Java Reference
In-Depth Information
• Employee identification number (a whole number)
• Name (a string of characters)
• Address (a string of characters)
• Hourly pay rate (a number with a decimal point)
• Year-to-date earnings (a number with a decimal point)
• Amount of taxes withheld (a number with a decimal point)
Thus, a record is a group of related fields. In the preceding example, all the fields belong to
the
same
employee. A company might have many employees and a payroll record for each.
Files
A
file
is a group of related records. [
Note:
More generally, a file contains arbitrary data in
arbitrary formats. In some operating systems, a file is viewed simply as a
sequence
of bytes
—
any organization of the bytes in a file, such as organizing the data into records, is a view
created by the application programmer. You'll see how to do that in Chapter 15.] It's not
unusual for an organization to have many files, some containing billions, or even trillions,
of characters of information.
Database
A
database
is a collection of data organized for easy access and manipulation. The most
popular model is the
relational database
, in which data is stored in simple
tables
. A table
includes
records
and
fields
. For example, a table of students might include first name, last
name, major, year, student ID number and grade point average fields. The data for each
student is a record, and the individual pieces of information in each record are the fields.
You can
search
,
sort
and otherwise manipulate the data based on its relationship to multiple
tables or databases. For example, a university might use data from the student database in
combination with data from databases of courses, on-campus housing, meal plans, etc. We
discuss databases in Chapter 24.
Big Data
The amount of data being produced worldwide is enormous and growing quickly. Accord-
ing to IBM, approximately 2.5 quintillion bytes (2.5
exabytes
) of data are created daily and
90% of the world's data was created in just the past two years!
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According to a Digital Uni-
verse study, the global data supply reached 2.8
zettabytes
(equal to 2.8 trillion gigabytes)
in 2012.
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Figure 1.4 shows some common byte measurements.
Big data
applications deal
with such massive amounts of data and this field is growing quickly, creating lots of op-
portunity for software developers. According to a study by Gartner Group, over 4 million
IT jobs globally will support big data by by 2015.
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