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 –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 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.