Databases

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Databases
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Terms

• DBMS Database management system
• RDBMS Relational database management system
• Excel flat-file (single table)
• Access relational (many tables)
• Database a collection of related information
• To retrieve information
• To analyze information

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File management vs. database

• File management system or file manager
• Retrieves and manipulates files, one file at a
  time
• Database manager data elements are
  cross-referenced and shared. Data is stored in
  only one place. Change it there, all other files
  access it.

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File management systems
In the traditional file management system, some
of the same data elements, such as addresses,
were repeated in different files. Information
was not shared among files.
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Database management system
In the database management system, data elements
are integrated and shared among different files.
Information updated in one file will
automatically be updated in other files.
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Parts

• Table the primary object for collecting and
  storing data.
• Organized into columns and rows
• Fields (columns) hold a single piece of data
  should break it up into its smallest logical
  parts.
• Records (rows) individual entries in a table.

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Data Storage Hierarchy

• Byte a single character (letter A)
• Field a unit of data consisting of one or more
  characters (a single piece of data like last name
  or first name.)
• Record a collection of related fields (your
  name, address, phone number)
• File a collection of related records
• Database an organized collection of integrated
  files

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What is a field?

• Combination of one or more characters
• Smallest unit of data user accesses
• Field size defines the maximum number of
  characters a field can contain
• Field name uniquely identifies each field
• Data type specifies kind of data field contains

p. 10.05 Fig. 10-3
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What are common data types?

• What are common data types?

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What is a record?
Group of related fields

• What is a record?

Key field, or primary key, uniquely identifies
each record
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Key field

• A field that uniquely identifies a record so that
  it can be retrieved and processed.
• Customer or ID
• Social security
• Must be unique
• Called primary key in Access

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What is a data file?

• Collection of related records stored on disk

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• What is file maintenance?

• Procedures that keep data current

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• What is a query?

Step 1. Select the fields you want to display in
the resulting query.

• Request for specific data from a database
• Query language consists of simple, English-like
  statements that allow users to specify data to
  display, print, or store

Step 2. Assign a name to the query, so you can
open it later.
Step 3. View query on the screen.
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• What is a form?

• Window on screen that provides areas for entering
  or changing data in database

• Used to retrieve and maintain data in a database
• Form that sends data across network or Internet
  is called e-form, short for electronic form

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• What is a report generator?

• Allows user to design a report on screen,
  retrieve data into report design, then display or
  print reports

• Also called report writer

p. 10.18 Fig. 10-16
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Advantages of a DBMS

• DBMS Database Management system
• Reduced data redundancy (data is stored in only
  one place, not repeated in different files.)
• Improved data integrity (data is accurate,
  consistent and up-to-date) because data is
  updated in only once place

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Advantages of a DBMS

• Increased user productivity users can run
  reports and extract information without the help
  of programmers
• Increased security information can be limited by
  the use of passwords

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Disadvantages of DBMS

• Cost Installing and maintaining is expensive
  (training how to use properly is expensive)
• Security possible for unauthorized individuals
  to get past the safeguards
• Privacy issues databases may hold information
  that is used for unintended purposes

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Types of database organization

• Hierarchical databases
• Network databases
• Object-Oriented
• Relational
• Connects data in different files (tables) through
  the use of a key field or common data element

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Guidelines for Design

• Determine output requirements
• Determine input requirements
• Determine table structures
• Determine each tables primary key or unique
  identifier
• Determine the table relationships
• Test your database
• Avoid data redundancy

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90/10 Rule

• Place 90 of you effort in designing a database
  properly in order to spend 10 of your time
  maintaining it.