1. Databases
Chapter 9
Asfia Rahman

2. Key terms Database: a structured method of storing data
Table: a set of similar data (about people, places, objects or
Record: a common word for entity
Entity: a set of data about one thing (person, place, object or event)
Attribute: a category of information within an entity
Field: a common word for attribute
Primary key: a field that contains the unique identifier for a record Database management system: software used to manage a database
Relationship: the way in which two entities in two different tables are connected
Foreign key: a field in a table that refers to the primary key in another table
Normal form: the extent to which a database has been normalised Index: a list of keys or keywords which identify a unique record and can be used to search and sort records more quickly
Entity relationship diagram: a diagram that represents the relationships between entities
Flat file: a database stored in a single table
Compound key: two or more fields that form the primary key Referential integrity: data in the foreign key of the table on the many side of a relationship must exist in the primary key of the table on the one side of a relationship
Query: a question used to retrieve data from a database
Parameter: data used within the criteria for a query
Asfia Rahman

3. Structure method for storing information/data in an organized way.
Database
Structure method for storing information/data in an organized way.
Tables
A set of similar data/ information about a single entity ( people, places, objects, events)
Records
A set of information about a single item. Single occurrence of an entity. One instance of an entity.
Fields
A category/single item of information within an entity
Field Value/Data
Value of the field
Asfia Rahman

4. Keys Primary Key Foreign Key Compound Key
Unique identifier for each record.
Must contain unique values.
A field in a table that refers to a Primary key in another table.
Used to create the relationships
Two or more fields combined to make a unique identity
Asfia Rahman

5. RDBMS
DBMS
Database management system – Software used to manage a database.
RSBMS
Relational Database management system – Software used to manage a database that includes relationships.
Asfia Rahman

6. Field types and sizes Text Alphanumeric Numeric (integer/decimal)
Date/time
Boolean
Different database management systems use different names for data types. If you are using Microsoft Access you will notice that text is used for alphanumeric data and number is used for numeric data. Sometimes the software will also use formatted data as a data type such as currency. Currency is actually numeric (usually decimal) and is just formatted by displaying a currency symbol with the number.
Asfia Rahman

7. Field sizes
Fields within a table will have field sizes applied to them. This is because most fields are a fixed length. This means that only a specified amount of data can be stored in each field.
Text and alphanumeric fields will have a length to specify the maximum number of characters that can be stored. For example, the Product Name in the Product table is limited to 40 characters. This avoids having lots of wasted storage space where field space is not used up if the length is too long.
Numbers can also have a field size. This could be defined as the number of digits or it could be defined as the maximum numeric value.
Dates will always be the same field size as they will always store the date in the same way, but they can be formatted to be displayed differently.
Some text fields can be formatted to be a variable length which means they can store as little or as much data as possible. These are sometimes referred to as memo or long text data types. These are useful for fields that will contain notes or comments.
Asfia Rahman

8. Field sizes in access
TIP: Use the Long Integer data type when you create a foreign key to relate a field to another table's AutoNumber primary key field.
Byte — For integers that range from 0 to 255. Storage requirement is a single byte.
Integer — For integers that range from -32,768 to +32,767. Storage requirement is two bytes.
Long Integer — For integers that range from -2,147,483,648 to +2,147,483,647. Storage requirement is four bytes.
Single — For numeric floating point values that range from -3.4 x 1038 to +3.4 x and up to seven significant digits. Storage requirement is four bytes.
Double — For numeric floating point values that range from x to x and up to 15 significant digits. Storage requirement is eight bytes.
Decimal — For numeric values that range from x 1027 to x Storage requirement is 12 bytes.
Asfia Rahman

9. ERD Entity relationship diagram
Shows the relationships between each entity.
Entity is represented by a rectangle.
Relationships are represented by a line
One to One
Sales rep
Employee
One to Many
Category
Product
Many to Many
Order
Product
Asfia Rahman

10. Erd tasks Draw ERDs to represent the following relationships:
One Airline Seat to one Customer.
One House to many Occupants.
Many Coaches to many Drivers.
Draw an ERD to represent a library model. Within the library, there are several books. There may be many copies of the same book which are known as book copies. customers can loan a book copy. a customer can have many loans but a loan will be for just one customer. Each loan will be for one book copy. but over a period of time each book copy can be loaned out many times.
Asfia Rahman

11. Erd tasks Husband Wife Describe each of the relationships Club member
Exclusive member
Book
Author
Booking
Room
Car
Service
Asfia Rahman

12. relationships
Relationships within a database can be used to connect entities together.
A foreign key is an attribute (field) in one entity that connects to a primary key in another entity. This allows related data to be looked up and found.
Asfia Rahman

13. Creating relationship on access
There should be a field in table B that is the Primary key of Table A
Table A
Table B
Asfia Rahman

14. One to one
A one-to-one relationship is when each record in one table only connects to one record in another table,
Each foreign key value will link to one primary key value and each primary key value will only be linked to by one foreign
The foreign key can exist on either side of the relationship
Sales rep
Employee
Club member
Exclusive member
Asfia Rahman

15. One to one in access Some rules to follow How to create:
At least one of the tables (table A) must have a PK.
The other table (table B) must either have
A PK that is also a FK and will link to the PK in table A.
Or a FK with unique index that will link to PK in table A
Data type and filed size of FK in B and PK in A must match.
Only data items that exist in PK in A can be used in FK in B
How to create:
Both of the common fields (typically the primary key and foreign key fields) must have a unique index.
This means that the Indexed property for these fields should be set to Yes (No Duplicates). (very important step!)
If both fields have a unique index, Access creates a one-to-one relationship.
Asfia Rahman

16. Click and drag the PK to FK.
Step 2:
Click and drag the PK to FK.
Make sure to CHECK “referential integrity
Step 1: Make sure that foreign ley filed is indexed to NO DUPLICATES
Asfia Rahman

17. One to many
When each record in one table can connect to many (zero or more) records in another table
FK will exist within the table on many side of relationship. It will connect to PK in the one side of relationship.
Table A PK
(one side)
Table B FK
(many side)
Asfia Rahman

18. One to many in access
When creating a one-to-many relationship, there are some rules to follow:
the table on the one side must have a primary key
the table on the many side will have a foreign key
the data type and field size of the foreign key must match the primary key on the one side
only data items that exist in the primary key on the one side can be used in the foreign key.
Asfia Rahman

19. Step 1: Make sure that FK field has same data type and field size as the PK
Asfia Rahman

20. Step 2: Click on PK on one side and drag it to FK field on many side.
Make to select “enforce referential integrity”
Asfia Rahman

21. many to many Many-to-many relationships are only conceptual.
They are not used in relational databases because they are converted into two sets of one-to-many relationships.
In a many-to-many relationship, each record in one table can connect to many records in another table but each record in the other table can also connect to many records in the original table.
Table A
Table B
Asfia Rahman

22. example
The Order table stores data about the orders that are placed including which products are being sold. It has a field called Product IDs which lists the products being sold on each order. Each order can have many products. Each product can exist on many orders. There are many Orders to many Products.
Asfia Rahman

23. many to many in access
It is necessary to break M-M into 1-M relationship
The rule is to put a LINK table between the two entities.
A new PK is created in the LINK table.
The primary keys for each of original tables are used as FKs in the LINK table
Asfia Rahman

24. One to many task
Asfia Rahman

25. Many to many questions
Resolve the following many-to-many relationships and suggest attribute names for all three tables:
many Orders to many Products
many Hire Car to many Drivers
many Authors to many Books
many Students to many Classes
many Employees to many Skills
many Doctors to many Patients
Asfia Rahman

26. Referential integrity
Exists when data in the foreign key of the table on the many side of a relationship exists in the PK of the table on the one side of a relationship
Without referential integrity a relationship cannot be properly set within a database.
It is a type of lookup validation where the database will check to see if the related record exists before allowing it to be entered.
If the related record does not exist, then the database will prevent the foreign key data from being entered.
This is important for maintaining the accuracy of the data within the database.
If details of which classes you attend were entered into a database, but those classes did not exist, then the database would not be able to give you any information about the classes
Asfia Rahman

27. tasks CD 9.10 Sales processing 3.mdb
Open CD 9.10 Sales processing 3.mdb
Open the order table and add Sales Rep IDs 4, 5, 8, 11 and 15 to the records.
Which ones worked?
Which ones did not work?
Why didn't they work?
Try to create a relationship between Product and Category and enforce referential integrity.
What happens?
Why has this happened?
Correct any data that is causing this problem and try to create the relationship again.
Asfia Rahman

28. Asfia Rahman

29. Asfia Rahman

30. Asfia Rahman

31. Asfia Rahman

32. Asfia Rahman

33. Asfia Rahman

34. Asfia Rahman

35. Asfia Rahman

36. Asfia Rahman

37. Asfia Rahman

38. Asfia Rahman

39. Asfia Rahman

40. Asfia Rahman

41. Asfia Rahman