by David Siguelnitzky, MIS; MTE

Lecture 2 - Version 1.1.0

Data Model

The Importance of Data Models

     • Data model

          – Relatively simple representation, usually graphical, of complex real-world data structures

          – Communications tool to facilitate interaction among the designer, the applications programmer, and the end user

     • Good database design uses an appropriate data model as its foundation

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

             • Must brief, precise, and unambiguous description of a policy, procedure, or principle within a specific organization’s environment

             • Apply to any organization that stores and uses data to generate information

             • Describe operations that help to create and enforce actions within that organization’s environment

             • Must be rendered in writing

             • Must be kept up to date

             • Sometimes are external to the organization (e.g.: army)

             • 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

        Importance of Business Rules

             • Promote creation of an accurate data model

             • Standardize company’s view of data

             • Constitute a communications tool between users and designers

             • Allow designer to understand the nature, role, and scope of data

             • Allow designer to understand business processes

             • Allow designer to develop appropriate relationship participation rules and constraints

        The Evolution of Data Models

             • Hierarchical

             • Network

             • Relational

             • Entity relationship

             • Object oriented

        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

        The Hierarchical Model

             • Advantages

                  – Conceptual simplicity

                  – Database security & integrity

                  – Data independence

                  – Efficiency

             • Disadvantages

                  – Complex implementation (limitations)

                  – Difficult to manage

                  – Complex applications programming and use

                  – Lack of standards

        The Network Model

             • Created to

                  – Represent complex data relationships more effectively

                  – Improve database performance & standards

             • Ruled by:

                  – Conference on Data Systems Languages (CODASYL)

                  – American National Standards Institute (ANSI)

                  – Database Task Group (DBTG)

        Crucial Database Components

             • Schema

                  – Conceptual organization of entire database as viewed by the database administrator

             • Subschema

                  – Defines database portion “seen” by the application programs that actually produce the desired information from data contained within the
                    database

             • Data Management Language (DML)

                  – Define data characteristics and data structure in order to manipulate the data

        Data Management Language Components

             • Schema Data Definition Language (DDL)

                  – Enables database administrator to define schema components

             • Subschema DDL

                  – Allows application programs to define database components that will be used

             • DML

                 – Manipulates database contents

        Network Model—Basic Structure

             • Resembles hierarchical model

             • Collection of records in 1:M relationships

             • Set

                  – Relationship between the components

                  – Composed of at least two record types

                       • Owner

                            – Equivalent to the hierarchical model’s parent

                       • Member

                            – Equivalent to the hierarchical model’s child

        The Relational Model

             • Developed by Codd (IBM) in 1970

             • Considered ingenious but impractical in 1970

             • Conceptually simple

             • Computers lacked power to implement the relational model

             • Today, microcomputers can run sophisticated relational database software

        The Relational Model—Basic Structure

             • Name: Relational Database Management System (RDBMS)

             • Performs same basic functions provided by hierarchical and network DBMS systems, plus other functions

             • Most important advantage of the RDBMS is its ability to let the user/designer operate in a human logical environment

             • Table (relations)

                  – Matrix consisting of a series of row/column intersections

                  – Related to each other by sharing a common entity characteristic

             • Relational schema

                  – Visual representation of relational database’s entities, attributes within those entities, and relationships between those entities

        Relational Table

             • Stores a collection of related entities

                  – Resembles a file

             • Relational table is purely logical structure

                  – How data are physically stored in the database is of no concern to the user or the designer

                  – This property became the source of a real database revolution

        The Entity Relationship Model - Basic Structure

             • Entity relationship diagram (ERD)

                  – Uses graphic representations to model database components

                  – Entity is mapped to a relational table

             • Entity instance (or occurrence) is row in table

             • Entity set is collection of like entities

             • Connectivity labels types of relationships

                  – Diamond connected to related entities through a relationship line (See Figure 2.6)

        The Object Oriented Model

             • Semantic data model (SDM) developed by Hammer and McLeod in 1981

             • Modeled both data and their relationships in a single structure known as an object

             • Basis of object oriented data model (OODM)

             • OODM becomes the basis for the object oriented database management system (OODBMS)

             • Object is described by its factual content

                  – Like relational model’s entity

             • Includes information about relationships between facts within object and relationships with other objects

                  – Unlike relational model’s entity

             • Subsequent OODM development allowed an object to also contain operations

             • Object becomes basic building block for autonomous structures

        Object Oriented Data Model - Basic Structure

             • Object: abstraction of a real-world entity

             • Attributes describe the properties of an object

             • Objects that share similar characteristics are grouped in classes

             • Classes are organized in a class hierarchy

             • Inheritance is the ability of an object within the class hierarchy to inherit the attributes and methods of classes above it

        The Object Oriented Model

             • Advantages

                  – Adds semantic content

                  – Visual presentation includes semantic content

                  – Database integrity

                  – Both structural and data independence


             • Disadvantages

                  – Complex navigational data access

                  – Steep learning curve

                  – High system overhead slows transactions

        Database Models and the Internet

             • Characteristics of successful “Internet age” databases

                  – Flexible, efficient, and secure Internet access that is easily used, developed, and supported

                  – Support for complex data types and relationships

                  – Seamless interfacing with multiple data sources and structures

                  – Relative conceptual simplicity to make database design and implementation less cumbersome

                  – An abundance of available database design, implementation, and application development tools

                  – A powerful DBMS graphical user interface (GUI) to help make the DBA’s job easier

             • American National Standards Institute/Standards Planning and Requirements Committee (ANSI/SPARC)

                  – Classified data models according to their degree of abstraction (1970s):

                       • Conceptual

                       • External

                       • Internal

        The Conceptual Model

             • Represents global view of the database

             • Enterprise-wide representation of data as viewed by high-level managers

             • Basis for identification and description of main data objects, avoiding details

             • Most widely used conceptual model is the entity relationship (E-R) model

        The Internal Model of E-R

             • Representation of the database as “seen” by the DBMS

             • Adapts the conceptual model to the DBMS

             • Software dependent

             • Hardware independent

        The External Model of E-R

             • End users’ view of the data environment

             • Requires that the modeler subdivide set of requirements and constraints into functional modules that can be examined within the framework of
               their external models

             • Good design should:

                  – Consider such relationships between views

                  – Provide programmers with a set of restrictions that govern common entities

Source: Rob and Coronel Database Systems: Design, Implementation and Management – 6th Edition Course Technology

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