World Library  
Flag as Inappropriate
Email this Article

Hierarchical database model

Article Id: WHEBN0000247075
Reproduction Date:

Title: Hierarchical database model  
Author: World Heritage Encyclopedia
Language: English
Subject: Database, Relational database, Database model, Relational model, SNOMED CT
Collection: Database Models
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Hierarchical database model

Hierarchical model redirects here. For the statistics usage, see hierarchical linear modeling or hierarchical Bayesian model.

A hierarchical database model is a tree-like structure. The data is stored as records which are connected to one another through links. A record is a collection of fields, with each field containing only one value. The entity type of a record defines which fields the record contains.

Example of a hierarchical model

A record in the hierarchical database model corresponds to a row (or tuple) in the relational database model and an entity type corresponds to a table (or relation).

The hierarchical database model mandates that each child record has only one parent, whereas each parent record can have one or more child records. In order to retrieve data from a hierarchical database the whole tree needs to be traversed starting from the root node. This model is recognized as the first database model created by IBM in the 1960s.

Contents

  • History 1
  • Examples of hierarchical data represented as relational tables 2
  • See also 3
  • References 4
  • External links 5

History

The hierarchical structure was developed by IBM in the 1960s, and used in early mainframe DBMS. Records' relationships form a treelike model. This structure is simple but inflexible because the relationship is confined to a one-to-many relationship. The IBM Information Management System (IMS) and the RDM Mobile are examples of a hierarchical database system with multiple hierarchies over the same data. RDM Mobile is a newly designed embedded database for a mobile computer system.

The hierarchical data model lost traction as XML in the late 1990s[2] (see also XML database). The hierarchical structure is used primarily today for storing geographic information and file systems.

Currently hierarchical databases are still widely used especially in applications that require very high performance and availability such as banking and telecommunications. One of the most widely used commercial hierarchical databases is IMS.[3] Another example of the use of hierarchical databases is Windows Registry in the Microsoft Windows operating systems.[4]

Examples of hierarchical data represented as relational tables

An organization could store employee information in a table that contains attributes/columns such as employee number, first name, last name, and department number. The organization provides each employee with computer hardware as needed, but computer equipment may only be used by the employee to which it is assigned. The organization could store the computer hardware information in a separate table that includes each part's serial number, type, and the employee that uses it. The tables might look like this:

employeetable
EmpNo First Name Last Name Dept. Num
100 Ram Prathap 10-L
101 Ravi Kumar 10-L
102 Ramesh Naidu 20-B
103 sarath yadav 20-B
computertable
Serial Num Type User EmpNo
3009734-4 Computer 100
3-23-283742 Monitor 100
2-22-723423 Monitor 100
232342 Printer 100

In this model, the employee data table represents the "parent" part of the hierarchy, while the computer table represents the "child" part of the hierarchy. In contrast to tree structures usually found in computer software algorithms, in this model the children point to the parents. As shown, each employee may possess several pieces of computer equipment, but each individual piece of computer equipment may have only one employee owner.

Consider the following structure:

EmpNo Designation ReportsTo
10 Director
20 Senior Manager 10
30 Typist 20
40 Programmer 20

In this, the "child" is the same type as the "parent". The hierarchy stating EmpNo 10 is boss of 20, and 30 and 40 each report to 20 is represented by the "ReportsTo" column. In Relational database terms, the ReportsTo column is a foreign key referencing the EmpNo column. If the "child" data type were different, it would be in a different table, but there would still be a foreign key referencing the EmpNo column of the employees table.

This simple model is commonly known as the adjacency list model, and was introduced by Dr. Edgar F. Codd after initial criticisms surfaced that the relational model could not model hierarchical data.

See also

References

  1. ^ Michael J. Kamfonas/Recursive Hierarchies: The Relational Taboo!--The Relation Journal, October/November 1992
  2. ^ [3]
  3. ^ IBM Information Management System
  4. ^ [4]

External links

  • Troels' links to Hierarchical data in RDBMSs
  • Managing Hierarchical Data in MySQL (This page is from archive.org as the page has been removed from MySQL.com)
  • Hierarchical data in MySQL: parents and children in one query
  • Create Hierarchy Chart from Hierarchical Database
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.