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\me{Harris, Dey}	% author(s) names and/or email address
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\docheader{Introduction to Computing}
{9}   % module number
{Database Management Systems}  % module name

\begin{goallist}

\item Students will recognize components of a database: records, files, and tables
\item Students will identify types of problems relevant to database management applications
\item Students will create a flat - file database
\item Students will understand input tools, processing tools, output
\item Students will identify key features of forms, queries, reports, indices.
\end{goallist}


\begin{prereqs}

\item Essence of computation
\item Spreadsheet concepts

\end{prereqs}

\section{Databases and Database Management Software}

One of the most powerful applications of computers is the capability
to store, organize, and retrieve large quantities of data.  An
organized collection of data is referred to as a database.  The
programs designed to manipulate databases are known as database
management systems, commonly abbreviated as DBMS.

The purpose of databases is to make large amounts of information
easier for humans to understand.  Databases do not necessarily require
the use of a computer.  You probably already maintain several
databases without even knowing it!  Any time you keep track of
information with some type of organized system, you are managing a
database.  Your calendar, personal phone book, and 'to do' list are
all databases, even if you commonly write them with pencil (or
crayon!)  The telephone book is a database.  Any time you keep a list
of any sort, you are forming a sort of database.  Databases have been
an important information management tool since written language began.

Keeping track of information by hand has some shortcomings.  Written
lists can get very unwieldy if you have more than a pageful of
entries.  This problem is compounded if the information is not
organized in some fashion like alphabetic order.  This process of
sorting is very tedious when done by humans.  Anyone who files papers
in an office knows how easy it is to misplace files when humans are
responsible for keeping them in alphabetical order.  Every time a new
document is created, it must carefully be placed in the right spot.
If it is ever 'taken out' and not replaced properly, it may never be
found again.

The searching process can also be difficult.  Looking up a word in a
dictionary or a number in a phone book can be a frustrating experience
if the word or name you are looking for is not spelled as you
expected.  Finally, these manual systems of organization can be quite
clumsy when we want to find information in more than one way.  For
example, if you have a person's name, and you want their phone number,
you can go to the phone book to find it.  But what if you have the
phone number or address, and not the name?  A traditional phone book
is almost completely useless for this kind of problem.  In old
detective shows, there were books printed by the phone companies for
this type of purpose, but most people did not have access to them.  If
you think about it, the ``find a person from a number'' book would
contain {\em exactly} the same information as a traditional phone
book, just organized in a different order.  It was necessary to
recreate the entire database just to allow this amount of flexibility.
If we wanted to be able to search for the name of a person with a
certain address, we would need yet another entire book of the same
size.  With paper databases, it is impossible to search by more
complex criterion, such as ``tell me all the people that live on Poplar
Street.''

\section {The problems databases help you solve}

Electronic databases are much more flexible and powerful than their
paper ancestors.  They have made entirely new kinds of data storage
and analysis practical.  A database is called for whenever you are
interested in keeping track of information.  Electronic databases are
especially helpful when you want to store large amounts of
information, information with a lot of complex characteristics, or
when you want the capability for complex types of information
retrieval.

You will often come across a database program as a user.  Many of you
encountered such a program when signing up for this class.  The
scheduling programs of many universities have the entire course
schedule and all student schedules stored in a massive system of
databases.  You may have examined the class schedule by interacting
with such a system.  In fact, you may have been able to sign up for a
class online.  When you did so, your personal scheduling information
was added to the university database.  As a user, you can usually look
at a database, and you can sometimes even add to the pool of
information it contains.

You might also interact with a database as a developer.  In this role,
you are not as concerned with the actual information that the database
contains as you are with the general structure of that information;
how it is organized, how it can be searched, and how the users will
see it.  Although you will do this less frequently than you might
encounter databases as a user, it is a good idea to understand a
little bit about database development, because the principles will
make you a much stronger user.

\section{How databases are organized}

As you have seen, computers can only understand very rudimentary
elements.  In order to store complicated stuff like fruit, addresses,
and whatever else, we have to have some kind of organizational scheme.
Computer scientists have come up with some terms that are used to
define databases.

\subsection{Records}

The most critical unit in a database is the record.  If you think
about it, most databases are arranged around a certain kind of entity.
A phone book is a collection of telephone companies.  A card catalog
is an index to a collection of books in a library.  You might also
have a database referring to diseases and viruses, giraffes in a zoo,
video tapes in your library, or anything else.  The important idea
here is that you can think of a database as a collection of like
things.  These things don't even have to be real.  You could just as
easily have a database of dreams, monsters, or concepts.  What really
matters is that all the things in the database have to be similar.
For example, you might have a database of fruit in a supermarket.  You
might have entries in this database describing bananas, pears,
oranges, and apples, but an entry describing a station wagon might not
fit here.  It also may not make sense to have an entry for pork chops
in this database, even though pork chops might be in the same
supermarket.

Each entity in the database is one record.  If your database describes
a bunch of giraffes, one record in the database describes one giraffe.
If your database describes fruit, one record might describe one type
of fruit.

\subsection{Fields}

Each entity in a collection shares a certain number of
characteristics.  Each type of fruit might have the following relevant
characteristics:

\begin{itemize}
\item What is the name of the fruit?
\item How long can we keep it on the shelf?
\item When did it come to the market?
\item How much does it cost per pound?
\item Is this fruit spoiled?
\end{itemize}

This list of characteristics is called fields.  The fields are the
characteristics which describe one record.  All of the records in the
database must have the same fields, but the values of those fields
will be different.  For example, all of the fruit in the database will
have a name, but the names will be different.  One record will have a
name field with the value `Bananas', and another record's name field
will have the value `Apples.'  A field can be thought of as a detail
of a record.

Fields represent units of the computer's memory.  Because the computer
stores different kinds of information in different ways, each field
must have a specified data type.  When you create a database, you need
to tell the computer what kind of data each field will be so it knows
how to store the information.

Data types in databases get a little more specific than you have seen
before, because databases have more specialized ways of storing things
in memory.  Here's a few of the common ones:

\begin{description}
\item [\bf text]

You are already familiar with text from spreadsheets, but now we also
have to specify a length.  This has to do with the way that databases
find records.  All records in a database must be the same length
(number of bytes in memory), so you have to specify the length of each
text field.  You might give a field that will hold state names a
length of two characters, for example, and a 'first name' field a
length of fifteen characters.

\begin{quest}

So why not just give each text field a big length, like 500
characters?

\end{quest}

\item [\bf integer]

An integer is a whole number (no fractions or decimals) including
zeroes and negative numbers.  (...and you told that seventh grade math
teacher you would never need this stuff again!!! )  Integers are
pretty easy for the computer to work with and store.  Sometimes you
will come across long integers, which are also integers, but stored in
a different way that takes more memory but allows for larger (and
smaller) values.

\item [\bf real numbers]

Real numbers are integers and decimal values.  As you may remember,
the computer has to use a special form of exponential notation to
store them in the computer.  You might encounter 'super real numbers'
(often called double-precision real numbers) These are real numbers
that take more memory to store, but allow more decimal places.

\item [\bf logical]

Logical values (also sometimes called boolean or binary values) are
values that can be expressed in terms of 1/0, yes/no, true/false,
on/off, and so on.  Binary fields take very little memory.  (Think
about it, you know how much they take!)  They can be surprisingly
useful.  For example, in our fruit example the field that relates to
whether the fruit has spoiled might be a binary field.  Most of the
time you can direct the database to use a yes / no or true / false
notation rather than 1 / 0, but of course the 1/0 value is closest to
what the computer stores.

\item [\bf date]

As we discovered with spreadsheets, dates are not exactly text, and
not exactly numbers.  Spreadsheets usually think of them as numbers,
but databases often are a little more sophisticated about dates, and
give them their own data type.  You often have a great deal of
flexibility about how the dates are displayed to the user, but they
are stored basically as numbers.

\item [\bf other types]

There are a number of other data types available.  Many database
management systems allow you to store other kinds of stuff such as
variable-length memos, pictures, sound files, and whatever.  Some even
let you create your own data types.

\end{description}



\subsection{Tables}

So far, we have thought of a database being a collection of records.
To be more precise, a collection of similar records is a table.  All
the records in a table must have the same fields, but they can have
different values in the fields.  A table could make up an entire
database, but as we will see later, there are databases with multiple
tables.

\subsection{Index}

We expect tables to be sorted.  Think back to the telephone book
example.  The traditional phone book is sorted by last names.  The
'backwards phone book' might be sorted by phone numbers.  ``Last name''
and ``phone number'' describe fields in a database.  The field that you
use for sorting the database is often referred to as the {\em key
field}

\begin{quest}

Most of us still remember libraries with the old card catalogs. Why did they have an entirely separate cabinet for subject, title, and author?

\end {quest}

There are problems with this approach.  In order for database programs
to be effective, there must be some unique way of dealing with each
record.  It would clearly not be efficient to use 'first name' as a
primary key in a database of people in a city, because there would be
far too many people with the same name.  To deal with this, most DBMS
systems allow you to create an {\em index}.  The index solves this
problem of uniqueness with one of two strategies: Each record must
have either a truly unique field or a unique combination of fields.
The unique field strategy requires each record to have a field whose
value cannot possibly be duplicated in the database.  These fields are
usually either some arbitrary number (like your account number at the
bank or insurance company) or the old stand-by in America, the Social
Security Number.

\begin{quest}

Why is your social security number used so frequently in databases?

\end{quest}

The other strategy uses multiple fields to generate an index.  The
phone book uses the last name as a primary key, but that may not be
unique enough if you have a common last name.  If the database system
encounters a large number of people with the same last name, it then
sorts that group by the first name, then any with both the same last
name and first name will be sorted by middle initial.  Using this
combination of fields decreases the likelihood that there will be two
records with the same index.

To recap, an index is some way of using one or more fields to uniquely
identify each record in a table.

\begin{quest}

So what is the index in a yellow pages phone book?

\end {quest}

\section{The main kinds of tools in a DBMS}

A database management system is a software package that gives you a
number of tools.  These tools are related to the main problems one
might solve with a DBMS

\subsection{Data definition tools}

\imagefigg{dbdef}{Data Definition Table}{6.5}

A full-fledged DBMS will have some kind of tools for setting up a
brand new database.  Such a tool will allow you to define a record,
the fields in that record, and the data types of each field in the
record.  This is a very powerful capability.  Most of the time, you
will not need it.  It is only used when you need to create an entirely
new database.  When you are using this tool, you are acting as the
developer.

\subsection{Data manipulation tools}

\imagefigg{dbtable}{Data Manipulation}{6.5}

The data manipulation tools are the part of the database the user
interacts with most of the time.  Data manipulation consists of a
number of activities: The user will have some way of viewing all of
the records in the database.  She will probably also have a way to add
or delete records, and edit the fields of existing records.  There
will usually also be ways of sorting the records by any field in
ascending or descending order.

Often there will be large spreadsheet-looking devices on the screen
that allow you to manipulate records.  These are quite hand if you
want to compare a lot of records at a time, but they can be quite
intimidating.  Most DBMS systems have a way of using and creating
forms for user input.

\imagefig{dbform}{Form}

A form simply displays one record at a time in a less cluttered form
on the screen.  If you have to do a lot of data entry, you will
appreciate well designed forms.

Data manipulation is related to {\em input} When you use this kind of
tool, you are somehow inputting information to the system.


\subsection{Querying tools}
\imagefig{dbquery}{Query}

Often the entire database is too much information.  One main job of
databases might be to find out specific information, such as ``How many
customers do we have in California?'' or ``Which stamps in my collection
are worth more than \$500?''  You could certainly look at all the data
and count out these answers by hand, but the computer ought to
automate that kind of tedious work, and it can.  A query essentially
is a question.  It returns an answer as a subset of the table.  Only
the members of the table that answer the question are returned.
Queries are comparisons.  They always involve field names and sample
values. You tell the computer a field and ask it to search for records
that relate to a specific value.  In our fruit example, if we wanted
to find our record for ``apple'', our query might be something like

NAME = ``apple''

What this means to the database is ``Show me all the records where the
NAME field is equal to the value `apple' ''.

In fact, we might have a number of kinds of apples in our store, like
Jonathan apples, Granny Smith apples, and Macintosh apples.  (The
fruit, not the computer!)  We might be able to make a search for
fields that contain a value.  If we modify the above query to

NAME contains ``apple''

we might find all those other apples as well, (although we might also
find pineapple!)  The exact syntax of the statements will certainly be
different, but the idea will not change.  A query consists of
comparing a certain field with a certain value.

Other kinds of relationships are also possible.  If we wanted to
search for all the expensive fruit in our store, we might want to have
a query something like:

COST\_POUND > \$1.00

This query should return to us a list of all the records whose
COST\_POUND field has a value larger than one dollar.

\imagefig{dbsql}{SQL Query}

Querying is an example of {\em processing} When you do this kind of
work to a database, you are somehow massaging the values in the
database to impart some kind of meaning from them.

\subsection{Report tools}

\imagefigg{dbrepgen}{Report Generation}{6.5}

Data manipulation tools and querying tools are very handy for people
with some degree of computer skill, but often computer operators are
required to produce some sort of report with the data they have been
working on.  Report tools are a class of tools that focus on the
production of attractive output from a database.  A report is a
specially formatted subset of a table (or tables) designed explicitly
for printing or displaying on the screen.  Often a report has a list
of fields across the top, and each row of the report represents a
record.

Many times what you see in a report is not actually the raw data from the
table, but some subset of that data that is pertinent to answering a
specific question. Sometimes reports are listings only of the results
from a specific query, although they could also be the entire table if
we wanted. Most reports do not list every field in the table.  For
example, if we wanted to make a report of the prices of our fruit, we
might only include the NAME and PRICE/POUND field.  The other fields
are still there, but we don't have to include them on our report,
because they would distract from the report's main job, listing the
prices.  (We might have another report to list values of other fields)
Sometimes reports contain values that have been calculated from other
fields.  For example, if we had a POUNDS field for our fruit that
showed the number of pounds of each type of fruit on hand, we might
want to have a column of our report that contains the calculation
COST\_POUND * POUNDS.  (Wow, that looks a lot like a spreadsheet
formula, doesn't it?)

\imagefigg{dbrep}{Report}{6.5}

Reports do not have to look like tables.  Other common report formats
are mailing labels and mail merge letters.  (Have you ever gotten mail
from Ed McMahon?  Are you impressed that he took the time to type a
letter with your name and address in it?)  The formatting is different
in these types of reports, but the process is the same.  Pieces of
data from the database have been pulled out and integrated into some
sort of document for printing and display.

\section{Creating a database}

Creating databases is an art form.  People make their living doing
it. You have the skills to build a simple database, and you should
know enough now that you can start exploring the more advanced topics
on your own.

To build your own database, you follow the same general steps
regardless of your specific DBMS software.

\begin{enumerate}

\item STAIR!  (You KNEW you couldn't get through a chapter without
seeing that acronym!) State the problem and identify the tools you
might use. Specifically, answer these questions for your particular
database:

\begin{itemize}
\item Why do I want this database?  
\item What kinds of information do I want to keep track of?
\item What are the entities (will become records) I am keeping track of?
\item What are the characteristics (will become fields) of each of
these entities?
\item What kind of input features do I want?  (forms, a spreadsheet - thing?)
\item What will my index be?
\item What kinds of questions do I want to ask with this data? (queries)
\item Do I need any special reports?
\item What software will I use to develop this database?
\item What tools does it have to solve each of the problems above?
\end{itemize}

\item Create the table.  To do this, you will need to create a
template for the records.

\begin{itemize}

\item Create a template for the records

This means defining all the fields that constitute a record.  Think
hard about this, because you don't want to change the record
definition once you have started adding data to the database.

\item Create the fields
For each field, identify the field name and type (and length if necessary)

\item Continue until all the fields of the prototype record are done.

\end {itemize}

\item Add information to the database.
While you are still testing, you shouldn't add too much information,
because it may get messed up.  You should put in enough so that you
can tell it will work.  You should also anticipate errors the user
might make, like typing in ``four'' instead of putting a 4 in a numeric
field.  Try making some of these mistakes on purpose, and see how the
database responds.

\item generate any forms to aid user input.  

There will usually be some sort of tools available to help you in this
process.  If the database is simple, this step may not be necessary.

\item create any reports you need for output

Again, this may not be necessary, or there may be a number of reports
you want to generate from the database.  You will probably find some
kind of tool to help you with this process as well.  This process may
require building queries to limit the number of records shown in the
report.

\end {enumerate}

\section{Types of Database systems}

As you have seen, databases can be very complex, and their
maintainance can be more involved than some of the other applications
we have examined.  There is a very wide range of application software
for database management.

\begin{description}
\item [\bf Read - Only Databases]

These are databases that have already been established, usually by a
professional programmer or team.  You interact with these databases
only as a user.  You can make queries of such a database, and
sometimes make reports from them.  Some examples: the Internet search
engines, on-line card catalogs, airline reservation systems.

\item [\bf Pre-defined databases]

These databases are often commercially available, and are a shortcut
for people who want to manage a database, but don't want to build it
themselves.  Often these are aimed at a specific topic in the business
or home market such as wedding preparation, video library management,
invoice handling, inventory, or payroll.  In such a database, all the
design has been done for you, and usually a number of queries and
reports are also pre-defined, although you may have the capability to
create more of your own.  The advantage of this type of database is
that you don't have to do the hard work of defining data types, so you
can concentrate on adding and manipulating data.  The down side is
that you are stuck with whatever design the programmer gave you.  If
you want something more specific to your needs, you are out of luck.

\item [\bf Flat - file DBMS]

These systems generally allow you to do the things we have been
talking about, although inexpensive systems may have limited capacity
in particular areas.  A flat file DBMS is capable of handling only one
table at a time.  For home use, this is often just fine.  You don't
need any more to deal with your Christmas card list, or stamp
collection inventory.  The user-friendliness of DBMS software varies
tremendously.  Some systems (particularly the database packages
bundled with integrated suites) are relatively easy to use and provide
point - and - click interfaces.  Other DBMSs are nothing more than
programming languages - a list of commands that you have to put
together on your own.  In general, DBMS applications are more involved
than other standard applications.

\item [\bf Relational DBMS]

These are the mainstay of the database world.  A relational database
is much like a flat file database, except it allows the use of
multiple tables.  Imagine the following example:

A programmer has been hired by a garage to create a database for their
operations.  After talking closely with the owners of the garage, she
notes three main needs:

\begin{enumerate}

\item They want a way to keep track of each part in the inventory.
When a part is used for repair, it should be noted, so the owners can
order new ones.

\item They want to keep track of the customers who use the garage.
When Mrs. Jones, comes in, for example, they would like to know what
services she has ordered in the past, and what has already been done
to her car.  They also want to send her postcards informing her of
special deals and tune-up times for her car. This will increase
efficiency and customer service.

\item They want to keep track of each transaction.  This database will
be closely tied to the cash register and should give a report that
explains exactly what has been done to her car, and should be a very
nice receipt.

\end{enumerate}

At first, it may seem like three entirely different databases are
necessary. Although the customer database may share some information
(like part numbers) with the inventory database, it appears to be a
different database.  It will certainly require a different table,
because the fields that describe a part in the inventory are very
different than the fields that would describe a customer. Likewise,
the receipt table may share some fields with other tables in the
system (customer name and part number) but the fields that describe a
receipt are clearly different than those that describe a part or those
that describe a customer, so a third table is necessary.

What we see here is three distinct tables that share some fields with
each other.  These tables are distinct but {\em related}, thus the
database is a {\em relational} database.  (Just when you think you can
count on those computer scientists to come up with a completely
meaningless term, they give you one that makes sense!)

The big DBMSs like Oracle, Paradox, Access, and so on are examples of
relational databases.  Like flat - file database management systems,
these DBMS packages come in all flavors, from fairly straightforward
point - and click to cryptic but very powerful programming languages.
\end{description}

\section{Databases and Ethical Concerns}

Any tool with as much power as databases can give must have some
caveats, and databases certainly do.  Databases are easy to build and
maintain, and there is no way to keep unscrupulous people from using
them as well as those that intend only good.  Even when they are not
deliberately used for foul purposes, databases can have unsuspected
side effects.

Privacy is a major concern of the present and very near future.
Although there have been databases since written language began, they
were often very inefficient.  There was usually little danger of the
information in a database getting into the wrong hands, because
computers tended to not be connected, and there was relatively little
information being kept.  Now the increased ease of database
development along with increases in computer connectivity, processing
and storage capacity have made the amount of information stored on
databases increase exponentially.  Now nearly every organization or
corporation has some sort of database.  When you give your name and
address to a company by entering a contest or filling out a
questionnaire, your information is almost certainly going to be
entered on a database.  That corporation is not always required to
keep the information about you to themselves.  Have you ever wondered
why you get the combination of junk mail you do?  Every one of those
things in the mailbox has a mailing label on it generated by a
database.  You may have given them the address directly, or it may
have been sold to the company by another company who you gave your
information to.

Security of information is another concern.  As more and more
computers are linked via the Internet, there are more opportunities
for data to be taken by those who should not have it.  Be very careful
using your credit card number on the Internet.  Where will it go on
the way to its destination?  Will it be carefully guarded in the
destination database, or can somebody just break in and assume your
identity?  Take the same care with other personal information.  Who
will get this information?  Do you want them to have it?  The legal
system is wrestling with issues of privacy over the Internet.
Technology is changing more quickly than the legal system can keep up.

\section{Laboratory Assignment}

\begin{enumerate}

\item Create a simple flat file database for mail merge in your word
processor.  Most word processors have a tool that allows you to create
a simple database and mail merge without having to go to a separate
document.  Your table should have at least 3 fields and five records.
Make a letter that can read the fields.

\item Use a full-fledged DBMS to create a telephone directory. Your
database should have the following characteristics:

\begin{itemize}
\item One table
\item At least three fields per record
\item At least five records
\item An index field
\end{itemize}

\item Add more advanced features to your telephone directory:

\begin{itemize}
\item A form for input
\item A report for output
\item A query for looking at specific records
\end{itemize}

Don't forget to utilize any shortcuts or tools the DBMS gives you as
shortcuts!

\end{enumerate}

\section{Summary}

The collection of information into organized bundles has been with us
for a long time, but computing technology has made the management and
manipulation of databases far more practical than it has ever been in
the past.

The software used to create and maintain databases is called database
management systems, and these systems come in a number of levels of
complexity ranging from read - only databases and pre-defined
databases to complex programming languages.

Databases are organized into tables, which are collections of records.
One record describes one discrete entity.  The properties which
describe a record are known as fields.  A field is defined using a
specific data type.  Records are sorted by indexes, which are related
to one or more key fields.

The main types of tools one might find in a DBMS relate to the
principle jobs of such a system. Data definition is the creation of
new tables, records, fields, and indices.  Data manipulation is the
act of entering information into an existing database.  Querying is
using special tools or languages to ask for sub sets of the data in
the database, and reports are output for the printer or screen which
format the information nicely.

\section{Vocabulary}
\begin{vocab}

\item [\bf Database: ]an organized collection of information

\item [\bf DBMS: ]Database Management System.  A software application
designed to help users create, maintain, and manipulate databases.

\item [\bf User: ]The person who uses a database.  The user generally
does not worry about the design of the database, ot its components.

\item [\bf Developer: ]The person who designs a database and its
complement of forms, reports, and other support materials.

\item [\bf Record: ]The central entity in a database.  One record
describes one discrete element.

\item [\bf Field: ]A detail of a record.  A field is usually assigned
a data type, and sometimes a length.  A number of fields make up a
record.

\item [\bf Table: ]A collection of like records.  All the records in
the table will have the same field definitions, but different field
values.

\item [\bf Data types: ]The type of organization used to translate
binary values into a more useful type such as real numbers, dates, and
text.

\item [\bf Integers: ]The whole numbers including zero and negative
numbers. (No fractions or decimal values)

\item [\bf Real Numbers: ]Integers and decimal vaules.  Often DBMSs
will have single and double precision real numbers available.

\item [\bf Logical Fields: ]A datatype defined by a yes / no,
true/false value.  Also referred to as binary or boolean fields.

\item [\bf Index: ]A sorting and searching tool organized by one or
more key fields.

\item [\bf Key Field: ]A field used as part of an index.  The first
one used is often called the {\em primary key}

\item [\bf Data Definition: ]The process of creating a new database,
especially the record definitions. Only the developer does this.

\item [\bf Data Manipulation: ]The process of adding new information
to the database.  This may be done by the developer and / or the user.

\item [\bf Querying: ]Requesting a subset of the database in terms of
the values of fields. Queries involve comparing some field or fields
to some value or values.

\item [\bf Reporting: ]The process of creating specially designed
output of the database.  Often tied to a specific query.

\item [\bf Flat - File: ]A type of database characterized by one table
only.  These are sufficient for much home use, but are not powerful
enough for many business applications.

\item [\bf Relational: ]A type of database characterized by multiple
tables.  The tables are different, but related.  They may have common
fields, or other types of relationships.


\end{vocab}

\anslist{abdbans}
\end{document}

dbdef.gif dbtable.gif dbform.gif dbquery.gif dbsql.gif dbrepgen.gif dbrep.gif
