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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.