Relational Database and Data Modeling Lecture 10 (Chapter 4)

Relational Database andData Modeling

Lecture 10(Chapter 4)

Lecture 10-2

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

Introduction This lecture explains what a database is and

how it differs from a file-oriented system. It describes the structure of a relational

database system & the basic steps involved in designing a database.

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Databases

For many years, companies created new files and programs each time an information need arose.

This proliferation of master files created problems:1 Often the same data was stored in two or

more separate files.2 The specific data values stored in the

different files were not always consistent.

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Databases

The database approach views data as an organizational resource that should be used by, and managed for, the entire organization, not just the originating department or function.

Its focus is data integration and data sharing.

Integration is achieved by combining master files into larger pools of data that can be accessed by many application programs.

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Types of Files

Two basic types of files are used to store data:1 The master file, which is conceptually

similar to a ledger in a manual system.2 The transaction file, which is

conceptually similar to a journal in a manual system.

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File-Oriented Approach

Applicationprogram #2


File # 1

Item A Item B Item C

File # 2

Item B Item D Item E

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Database Approach



Databasemanagement

system


Item A Item B Item C Item D Item E

Database

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Database Approach versus File-Oriented Approach

Minimum data redundancy

Fewer data inconsistencies

Standardized data format

No duplicated processing or storage

Allows cross-functional data analyses

Central data management / data security

Lower cost

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Databases

Database management system (DBMS) is the program that manages and controls access to the database.

Database system is the combination of the database, the DBMS, and the application program that uses the database.

Database administrator (DBA) is the person responsible for the database.

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Relational Databases

A data model is an abstract representation of the contents of a database.

The relational data model represents everything in the database as being stored in the form of tables.

Technically, these tables are called relations. Each row in a relation, called a tuple,

contains data about a specific occurrence of the type of entity represented by that table.

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Logical & Physical Views of Data

A major advantage of database systems over file-oriented systems is that the database systems separate the logical and physical view of data: Logical view: It is how the user or programmer conceptually

organizes and understands the data. Physical view: It refers to how and where the data are

physically arranged and stored on disk, tape, CD-ROM, or other media.

The DBMS controls the database so that users can access, query, or update it without reference to how or where the data are physically stored.

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Schemas

What are schemas? A schema describes the logical

structure of a database. There are three levels of schemas:

1 Conceptual-level schema2 External-level schema3 Internal-level schema

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Schemas

The conceptual-level schema is an organization-wide view of the entire database.

The external-level schema consists of a set of individual user views of portions of the database, also referred to as a subschema.

The internal-level schema provides a low-level view of the database.

Schema Levels:

1. Conceptual

2. External

3. Internal

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The Data Dictionary

What is a data dictionary?It contains information about the

structure of the database. For each data element stored in the

database, such as the customer number, there is a corresponding record in the data dictionary describing it.

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The Data Dictionary

The data dictionary is often one of the first applications of a newly implemented database system.

Inputs to the data dictionary:– records of any new or deleted data elements– changes in names, descriptions, or uses of existing

data elements

Outputs of the data dictionary:– reports useful to programmers, database designers,

and users of the information system

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DBMS Languages

Every DBMS must provide a means of performing the three basic functions:1 Creating the database2 Changing the database3 Querying the database

The sets of commands used to perform these functions are referred to as the data definition, data manipulation, and data query languages.

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DBMS Languages Data definition language (DDL):

– build the data dictionary.– initialize or create the database.– describe the logical views for each individual user or

programmer.– specify any limitations or constraints on security

imposed on database record or fields. Data manipulation language (DML):

– Data maintenance (updating / inserting / deleting) Data query language (DQL):

– Interrogate the database (retrieves / sorts / orders and and presents subsets of the database in response to user queries)

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Basic Requirements of the Relational Data Model

1 Primary keys must be unique.2 Every foreign key must either be null or have a

value corresponding to the value of a primary key in another relation.

3 Each column in a table must describe a characteristic of the object identified by the primary key.

4 Each column in a row must be single-valued.5 The value in every row of a specific column must

be of the same data type.6 Neither column order nor row order is significant.

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Database Design Objectives

Completeness Relevance Accessibility Up-to-dateness flexibility Efficiency Cost-effectiveness Integrity Security

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Approaches to Database Design Normalization

Starts with the assumption that all data is initially stored in a large non-normalized table.

This table is then decomposed using a set of normalization rules to create a set of tables in the Third Normal Form.

Semantic Data Modeling The database designer uses his/her

knowledge about the business structure to create a set of relational tables.

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Designing and Implementing a Database System

Six basic steps involved in designing and implementing a database system:

1. Initial planning to determine the need for and feasibility of developing a new system.

2. Identifying user needs.3. Developing the contextual-, external-and internal-level

schemas.4. Translating the internal-level schema into the actual

database structures that will be implemented in the new system.

5. Transferring all data from the existing system to the new database.

6. Using and maintaining the new system.

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The REA Data Model

Data modeling is the process of defining a database so that it represents all aspects of the organization, including its interactions with the external environment.

The REA data model is a conceptual modeling tool specifically designed to provide structure for designing AIS databases.

REA data model provides structure in two ways:1 By identifying what entities should be included in the AIS

database2 By prescribing how to structure relationships among the

entities in the AIS database

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End of Lecture 10

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Relational Database and Data Modeling Lecture 10 (Chapter 4)