Database Systems: Understanding Different Architectures and Objects, Slides of Fundamentals of E-Commerce

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Introduction to Databases

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Learning Objectives

• To describe a database
• Understand hierarchical, relational, and object- oriented databases
• Understand the process for developing a database system
• Create entity relationship models to describe a database design
• Derive database tables using an entity relationship model

Overview of Databases

• Data file approach to data processing

Overview of Databases (cont’d)

• In the case above (data file approach), each

application must have its own tools for:

• Inserting new data
• Viewing existing data
• Updating existing data
• Deleting existing data

Overview of Databases (cont’d)

Database Objects & Structures

• How do databases store data?
  • In data files
  • DBMS manages data files
  • DBMS enables users to perform basic data-handling procedures
• How should we organize data files?
  • Understand the structure of the database
  • Understand the database objects

Database Objects (cont’d)

• Attribute
  • Data value of an entity
  • Examples
    • StudentID
    • Firstname
• Relationship
  • Used to represent a connection among related entities, like a link

Database Objects (cont’d)

Database Structures

• Three primary database structures
  • Hierarchical databases
  • Relational databases
  • Object-Oriented databases
• Each structure stores data entity instance

values and represents relationships

differently

Hierarchical Databases

• Entities have parent-to-child relationship
• Uses pointers to create relationship between associated data items
• Pointer
  • Unique address value that defines the physical location of where data is stored on a storage device
  • Links data values of the parent entity instance with multiple child entity instances

Hierarchical Databases (cont’d)

• Problems with Hierarchical Databases
  • Difficult to move to new storage medium
    • Data is physically dependent on its location on the storage media
  • Changes to database structure require rewriting of programs - Time-consuming - Expensive

Relational Databases

Understand or memorize this info!

• Tables
  • Stores the data
• Records (like a row in a table)
  • Contains data about an individual entity instance
• Fields (table columns)
  • Attributes that are associated with individual data values
• Key fields
  • Create relationship among records in different tables

Relational Databases – Key Fields

• Primary key
  • Table field that uniquely identifies a record
  • Cannot be NULL
  • Mandatory for each table
• Surrogate key (SUK)
  • Fields that did not appear automatically (VIN or SIN) but were created by designers to be a designated primary key (e.g., student #, customer ID)
  • Unique, can be generated automatically for new records

Relational Databases – Key Fields

(cont’d)

• Foreign keys
  • Create a relationship between two tables
  • A primary key field in one table (parent) and acts as a foreign key in another table (child)
  • Enforces referential integrity
    • When a table is created with a foreign key, all foreign key values must exist in the parent table
    • Populate the table with primary keys first!!!