Page 160 - DMGT505_MANAGEMENT_INFORMATION_SYSTEM

Unit 8: Databases and Data Warehouses

(b) Network Notes
(c) Relational
(d) Object-oriented
(e) Semi-structured

Before we move on to the study of the common data models, let us understand the concepts of
data relationships. Two pieces of data may have any of the following three relationships:
1. One-to-one (1:1): for example, each store-is managed by a single employee & each store
manager (employee) only manages a single store, i.e., employee (1) manages store (1).
2. One-to-many (1:M): for example, a painter paints many different paintings but each one
of them is painted by only that painter, i.e., painter (1) paints painting (M).
3. Many-to-many (M:N): for example, an employee may learn many job skills & each job
skill might me learned by many employees, i.e., employee (M) learns skill (N).

8.3.5 Hierarchical Model

In 1966, IBM released the first commercially available DBMS - IMS (Information Management
System) based on the hierarchical data model. The basic structure of this model is:
1. Collection of records is logically organized to conform to the upside-down tree (hierarchical)
structure.
2. The top layer is perceived as the parent of the segment directly beneath it.
3. The segments below other segments are the children of the segment above them.

4. A tree structure is represented as a hierarchical path on the computer’s storage media.
The following diagram shows the organization of a hierarchical DBMS.

Organization of a Hierarchical DBMS

Figure 8.6

Final assembly

Root segment (Filing cabinet)

Level 1 segment
(root children) Component A Component B Component C

Level 2 segment
Assembly A Assembly B Assembly C
(level 1 children)
Level 3 segment
Part A Part B Part C Part D Part E
(level 2 children)
The major advantages of this model are:

1. Conceptual simplicity
2. Database security
3. Data independence

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