Transcript ch. 6 - AD Book Enterprises

2/20: Ch. 6 Data Management
• What is data?
• How is it stored?
– Traditional management storage
techniques; problems
– DBMS
What is data? The Data Hierarchy
• BIT: binary digit (0,1; Y,n; On,off)
• BYTE: combination of BITS which represent a
CHARACTER
• FIELD: collection of BYTES which represent a
DATUM or fact
• RECORD: collection of FIELDS which reflect a
TRANSACTION
• FILE: A collection of similar RECORDS
• DATABASE: an organization’s electronic library
of FILES
How is data stored?
• ENTITY: person, place, thing, event about which
data must be kept
• ATTRIBUTE: description of a particular
ENTITY
• KEY FIELD: field used to
retrieve, update, or sort
RECORD
How is Data Stored? The Key Field
• Field in each record that uniquely identifies a record for
– Retrieval
– Updating
– Sorting
How is data stored? File Organization
• Sequential
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Tape oriented
One file follows another
Follows physical sequence
ISAM: Indexed Sequential
Access Method
• Index tracks key fields, where
each record is stored.
• Speeds up access to records
How is data stored? File Organization
• Direct (or Random)
– Disk oriented
– Can be accessed without regard to physical sequence
– Transform algorithm
• Translates the key field into the physical location on disk.
So What’s the Problem? History
• Traditional management
storage techniques
• Each application was created
independently
– Each application had its own
database created
– Applications cannot share data
• Duplicate data exists across the
organization
• Inefficiency & Independence
reign supreme
What’s the Problem?
• Data Redundancy
– “Duplicate data exists across the organization”
• Program-Data Dependence
– “Each application had its own database created”
• Lack of Flexibility & Data-Sharing
– Too expensive to mine the data for undiscovered
relationships or information
• Poor security
– Who knows how many places your SSN is stored?
The Database
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Organization’s electronic library
Stores & manages data in a convenient form
Database Management System
• Software to create & maintain data
• Enables business applications to extract data
• Independent of specific computer programs
The 3 Key Components of a DBMS
• Data definition language:
– Defines data elements in database
• Data manipulation language:
– Manipulates data for applications
– SQL: Structured Query Language
• Emerging standard data manipulation language for
relational databases
• Data dictionary:
– Formal definitions of all variables in database;
Controls variety of database contents
So What’s the Big Deal?
• The DBMS separates the physical location and
conceptual (or logical) location of data in the file system.
• You don’t have to know where the data is to access or
manipulate it.
• PHYSICAL VIEW: where is data physically?
– Drive, disk, surface, track, sector, record
– Tape, block, record number (key)
• LOGICAL VIEW: what data is needed by application?
– Succession of facts needed by application
– Name, type, length of field
Next Time:
• Guest speaker: Jeff Till, programmer
• Using MS Excel
• Pick up database concepts again after Midterm
Exam.