FIT 100

Lab 15:  Introduction to Relational Databases
through Microsoft Access

Creating tables for data storage

Spring 2002

Reading to be done for this lab:

·         Chapter 20 of Fluency with Information Technology:  Foundations and Fundamentals of Information Technology

Create the Database Structure. 2

Identify the Important Entities and Relationships: 4

Creating Entity Tables: 5

Establishing Relationships 12

Normalization. 1

Breaking One Table Into Two: 16

 

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:
 

 

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.  You will use simple queries to gather data from tables.

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. 

 

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 Project 3.  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:

  1. 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.
  2. To become familiar with MS Access, one of many different Relational Database Systems that can create complete database applications.
  3. To create tables that are associated with each other based on a specific type of attribute, a key attribute.
     

 

1.    Create the Database Structure

A.     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.
 
 

 

 

 

 

 




B.      Select the radio button that says “Blank Access database” and click OK

 

 

 

C.     When the window called “File New Database” shows up, name the database as YourName.mdb and save it to the Desktop or to your disk.

 

 

 

 

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.

 

 

 

 

2.   

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, 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:

                        Advises

                   (1 to Many)
 
Identify the Important Entities and Relationships

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.    Creating Entity Tables

  1. Double Click on “Create table in Design view” to start building your tables.  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
 

 

  1. Create the Advisor table with 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            

 

 

  1. Identify the primary key for the table.

    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.

  1. When you have finished establishing the Primary Key, save your table with the name tblAdvisor:

File>Save

 

  1. Close the table.

  2. Create the Student table with the following attributes and data types.  (Repeat steps 2A-2D)

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

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.)

  1. Save your table with the name tblStudent.

 

  1. 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.

 

4.    Add Data to Entity Tables

  1. Go to the Tables Window and open tblAdvisor.

 

Text Box: 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. The table is currently empty.
 

 

 

 

 


  1. Add the following 2 instances, or rows, so that there is some data in the table:

 

 

Text Box: 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.
 

 

 

 

 

 

 

 


  1. After you add the data, switch to 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

 

 

 

 

 

 

  1. Close the table. 

Text Box: 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.

 

 

 

 

 

5.    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.  In order to ensure data integrity, allow Access to enforce the relationships as you create queries and forms.

 

  1.  Go to the Relationships window:

 



·         Right click while on the database window OR 

·         Go to Tools>
Relationships OR 

·         Find the icon on the Tool Bar

 

The Show Table window box should come up:

 

 

  1. 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.

  2. Close the Show Table window.

 

Use the drag and drop method to show where the tables are associated
 
    

 

  1. 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. 

  2. 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
 

 

  1. Save and close the Relationships Window. 

 

  1. 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:

 

 

Text Box: 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.
 

 

 

 

 

 


  1. 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. 

 

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? 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


6.    Breaking One Table Into Two

  1. 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.
 


 



 

 

  1. Create a table called tblMajor with the following attributes:
    MajorID as the Primary Key (use autonumber) and
    MajorName as a text attribute. 

    Refer to step 3 to create this table if needed.

 

  1. Save the table as tblMajor and close it.

To use the data in tblMajor how will we associate it with the tblStudent?  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)
 
 

 

 

 

 

 

 

 

 

 

 

 


  1. Open the tblStudent table in Design view.  Do this by clicking once on the Student table object and then click the Design icon above,

 

Domain Integrity:

There is a rule in database design that any attributes that are part of a relationship between 2 tables must have the same data type.  This is called “maintaining domain integrity”. 

 

By creating a new table for Majors with a primary key that is a number data type, we can no longer use the attribute Major because it is a text data type. 

 

The data type of any attribute holding foreign key information from the Major table will have to match.  Since you already have a couple rows of data in that column, it will be easier to delete the attribute and then create another field called MajorID, this time with a number data type.
 


 

  1. Select the field Major, right click the mouse. From the menu that pops up, select Delete Rows,

 

F.      When asked if you want to “permanently Delete the selected fields….”, click Yes.

  1. 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.

  2. Select the Year row, right click and select Insert Rows.
    A new row will be inserted between FName and Year.




  1. Add a new field (attribute) to the table Student where you inserted the row. 

  2. Name it MajorID and make the data type a number.

This attribute will hold the key numbers that corresponds with particular instances of the Major entity.  It is placed in the Student table as a way to indicate the major that the student has declared. (The attribute AdvisorID is used in the same manner.)
 
 

 

 

 

 

 

  1. Save and close the table.  There are now 3 table structures created to hold instances of the entities Student, Advisor and Major. 

 

  1. 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.

 

  1. Text Box: ALERT!! 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)Close the database completely and transfer your database to Dante.  You will use it again in the next lab.