IT applications cannot be performed without
using data. Data should be accurate, complete. Timely, consistent, accessible, relevant,
and concise. There are several difficulties in Managing Data, Amount of data
increases exponentially, Data are scattered and collected by many individuals using
various methods and devices, Data come from many sources, and Data security,
quality and integrity are critical. An ever-increasing amount of data needs to
be considered in making organizational decisions Database management system
(DBMS) provides all users with access to all the data. DBMSs minimize several
problems, data redundancy which is the same data are stored in many places, data
isolation which is applications cannot access data associated with other
applications, and data inconsistency which is various copies of the data do not
agree. DBMSs
maximize the many issues like Data security which is Keeping the organization’s data safe from
theft, modification, and/or destruction, data integrity which is Data must meet
constraints (e.g., student grade point averages cannot be negative), and Data
independence which is Applications and data are independent of one another. Applications
and data are not linked to each other, meaning that applications are able to
access the same data.
Data
Hierarchy include, a bit which is a binary digit, or a “0” or a “1”, a byte which
is eight bits and represents a single character (e.g., a letter, number or
symbol), a field which is a group of logically related characters (e.g., a
word, small group of words, or identification number), a record which is a
group of logically related fields (e.g., student in a university database), afile
which is a group of logically related records, a database which is a group of
logically related files. Database designers plan the database design in a
process called entity-relationship (ER) modeling. ER diagrams consists of
entities, attributes and relationships. Entity
classes are groups of entities of a certain type. An instance of an entity
class is the representation of a particular entity. Entity instances have identifiers,
which are attributes that are unique to that entity instance.
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