to have separate "lookup" tables that store all possible
Departments and Subjects. These would be very simple tables that would
likely just have a few fields like;

DeptID
DeptName

SubjectID
SubjectName

Then you would use DeptID and SubjectID as foreign keys in other tables.
In your data entry forms, you would typically use combo boxes to allow
users to select the correct Dept./Subject from the list of choices.

Which tables should DeptID/SubjectID go in? Good question. I think this is a
very important part of your application that you have not completely
defined yet. In a relational database like Access, it is not only imerative
that
you determine what relationships you have, but what *type* each relationship
is. Is it One-to-Many? Is it Many-to-Many? If it is 1:m, then the PK field
from the "One" side table goes in the "Many" side table as a foreign key. If
it is m:m, then you need a third (junction) table to define the relationship,
like your
tblKeysEmployees. You said a teacher can teach more than one subject,
and, presumably, a subject can be taught by more than one teacher, so
this relationship is m:m. Therefore, you not only need another table to
define the list of available subjects, but also a junction table to define
the relationship.

Again, this is wrong. Campus, Wing and RoomType are not attributes
of the Key. This table should have RoomID as a foreign key to tblRooms
and probably not much else, unless you store some other descriptive
information about the key itself, like "color" or something. Think of it
this way - you said you don't really track filing cabinet keys so we'll
just take rooms into consideration here. A key opens a room. Period.
The Room Type and the Wing in which that room is located are attributes
of the Room, not the Key. Likewise, the Campus that Wing is located in is
an attribute of the Wing (not the Room or the Key). You should have separate
tables for Campus' and Wings

Point taken; although I don't understand why the campus location is not a
room attribute. I need to know where that room or storage room is
located(especially since storage rooms don't have room #s). Does it make a
difference if there are only 2 campuses? No? So, is it CampusID (FK to
tblRooms)? Same for tblWings?
Also, I meant to put KeyType (Storage, Classroom, Gate Master, Grand Master,
etc.) as a field here.

As I stated in my reply to Bruce, I don't think I worded this part of my reply
very well. I was trying to point out that things like RoomType are not
attributes
of a key. I actually think bruce is right about this. When you break things
down
to lowest common denominator, all a key does is open a lock (or many locks if
it is a master key). Where that lock is located is an attribute of the lock,
not the key. As far as whether the Campus is an attribute of the Room? Maybe
it should be, I don't know enough about your app to say for sure. My train
of thought in my previous reply wasa basically the following;

A Campus would usually encompass more than one building, a building
may have more than one wing, and a wing may have more than one room.
So, again, if we break it down to LCD (so to speak) a room is only indirectly
related to a Campus, it's direct relationship would the wing in which it is
located (or perhaps the building if that building has no "wings"). However,
as Bruce correctly pointed out, what we are really talking about is locks,
so it should probably be broken down to that level.

Good point; I'll change this. Your second sentence is not exactly true. Just
to clarify, key assignments are based on job title and extracurricular duties
(coaching, tutoring, special projects, etc.). Masters allow all access per
location. So one key may open one or many doors.

I hadn't thought about Master keys. You may want to consider a separate table
for those, since they have a different type of relationship with the locks
than
the regular keys.

I don't understand. If I add the substitute staff to the our employee table,
most of the fields will be empty. They are not required to disclose their
address or emergency info. There address is on file with the district. In
addition, they are not bound to teach any subject in particular. If there is
a request for a P.E. instructor but they normally teach English, they are
free to accept the position for the time requested. This is why I am adding a
"Preferred Subject" field. I want the sub to enjoy there time teaching and
the permanent staff to feel comfortable with whomever is taking over their
class. I am often asked for recommendations; I'd like some info to go along
with that. If we have a long-term position for a Special Education
instructor, I need to know who has that credential so we can move ASAP. Oddly
enough, the district doesn't track this info; I've asked. If I have the subs
in their own table, I think all the info I need will be together.

OK, I can see where that is a little tricky. Still, I think I would just
list them
in the employee table and live with a few empty address fields. If you have
them in a separate table, then you're going to have to add another FK
field to your tblKeysEmployees, so either way you end up with empty fields
in one of your tables.

Thank you for saying that! I kept wondering,"Why am I having such a hard
time with this?" Why am I still on the pen, paper and diagram stage?
I like a challenge because it makes success that much sweeter but *come
on*...! It makes it difficult to make a move when you are about ready to step
off the cliff at every turn. If it weren't for this discussion group, I would
have. Thanks to both you and Bruce for posting your reasons and thought
process along with your comments. I don't know about others, but it helps me
to follow along. I t takes an extra measure of patience that I appreciate. I
am going to rethink my tables and post them again. I hope you will take a
look and tell me what you think.

Yeah, you kind of jumped right into the deep end of the pool, but hopefully
with help from the group here you'll get it all sorted out. You'll get
differing
opinions from people too, so sometimes you just have to absorb the different
ideas and then decide what you think will work best for you.

--