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Transcript
CHAPTER 8:
MANAGING DATA
RESOURCES
File Organization Terms
• Field: group of characters that represent
something
• Record: group of related fields
• File: group of related records
• Database: group of related files
• Entity: a person, place, thing, event
• Attribute: a piece of information about
an entity
Entities, Attributes & Key Fields
Traditional File Processing
• Each functional area has specialized applications
• Each application requires an unique data file, that is often a
subset of the master file
PROBLEMS WITH TRADITIONAL FILE PROCESSING
• Data integrity
• Data redundancy and confusion
• Program-data dependence
• Lack of flexibility
• Poor security
• Lack of data sharing and availability
The Database Approach
• Database
– Collection of data organized to serve many
applications efficiently
– Data is centralized
– Uses a database management system (DBMS)
• Software to create and maintain a database
• Allows individual business applications to extract and
use the data they require
Logical and Physical Views
• Physical view
– How data are organized and stored on physical media
• Logical View
– How the data appear to an application programmer or end
user
– Could be multiple logical views
• DBMS allows logical and physical views to be
separated
Three components of DBMS
1. Data definition language
•
•
Defines each data element
Used by programmers in creating database
2. Data manipulation language
•
Used to manipulate data (e.g. SQL)
3. Data dictionary
•
Stores and organizes information about the
data
Types of Relations
ONE-TO-ONE:
ONE-TO-MANY:
MANY-TO-MANY:
STUDENT
ID
Department --> Faculty Member
CLASS
1
STUDENT
A
CLASS
2
STUDENT
B
STUDENT
C
Types of Databases
• Hierarchical DBMS
– Older model
– Treelike structure, one-to-many relationships
• Network DBMS
– Also older model, allows many-to-many
relationships
• Neither are as flexible nor as easy to use as
relational DBMS
Relational DBMS
Tables share a
common
data element
Basic Operations of Relational
DBMS
• Select
– Creates a subset of records that meet criteria
– E.g. all records (rows) with part number = 137
• Project
– Creates a subset of columns
– Allows user to create new tables, or views, of data
• Join
– Allows user to combine tables
– E.g. table of parts + supplier
Querying Databases: SQL
• SELECT
– Lists the columns from tables that the user wants to see in the
result
• FROM
– Identifies the tables from which the columns will be selected
• WHERE
– Includes conditions for selecting specific rows (records)
Designing Databases
Entity-relationship diagram
– A methodology for
documenting databases
– Illustrates relationships
between entities
– Relationship can be
• One-to-many
• One-to-one
• Many-to-many
Normalization
Eliminates redundant data and awkward relationships
Unnormalized relation for ORDER
Normalized relation for ORDER
Distributed Databases
• A database can be stored at more than one location
• Parts or copies are physically stored in different
locations
Management Requirements
• Data Administration
• Data Planning and Modeling
• DataBase Administration
Data Warehouses & Datamining
• Extracts current & historical data from operational
systems
• Combined with external data
• Create database for analysis by management
• Usually read only
Databases and the Web