Chapter Eight

Managing Data Resources

File Organization and Concepts

The Data Hierarchy

Human Resources DatabasePersonnel Table

Database Payroll Table

TableJames Thompson 36 220 Larkin Drive Anna Harvey 24 63 Whalen Street

Record James Thompson 36 220 Larkin Drive

Field James Thompson (name field)

Byte 1011 10010

Bit 1, 0

File Organization Terms• Field - a grouping a characters into a word, a

group of words, or a complete number, such as a person’s name and age. (Key field - uniquely identifies)

• Record - A group of related fields.• File - a group of records of the same type• Entity -a person, place,thing, or event about which

information must be kept• Attribute - A piece of information describing a

particular entity.

Illustration of a Record

Entity = ORDERAttributes

Order Order Item Quantity AmountNumber Date Number

4340 2/8/99 1583 2 17.4 FIELDS

KEY FIELD

Accessing Records from Computer Files

• Sequential File Organization– a method of storing data records in which the

records must be retrieved in the same physical sequence in which they are stored

• Direct/Random File Organization– a method of storing data records in a file so that

they can be accessed in any sequence without regard to their actual physical order on the storage media

Data Access Methods

• Indexed Sequential Access Method– a file access method to directly access records organized

sequentially using an index of key fields

• Direct File Access Method- – a method of accessing records by mathematically

transforming the key fields into specific addresses for the records

• Transform Algorithm– a mathematical formula used to translate a record’s key field

directly into the record’s direct physical storage location

Indexed Sequential Access Method

Record230 Data

Cylinder IndexCylinder Highest Key

1 2002 3923 500. .. .

Track Index Track Index Track Index Cylinder 1 Cylinder 1 Cylinder 1Track # Highest Key Track # Highest Key Track # Highest Key

1 9 1 208 1 3992 19 2 238 2 4193 28 3 260 3 4404 39 4 279 4 468

Direct File Access Method

• Basically uses an algorithm within a disk stack to access the record

• Example - File Size -1000 records– take the prime number closet to the max

number of records (in this case 997), divide the key field number by this prime number and the remainder is the address location number.

A Disk StackAccessmechanism

10 Accessarms

11 disks

000 403

404 Tracks

20 Read/writeheads

20 Tracks

2 0 9 0 7 0 0 3

Track number

Read/write head number

Record number

A DASD AddressA DASD Address

Traditional File Environment

• A way of collecting and maintaining data in an organization that leads to each functional area or division creating its own data files and programs. Can be either flat or data approached.

• Problems with TFE– data redundancy, program data dependence,

inflexibility, poor data security, inability to share

SALES NO

112

128

153

159

162

166

NAME

ADAMS

WINKLER

HOUSE

FRANCIS

WILLIS

GROVETON

SALES NO

112

128

153

159

162

166

TERR

1

3

2

1

1

2

An Example of Two Flat FilesAn Example of Two Flat Files

Table A Table B

Problems with TFE Explained

• Data Redundancy– presence of duplicate data in multiple data files

• Program-Data Dependence – the close relationship between data and programs. Any update

in the data requires a format change within the software (ZIP/AREA CODE ex)

• Inflexibility - cannot produce custom reports• Security - with little control of data, hard to control

access• Data sharing - with data in many places hard to

share b/c you do not know where it is

The Database Concept• Database definition

An integrated collection of computer data, organized and stored in a manner that facilitates easy retrieval.

• Data independence -- keep data specifications separate from programs, in tables and indexes

Database Management System(DBMS)

• The special software to create and maintain a database and enable individual business applications to extract the data they need without having to create separate files or data definitions in their computer programs– a DBMS has three components– a data definition language– a data manipulation language– a data dictionary

Hierarchical Database

Custormers

Kathy Cindy Debra

Dog food

Cat food

Bird food

Dogfood

Bird food

.. ..

Customer

Order

Network Database

Custormers

Kathy Cindy Debra

Dog food

Cat food

Bird food

Dogfood

Bird food

.. ..

Customer

Order

Dog Food

Relational Database

• Table format• Easy access (query)

Customer(CustomerID, Name, OrderID,…)Order(OrderID, CustomerID, OrderDate,…)ItemsOrdered(OrderID, ItemID, Quantity)

CustomerCustomerID

Name

..

OrderOrderID

..…

ItemsOrderedOrderID

..

..

Database Differences

Comparison of Database AlternativesDB Type Processing Flexibility End-User Programming

Efficiency Friendliness ComplexityHierarchical high low low high

Network medium-high low-med low-moderate high

Relational low but high high lowimproving

Design a database

Sally’s Pet Store

Supplier

Employee

CustomerSale

Animal

The Pet store’s Database

Name AnimalID Category Breed Dateborn Gender Color

Cathy 123 Bird Lovebird 6/5/98 Male Yellow Terry 353 dog Canary 7/1/97 Female Red Sandy 345 dog African 8/5/98 Male Yellow Charles 232 Bird Parrot 4/6/99 Male Yellow Ruby 565 dog Other 6/4/99 Male Yellow Curtis 675 cat Grey 8/5/98 Male Grey

Employee Name Soc.Sec.No Address Salary AnimalIDDaniel 232423435 ….. $23000 123……… ……… ……

Animal

Structural Query Language (SQL)

• SELECT columns Which property do you want ?

• FROM tables What tables are involved?

• JOIN conditions How are the table joined?

• WHERE criteria What are the constraints?

Four basic commands:

SELECT AnimalID, Category, DatebornFROM AnimalWHERE ((Category=“Dog”) AND (Dateborn>#6/1/98#));

Query

Resulting table:AnimalID Category Dateborn

345 dog 8/5/98 565 dog 6/4/99 SELECT Name, AnimalID, Salary

FROM Employee

WHERE (AnimalID=#123#)

SQL(2)

• List all birds who are male or who are born before 6/1/98 and have red in their color

SELECT AnimalID, Category, Gender, Dateborn, Color

FROM Animal

WHERE (((Category=“Bird”) AND (Gender=“Male”))

OR ((Dateborn<#6/1/98#) AND

(Color Like “*Red*”)))

Back to Database Design

• The main idea is to separate all the 1 to many relationships.– Look at page 243, or to your access quiz for

examples

• Each table holds specific information that is tied to the other tables through ‘keys’ and relationships

• this process is referred to as normalization

Normalization

• Why?– To prevent anomalies - occurrences in the database

that result from inefficient database structure. They also cause harmful events that can change or erase data.

• There are three types of anomalies– insertion– deletion– modification

Insertion anomalies

• Refers to the inability to add data to the database because the tables are not referenced correctly.

• This is to say if we want to add a new element we would have to add to numerous tables, and failure to do so would cause inconsistent data.ex. The inability to enter a new employee w/o adding in multiple tables.

Deletion Anomalies

• This is the opposite of the insertion anomaly. When items are not referenced correctly we can lose information.

• Ex. We have an employee database that does not have a separate department database, if we delete that employee we will lose that dept. info.

Modification Anomalies

• This occurs when you can change the value of one of the attributes (columns) of a dept, but that data is not changed throughout the database, unless we go in and manually change each table.

Other Database Concepts

• Databases on the web– technology makes this really easy to do– the gsc example– makes for more efficient transfer of data as well

as collection, with db security we can have EDI which is the underlying foundation of Electronic Commerce

– related to Online Analytical Processing (OLAP) see book for example

Mgmt Requirements for DB Systems

• Data administration- this is the definition of information requirements and access– usually formulated into a information policy

• Data Planning and modeling - the actual database formation process, what are ‘keys’, attributes, and relationships

• database administration• users- the idea of making your database

useable by all employees, plus support

Database Administration

• Defines and organizes database structure and content

• develops security procedures to safeguard the database

• develops database documentation

• maintains the database mgmt. software

Other terms to look up and know

• Distributed database

• data warehouse

• datamart