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311: Management Information Systems Database Systems Chapter 3

311: Management Information Systems Database Systems Chapter 3

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311: Management Information Systems

Database Systems

Chapter 3

© Jakob Iversen, 20022

Database

• Organized collection of related data– Databases: A list of phone numbers and

names. List of book titles and authors. List of customers and sales figures.

– Not databases: List of book titles and phone numbers. Pile of papers on a desk.

• Major Problems– Data are usually not collected in a very

organized fashion– Too much data – not enough information

© Jakob Iversen, 20023

The Data Hierarchy

© Jakob Iversen, 20024

Traditional File Environment

© Jakob Iversen, 20025

Problems with the File Approach

• data redundancy - the same piece of information could be duplicated in several places

• data inconsistency - the various copies of the data no longer agree

• data isolation - difficulty in accessing data from different applications

• data integrity - data values don’t adhere to integrity constraints

© Jakob Iversen, 20026

Database : The Modern Approach

• One database – several programs• Data changes only in one place• Examples: MS Access, Oracle, DB2

© Jakob Iversen, 20027

Advantages of Database Approach

• Reduced data redundancy

• Shared data and information resources

• Improved data integrity

• Easier modification and updating

• Data and program independence

• Better access to data and information

• Standardization of data access

• Framework for program development

• Better overall protection of the data

• Improved strategic use of corporate data

© Jakob Iversen, 20028

Disadvantages of Database Approach

© Jakob Iversen, 20029

• Data model– defines the way data are conceptually structured

• Data definition language (DDL)– defines what types of information are in the database and how they

will be structured– functions of the DDL

• provide a means for associating related data• indicate the unique identifiers (or keys) of the records• set up security access and change restrictions

• Data manipulation language (DML)– query the contents of the database, store or update information in

the database, and develop database applications– Structured query language (SQL) - most popular relational database

language, combining both DML and DDL features

• Data Dictionary (metadata)– stores definitions of data elements and data characteristics

DBMS Components

© Jakob Iversen, 200210

DBMS: Logical versus Physical View• Physical view

– Actual, physical arrangement and location of data

– Described in a schema (describes entire database)

• Logical view– represents data in a format that is

meaningful to a user and to the software programs that process that data

– Can be different for different users as described in subschemas

– Underlying structure may change but subschema (user view) remains the same

© Jakob Iversen, 200211

Use of Schemas and Subschemas

© Jakob Iversen, 200212

Database : Centralized database

• all related files in one location

• single mainframe computer

• Users can work on a database as a whole at one location

• files only accessible via the host computer

• disaster recovery can be more easily accomplished at a central location

• vulnerable to a single point of failure

• speed problem

© Jakob Iversen, 200213

Database : Distributed database

• complete copies (or portions) of a database, in more than one location

• replicated database - complete copies of entire database available at many locations: No single-point-of-failure and increased responsiveness

• partitioned database - a portion of the entire database in each location

• This is planned redundancy (p. 106)

© Jakob Iversen, 200214

Logical Data Models

• A manager’s ability to use a database is highly dependent on how the database is structured logically and physically.

• In logically structuring a database, businesses need to consider the characteristics of the data and how the data will be accessed.

• Three common data models: hierarchical, network, and relational

© Jakob Iversen, 200215

Hierarchical Model

• Fast access, large installed base• Best with one-to-many relationship btwn data• Cumbersome, redundant data

© Jakob Iversen, 200216

Network Model

• Related data ordered in sets• Member/owner of set• Can handle many-to-many relationships• How do we notify customers who ordered

a defective product?

© Jakob Iversen, 200217

Relational Model

• Tables– Files

• Tuples– Records

• Attributes– Fields

• Structured Query Language (SQL)– Query language

that simplifies access to data

– MS Access makes it even simpler!

SQL Example:SELECT (Customer_Name and Customer_Address) FROM Customer_Table WHERE Credit_Limit > 5000

© Jakob Iversen, 200218

The Entity Relationship ModelRelationship

Entity

Attribute Primary Key

© Jakob Iversen, 200219

Important Relational DB Concepts - 1

• Primary Key– Uniquely identifies records in a table– Examples: Employee ID, SSN, Account #– Can be more than one field– Must be defined in every table

• Foreign Key– Identifies a primary key in a different

table– This is how information is related

© Jakob Iversen, 200220

Important Relational DB Concepts - 2

• Redundant data– The same information exists in more

than one place in the database– Should be avoided– Only foreign keys should be

duplicated– Example

© Jakob Iversen, 200221

A Relational Database Model

• Identify for each table:– Records– Fields– Field values– Primary keys– Foreign keys

© Jakob Iversen, 200222

Queries can combine data

© Jakob Iversen, 200223

Problems with redundant data

© Jakob Iversen, 200224

Comparing Data Models

Model

Advantages Disadvantages

Hierarchi-cal

Speed and efficiency in search

Access to data is predefined by exclusively hierarchical relationships, predetermined by administrator. Limited search/ query flexibility. Not all data is naturally hierarchical.

Network Many more relationships between data elements can be defined. Greater speed and efficiency than relational database models.

The most complicated model to design, implement, and maintain. More flexibility than hierarchical model, but less than relational model.

Relational

Conceptual simplicity; no predefined relationships among data. High flexibility in ad hoc querying. New data and records can be added easily

Lower processing efficiency and speed. Data redundancy is common, requiring additional maintenance.

© Jakob Iversen, 200225

Worldwide Dabase Market Share, 2002

IBM36%

Oracle34%

Microsoft18%

NCR3%

Others9%

Total revenue: $6.6 billionSource: Gartner Dataquest

© Jakob Iversen, 200226

Selecting a DBMS

• Database Size• Number of

concurrent users• Performance• Integration

• Features• The Vendor• Cost

© Jakob Iversen, 200227

Data Warehousing

• Data extracted from production systems• Historical data for decision making• Concerns

– Data extraction (when, from where, what data)

– Data cleaning– Timeliness– Business mergers– Analysis: Data mining and Online Analytical

Processing (OLAP)

© Jakob Iversen, 200228

Data Warehouse Elements

© Jakob Iversen, 200229

Data Mart

• A data warehouse for single division or department

• Easier and cheaper to set up• More detailed data• But might create ’islands’ of

unlinked information

© Jakob Iversen, 200230

OLAP and Data Mining

© Jakob Iversen, 200231

Now what?

• Thursday– Lab, Access Tutorial 1– Lecture: Intro to lab and Access– Location: Halsey 101C– Due: IT Problem 1

• Next Tuesday– Catching up on Chapter 1 and 3