Page 155 - DMGT505_MANAGEMENT_INFORMATION_SYSTEM

Management Information Systems

Notes which facilitate fast retrieval of data from large tables. Any column can be a key, or multiple
columns can be grouped together into a compound key. It is not necessary to define all the keys
in advance; a column can be used as a key even if it was not originally intended to be one.
A key that has an external, real-world meaning (such as a person’s name, a book’s ISBN, or a car’s
serial number) is sometimes called a “natural” key. If no natural key is suitable (think of the
many people named Brown), an arbitrary or surrogate key can be assigned (such as by giving
employees ID numbers). In practice, most databases have both generated and natural keys,
because generated keys can be used internally to create links between rows that cannot break,
while natural keys can be used, less reliably, for searches and for integration with other databases.

Example: Records in two independently developed databases could be matched up by
social security number, except when the social security numbers are incorrect, missing, or have
changed.

The basic structure of the relational model is as follows:
1. RDBMS allows operations in a human logical environment
2. The relational database is perceived as a collection of tables
3. Each table consists of a series of row/column intersections
4. Tables (or relations) are related to each other by sharing a common entity characteristic
(called a key)
5. The relationship type is often shown in a relational schema
6. A table yields complete data & structural independence.

A visual representation of this model is shown below.

Table 8.1: Relational Model: Name - Student
Code Surname Name Street City Tutor Code
01 Vadodaria Reetesh Powai Mumbai 15
11 Jani Apurva Chandivali Mumbai 19
17 Patel Sameer Peddar Rd. Mumbai 02
25 Agrawal Umang Malad Mumbai 05
30 Bansal Shilpi Borivli Mumbai 22

Table 8.2: Link through Tutor Code: Name – Faculty

Tutor Code Surname Name Street City
02 Kumta Gita Goregaon Mumbai
05 Acharya Neeta Santacruz Mumbai
15 Agnihotri Prafulla Dindoshi Mumbai
19 Sirur Pratap Malabar Hill Mumbai
22 Sunder Ram K. Mira Rd. Mumbai

The advantages of the relational model are:

1. Structural independence
2. Improved conceptual simplicity

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