Data Modeling in Database Systems: Classification, Evolution, and Comparison, Thesis of Marketing

Download Data Modeling in Database Systems: Classification, Evolution, and Comparison and more Thesis Marketing in PDF only on Docsity!

Chapter 2

Data Model

Database Systems:

Design, Implementation, and Management, Sixth

Edition, Rob and Coronel

In this chapter, you will learn:  Why data models are important  About the basic data-modeling building blocks  (^) What business rules are and how they affect database design  (^) How the major data models evolved, and their advantages and disadvantages  (^) How data models can be classified by level of abstraction

Importance of Data Modeling  End-users have different views and needs for data  (^) Data model organizes data for various users

Data Model Basic Building Blocks  (^) Entity is anything about which data are to be collected and stored  (^) Attribute is a characteristic of an entity  (^) Relationship describes an association among (two or more) entities  (^) One-to-many (1:M) relationship  Many-to-many (M:N or M:M) relationship  One-to-one (1:1) relationship

Business Rules (continued)  Must be rendered in writing  (^) Must be kept up to date  (^) Sometimes are external to the organization  (^) Must be easy to understand and widely disseminated  (^) Describe characteristics of the data as viewed by the company

Sources of Business Rules  (^) Company managers  (^) Policy makers  (^) Department managers  (^) Written documentation  (^) Procedures  (^) Standards  Operations manuals  (^) Direct interviews with end users

The Evolution of Data Models  Hierarchical  (^) Network  Relational  (^) Entity relationship  (^) Object oriented

Evolution of Major Data Models

The Hierarchical Model—Evolution  (^) GUAM (Generalized Update Access Method)  (^) Based on the recognition that the many smaller parts would come together as components of still larger components  (^) In the mid 1960s. IBM joined Rockwell to expand the capabilities of GUAM, replacing computer tapes with disk storage  (^) Information Management System (IMS)  (^) The result of the joint effort between Rockwell and IBM  (^) World’s leading mainframe hierarchical database system in the 1970s and early 1980s

The Hierarchical Model— Characteristics  (^) Basic concepts form the basis for subsequent database development  (^) Limitations lead to a different way of looking at database design  (^) Basic concepts show up in current data models  (^) Best understood by examining manufacturing process

Hierarchical Structure—Characteristics  (^) Each parent can have many children  (^) Each child has only one parent  (^) Tree is defined by path that traces parent segments to child segments, beginning from the left  (^) Hierarchical path  (^) Ordered sequencing of segments tracing hierarchical structure  (^) Preorder traversal or hierarchic sequence  (^) “Left-list” path  (^) If Part D is most frequently accessed and updated, change the database structure to place Part D closer to the left side of the tree  (^) This will give a shorter traversal

The Hierarchical Model  (^) Advantages over a file system  (^) Conceptual simplicity – easy to understand the model layout  (^) Database security  (^) Data independence (a change in a data type will be automatically cascaded throughout the database by the DBMS, thereby eliminating the need to make changes in the program segments that reference the changes data type)  (^) Database integrity – always a link between parent and child  (^) Efficiency – very efficient when it contains a large volume of data in 1:M relationships and whose relationships are fixed over time

Child with Multiple Parents

The Network Model  (^) Created to  (^) Represent complex data relationships more effectively  Improve database performance  Impose a database standard  (^) Conference on Data Systems Languages (CODASYL)  (^) American National Standards Institute (ANSI)  (^) Database Task Group (DBTG)