Eugenius Kuncoro


Posted: October 1st 2012

Basic of Data Arrangement &Access

Data hierarchy : Database contains files,file contains records, record contain fields, field contains charracters.
Recall…8bits->1byte=>1 char
Field (field size, field name, data type): a logical grouping of characters into a word, a small group of words, or a complete number.
Record : a logical grouping of related fields.
File : a logical grouping of related records.
Database : a logical grouping of related files.

Data Management Terminology
Entity : a person, a place, thing, or event about which information is maintained. (Records) describe entities.
Attribute : each characteristic or quality describing a particular entity.(Fields) describe attribute.
Primary Key : field that uniquely identifies the record.
Secondary Key : field doesn’t identify the records uniquely, but can be used to form logical groups of records.

Locating Data in Database
Centralized  :

  •  All the related files are in one physical location
  • Data consistency is improved and security is easier
  • Recover from disaster is easier
  • Vulnerable to a single point failure
  • Speed problem due to transmission delays.

Distributed : complete copies of a database, or porpotions of a database, are in more than one location, close to the user.
Type 1(Replicated Database) :

  • copies of database in many locations.
  • reduced single point of failure problems.
  • increased user access responsiveness.

Type 2(Partitioned Database) :

  • a portion of database in each location.
  • each location responsible for its own data.

Database Management System
A set of software programs that provide access to database.

DBMS components :
Data model : defines the way data are conceptually structured.
Data definition language : used to define the content and structure of the database, user define their logical view(schema) of the database using the DDL, relationship, primary key, and secure can be established.
Data Manipulation Language : used to query the contents of the database, store or update information in the database, and develop database applications.
Data Dictionary : stores definitions of data elements and data characteristics. 

DBMS benefits :

  • improved strategic use of corporate data.
  • reduced complexity of IS environment
  • reduced data redundancy and inconsistency
  • enhanced data itegrity
  • application indepedence
  • improved secutiy
  • improved IS flexibility
  • increased data access


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