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Lecture

COMPSCI 1BA3 Lecture Notes - Meridian Regional Airport, First Normal Form, Electrical Contacts


Department
Computer Science
Course Code
COMPSCI 1BA3
Professor
Dr.Hurst

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Access
Access is a relational DBMS:
Each access database can be 2GB, can have 32,768 objects and 255 people can use it at the same time
Field: single characteristic or attribute of a person, place, object, event or idea. Ex; customer ID, first name, last name
Content of a field is called a field value
The data type determines what field values you can enter for the field
Columns (fields)
Rows (records)
Table: collection of fields that describes as person, place, object or idea
A collection of related tables is called a database or relational database
You can connect the records in separate tables through a common field that appears in both tables
A primary key is a field, or a collection of fields, whose values uniquely identify each record in a table.
When you include the primary key from one table, as a field in a second table, to form a relationship between two
tables, it is called a foreign key.
Relational Database Management Systems
Database management system (DBMS): a software program that lets you create databases and then manipulate data in
them.
A relationship between two tables in a relational DBMS is formed through a common field
Most of today’s database management systems including access are called relational database management systems
(where data is organized as a collection of tables).
A Relational DBMS
Creates database structures containing fields, tables and table relationships
Lets you add new records, change field values in records and delete records
Built in query language lets you get answers to questions about your data
Protects through security, control and recovery facilities
Types of relationships among tables:
One to one, one to many, many to many (many to many is the most common)
Designing a relational database
Normalization: a process used by designers to eliminate undesirable anomalies that occur during the management of a
database.
A way to make large tables into smaller related tables
1NF (no multi-valued attributes), 3NF (minimal normal form necessary for a working database design)
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Overall database design is known as “schema”, views are “sub-schemas”
* Access uses the term “view” in a very different manner* [Datasheet View, Design View are not sub-schemas]
Special Considerations
Sharing and Security
o Isolation: DBA can create VIEWS for individual/groups, to protect sensitive data
o Locking Shared Data: readers and writers
o Protection: passwords, time controls, capability controls. Monitoring
o Recovery: backup, transaction logging, checkpoints
Real-Time Operation
o Serialization: sequencing of operations, time-stamping of transactions
Creating a Simple Query
A query can be a question you “ask” about the data stored in the database
o (saved as objects)
A Simple Query wizard is used to quickly select records and fields to form a question
Not entered in natural language (SQL, QBE, Wizard, Report)
SQL structured query language, international standard for database manipulation
Only the query DESIGN is saved as an object
Creating a Simple Form
A form is an object you use to enter, edit, and view records in a database
Creating a Simple Report
A report is a formatted printout (screen shot) of the content of one or more tables in a database
Compacting and Repairing a Database
Compacting a database rearranges database objects and data to decrease the file size
Building a Database and Defining Table Relationships
Description Property: use it enter an optional description for a field to explain its purpose. (up to 255 characters)
Field Size Property: defines a field value’s maximum storage size for TEXT, NUMBER & AUTONUMBER fields ONLY
GUIDELINES FOR DESIGNING DATABASES
Identify all the fields needed to produce the required information
Organize each piece of data into its smallest useful part
Group related fields into tables
RECALL: Primary key uniquely identifies records in a table
For some tables; one of the fields serves as the primary key
For other tables; two or more fields might be needed to be served as a primary key
o In these cases, the primary key is called the composite key
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