FIT 100
Lab
Activity 12: Introduction to Relational
Databases
through Microsoft Access
Creating
tables for data storage
.pdf version of this document
Reading
to be done for this lab:
·
Chapter 20 of Fluency
with Information Technology:
Foundations and Fundamentals of Information Technology
Create the Database Structure:
Identify the Important Entities and
Relationships:
Introduction:
The last part of the FIT 100
Course is a study of databases, and in particular, relational databases. We will use Microsoft Access as a way to
demonstrate concretely the various layers of complete database
architectures. Relational Database
Management Systems usually consist of Data Services:
- Data storage
- The data storage engine and
- The query processor.
Many RDBM systems do not include a Logic or Presentation layer in the application. However, Microsoft Access is an application environment that allows you to provide Data Storage, Logic Services and Presentation Services all from the same application:
Data Services
The main unit of data services (data storage) is a Table. Data storage allows for persistent data (the data stays even when the power goes off). A table is a collection of data about a specific topic.
Tables organize that data in columns
(called attributes) and rows (called records).
One of the attributes (columns) of the table is almost always a number
data type that is used as a key. A key
is used to uniquely identify the data in a particular row. Key values must be
unique and not null. A primary key is
just the attribute(s) that have been designated as the main key for the table.
Data Services also includes the storage engine and the query engine which deal with the saving, accessing and manipulation of the data. A Query is used to access, view and manipulate the data. Queries are also called views because they are a user’s “view” of the data in the database. A query that selects certain data from one or more tables and returns results is also called a virtual table.
Logic Services
This area deals with the processes that control the more complex logic determining a user’s manipulation of data in the Data Services level. Logic is usually implemented in the code module of an application. In Access, the language used in the code is VBA, Visual Basic for Applications. Your interaction with logic services for this project will be minimal. You will use simple queries to gather data from tables.
Presentation Services
The interfaces created to allow users of the Database application the ability to enter data and to view output of data. A Form is the typical interface used for input and output of data that goes through logic services and talks to the Query Engine. There are other interfaces in Access such as Reports and Data Access Pages, but you will only be dealing with Forms for the first part of the next Project. Forms are a way of entering data into and viewing data from one or more tables.
In today’s lab the main focus will be on Data Storage: creating tables to hold data instances (rows of information) of the entity represented by the table.
Objectives:
- To connect the abstract concepts of Entities, Attributes and Tuples in the Relational Database Model with the corresponding objects in Access that are concrete representations of those concepts.
- To become familiar with MS Access, one of many different Relational Database Systems that can create complete database applications.
- To create tables that are associated with each other
based on a specific type of attribute, a key attribute.
Create
the Database Structure
1. Open Microsoft Access
Programs>Microsoft Access
- The first thing you have to do is save the database. This may seem weird, since other applications allow you to add text or create objects and then save, but this is what Access requires. You are defining/creating a database structure and that space will be the only way to access the tables and queries created in it.
- Select the radio button that says “Blank Access
database” and click OK
Access 2000 -------------- Access XP
- When the window called “File New Database” shows up, name the database Lab12.mdb and save it to the Desktop or to your disk. [Note: the name in this and some other illustrations is Lab15.mdb rather than Lab12.mdb. You can use any filename ending in .mdb you like, as long as you remember what it was and adjust these instructions accordingly.]
- After you create the database, the next window lists
the database objects available on the left and the methods available for
creating them on the right.
- Creating a table in Design view will let you build the table from scratch, adding attributes (the names of the columns) and deciding what data types will be allowed for stored values.
Identify
the Important Entities and Relationships
The Student/Advisor Database
You are creating your first database today in order to hold/track information about two different entities: the Student entity and the Advisor entity. In layman’s terms - you’re going to create two tables: tblStudent and tblAdvisor
The Student table will hold data about, what else? Students! This table (Entity) should contain attributes for Student ID, Last Name, First Name, Major, year in school and the student’s advisor.
The Advisor table will hold data about the Advisor. This table should contain attributes for Advisor ID, Last Name, First Name and Department.
These tables are associated with each other in the following manner:
A student,
when they first enter school, is assigned an advisor to help them plan out the
courses they will take each quarter.
That student may change advisors- for example, if they change majors-
but they will only have one advisor at a time during their college career.
An advisor,
on the other hand, may have many students that they advise over the duration of
a quarter or a year.
We indicate the association
between the Advisor and the Student in the following manner:
An Advisor
may have many students that they advise, but a student will have one and only
one advisor at any given time.
The formal way to say this when
talking about the relational database model is:
There is a one-to-many relationship between the Advisor
table
and the Student table.
A one-to-many
relationship is the most common type of relationship used in the Relational
Database Model. In a one-to-many relationship, like the one between Advisor and
Student, a record in the Advisor table can be associated with many matching
records in the Student table, but a record in the Student table has only one
matching record in the Advisor table.
Here is how you
can indicate this relationship in graphical terms:
Student
Advises
(1 to Many)
Advisor
Creating
Entity Tables
2.
Double Click on “Create table in Design view” to start
building your Advisor table. The screen
that comes up will look like this:
Place notes to yourself
about what each attribute contains in the Description column. These notes are only available in this
screen. Indicate the data type
allowed for the value of an attribute in the Data Type column Place the names of the
table attributes in the Field Name column
- The Advisor table should have the following attributes:
Field Name Data
Type
AdvisorID AutoNumber (use
AutoNumber so that Access
will produce a
unique number to be
used as a Primary
Key)
LName Text (Text is one data type that
Access
uses to indicate a
String value)
Fname Text
Department Text
- The last thing to do after adding the attributes and
data types (and maybe some notes to yourself), is to indicate the
attribute that will be used to hold the unique key value in this table: AdvisorID
Highlight the AdvisorID row in table design view by clicking the area just to the left of the AdvisorID. Then click on the key icon on the tool bar.
Once you do that, a small key icon
should appear just to the left of AdvisorID.
- When you have finished establishing the Primary Key, save your table with the name tblAdvisor:
File>Save
- Close the table.
3.
Repeat steps 2A-2D, but this time create the Student table
with the following attributes and data types:
Field Name Data
Type
StudentID AutoNumber (use
AutoNumber so that Access
will produce a
unique number to be
used as a Primary
Key)
LName Text
Fname Text
Major Text
Year Number
AdvisorID Number (This is the column where you will
indicate the AdvisorID
number that
matches the student’s assigned
advisor name.
It is known as the foreign key
when used here
because it is a primary key sitting in a table
not defined as its own.)
- Save your table with the name tblStudent.
4. Can you explain to the person sitting next to you how these two Entities (tables) are associated with (related to) each other?
You now have 2 tables holding data related to 2 different entities. One is the Student entity. The other is the Advisor entity.
5. Go to the Tables Window and open tblAdvisor.
6. Notice that the table opens up in Datasheet View. This view allows us to see all instances of the advisor entity that have been entered so far.
- Right now, the datasheet view is empty. Add the following 2 instances, or rows, so that there is some data in the table:
Notice that a number appears once you put your cursor in the Lname column and start typing “Dickey”. This is the primary key for each row and it is generated by Access so that every row is unique and at no time will a null value be allowed in the AdvisorID column. AutoNumber is not always required when establishing a primary key in Access. It is simply a convenient way to assign one if an existing attribute does not exist that is known to be unique and not null.
7.
After you add the data, switch to the design view of the table
by clicking the design icon in the upper left corner of the database screen:
What is the view of the table? It is the view you first saw when creating
the attributes of the entity.
- Switch back to Datasheet View by clicking the appropriate icon now in the left corner of the database screen:
8.
Close the table.
You do not have to save tables when you enter data in the datasheet view. It is automatically saved for you. IF you change the way the
table “looks” (the display/format), then you need to save it in order to
preserve the look you have created.
Establishing Relationships
In order to enforce referential integrity among tables, and to be able to create forms based on information from more than one table (as you will for Project 3) you must establish relationships between your tables. They might be one-to-one or one-to-many or many-to-many. In order to ensure data integrity, allow Access to enforce the relationships as you create queries and forms.
9. After you have created the structures for your tables, go to the Relationships window by right-clicking on the database window:
You will then see a Show Table window:
- Add each table to the Relationship form by selecting
it and clicking Add. Do not add
each table more than one time. IF
the Show Table window does not appear when you open the Relationship form,
right click to find it.
- Close the Show Table window.
Use the drag and drop
method to show where the tables are associated
- Drag the keys that correspond to each other from one
table to the next. Once you have
placed them, an Edit Relationships window comes up.
- Check the Enforce Referential Integrity window and Create the relationship:
When you have created all the proper
relationships, your window should look like this:
The infinity symbol
indicates the “many” side of the relationship
- Save and close the Relationships Window.
10. Open up the Student table. Add 4 records of student information for yourself and 3 friends. Assign them each an advisor and place the ID number that corresponds with the advisor in the correct column:
In order to maintain data integrity, do not try to assign an Advisor ID that does not correspond to an actual advisor. Because you have established relationships between these two tables that enforce referential data integrity, you will not be allowed to do so.
11. You now have two entities in your database. They are populated with instances (rows of data). Take a look at each of your tables. What attribute in each of our tables could have been separated out, a new table created, and a key number put in its place to reduce data redundancy (the number of times we had to type in the same information)?
Normalization
Normalization is the process of efficiently organizing data in a database. Two main goals of the normalization process are to eliminate redundant data (for example, storing the same data in more than one table) and ensure data dependencies make sense (only storing related data in a table). This process has many levels involved in it. Let’s look at one of the most basic: revising a table structure when it has more than one entity described in it.
Let’s start to normalize one of the two tables you created today. This process is usually done before creating table structures, but we are going through it on a database that has already been created so that you get an idea of how it is done.
12. Currently your database consists of two tables. The Student table includes in it textual information about another potential entity.
This means there is the possibility that values in some of the columns may be filled with redundant information. Can you identify the column that holds semantic (textual, meaningful) information about a separate “thing” in the student table?
Breaking One Table Into Two
13.
Add a table called Major to hold the list of majors that a
student can declare.
For our database, a student will only be allowed to declare one major.
This will maintain a one – to - many relationship between the Student and Major
entities.
14.
Create a table in design view. This table will be called tblMajor. The table should have the following
attributes: MajorID as the Primary Key and MajorName as a text
attribute.
Refer to step 2 to create this table if needed.
15.
Save the table as tblMajor and close it
16.
Use the data in this table and associate it with the Student
table. To do this requires removing one
attribute and adding another attribute to the Student table.
- What attribute will we add to the Student table?
- What will we remove?
- Are there additional themes represented in the Advisor table that should be removed? (Not required, just identify them)
17. Open the tblStudent table in Design view. Do this by clicking once on the Student table object and then click the Design icon above,
We will no longer use the attribute Major as a text data type. Since you already have a couple rows of data in that column, it will be easier to delete the attribute at this point and then create another new field called MajorID, this time with a number data type.
- Select the field Major, right click the mouse. From the menu that pops up, select Delete Rows,
B. When
asked if you want to “permanently Delete the selected fields….”, click
Yes.
18.
Now the old attribute Major and all the corresponding data in
your table have been removed. Insert a
new row right above the field Year.
- Select the Year row, right click and select Insert
Rows.
A new row will be inserted between FName and Year.
- Add a new field (attribute) to the table Student
where you inserted the row.
- Name it MajorID and make the data type a number.
This is where you will store the key number that corresponds with a particular instance of the Major entity. It will be placed in the Student table as a way to indicate the major that the student has declared. (It’s the same as the way you have added the attribute AdvisorID as a number data type)
- Save and close the table.
19. There are now 3 table structures created to hold instances of the entities Student, Advisor and Major.
- Add the Major Table to your relationship window.
Associate the Major table with the Student table based on the MajorID. Create the relationship and enforce referential integrity.
20.
Close the database completely and SSH your .mdb file to your
Dante account. You will use it again in
the next lab.
NOTE: If your database is open
when you upload, you may end up loading an empty file. (Depends on the version of Access and the
OS)