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Lesson 2Hierarchical and relational databases
ObjectiveDescribe the characteristics of hierarchical and relational databases.

Hierarchical and Relational Databases

Hierarchical databases


Hierarchical databases are based on "parent/child" (or top-down) relationships among data elements. The logic in this arrangement is that a child may have only one "parent," but a "parent" may have more than one "child." Hierarchical databases are rigid, which makes them easy to maintain but difficult to query. Hierarchical databases have been used for core business applications such as payroll, accounts receivable, and accounts payable. The figure below shows how a simple order placed on a web site has to work its way down a hierarchical structure.

Hierarchical database: Order works its way down: 1) Billing, 2) Shipping, 3) Product Ordered, 4) Purchasing History
Hierarchical database: Order works its way down: 1) Billing, 2) Shipping, 3) Product Ordered, 4) Purchasing History

IBM's IMS (Information Management System) is one example of a proprietary hierarchical database software package.

Relational databases

Relational databases are based on the metaphor of a basic table with rows and columns. Data elements stored in these "tables" share a relationship defined by a common element, called a key. For example, the same product number (key) may be used by programs that process and ship orders, track inventory, update pricing, and so on.
The figure below illustrates how a product number (the key) entered by a customer on a Web site accesses many data sources simultaneously.
Relational database: Database based on the metaphor of a basic table with rows and columns. Data elements stored in these "tables" share a relationship defined by a common element called a key.



Relational database
Relational database: Tables in the relational database are related by means of a key
Examples of relational database products include:
  1. IBM DB2
  2. Informix SQL
  3. Microsoft SQL Server
  4. Oracle
In the next lesson, you will learn about the characteristics of database-driven Web sites.

Database Characteristics

Click the link below to increase your understanding of the differences between hierarchical[1] and relational databases.
Database Characteristics
[1]Hierarchical database: Database based on top-down relationships among data elements. Hierarchical databases are used for core business applications such as payroll and accounts receivable.