in the world can be described or represented in one of two forms: analog or digital.
The principal feature of analog representations is that they are continuous. In
contrast, digital representations consist of values measured at discrete intervals.
watches are called digital because they go from one value to the next without
displaying all intermediate values. Consequently, they can display only a finite
number of times of the day. In contrast, watches with hands are analog, because
the hands move continuously around the clock face. As the minute hand goes around,
it not only touches the numbers 1 through 12, but also the infinite number of
points in between.
attempts at building computers used analog techniques, but accuracy and reliability
were not good enough. Today, almost all computers are digital.
(1) A characteristic. In a word processing application, an underlined word would
be said to have the underline attribute. In database systems, a field can have
various attributes. For example, if it contains numeric data, it has the numeric
In database management systems, the term attribute is sometimes used as a synonym
In DOS systems, every file has a file attributes that indicate several properties
of the file. For example, they indicate whether the file is read-only, whether
it needs to be backed up, and whether it is visible or hidden.
Short for bit error rate. In a digital transmission, BER is the percentage of
bits with errors divided by the total number of bits that have been transmitted,
received or processed over a given time period. The rate is typically expressed
as 10 to the negative power. For example, four erroneous bits out of 100,000 bits
transmitted would be expressed as 4 x 10-5, or the expression 3 x 10-6 would indicate
that three bits were in error out of 1,000,000 transmitted. BER is the digital
equivalent to signal-to-noise ratio in an analog system.
Short for bit error rate test, or tester, a procedure or device that measures
the bit error rate of a transmission.
Short for binary large object, a collection of binary data stored as a single
entity in a database management systems (DBMS). BLOBs are used primarily to hold
multimedia objects such as images, videos, and sound, though they can also be
used to store programs or even fragments of code. Not all DBMSs support BLOBs.
Acronym for bridge protocol data unit. BPDUs are data messages that are exchanged
across the switches within an extended LAN that uses a spanning tree protocol
topology. BPDU packets contain information on ports, addresses, priorities and
costs and ensure that the data ends up where it was intended to go. BPDU messages
are exchanged across bridges to detect loops in a network topology. The loops
are then removed by shutting down selected bridge interfaces and placing redundant
switch ports in a backup, or blocked, state.
In database systems, browse means to view data. Many database systems support
a special browse mode , in which you can flip through fields and records quickly.
Usually, you cannot modify data while you are in browse mode.
(n) A set of bits, bytes or characters grouped together for transmission.
An intermittent asynchronous transmission of a specific amount of data. Contrast
A data format in which each piece of data is separated by a comma. This is a popular
format for transferring data from one application to another, because most database
systems are able to import and export comma-delimited data.
A special, non-printing character. The ASCII character set defines
32 control characters, as shown in the table. Originally, these codes were designed
to control teletype machines. Now, however, they are often used to control display
monitors, printers, and other modern devices.
To change data from one format to another.
Refers to data that has been damaged in some way.
(1) Distinct pieces of information, usually formatted in a special way. All software
is divided into two general categories: data and programs. Programs are collections
of instructions for manipulating data.
can exist in a variety of forms -- as numbers or text on pieces of paper, as bits
and bytes stored in electronic memory, or as facts stored in a person's mind.
speaking, data is the plural of datum, a single piece of information. In practice,
however, people use data as both the singular and plural form of the word.
The term data is often used to distinguish binary machine-readable information
from textual human-readable information. For example, some applications make a
distinction between data files (files that contain binary data) and text files
(files that contain ASCII data).
In database management systems, data files are the files that store the database
information, whereas other files, such as index files and data dictionaries, store
administrative information, known as metadata.
database management systems, a file that defines the basic organization of a database.
A data dictionary contains a list of all files in the database, the number of
records in each file, and the names and types of each field. Most database management
systems keep the data dictionary hidden from users to prevent them from accidentally
destroying its contents.
dictionaries do not contain any actual data from the database, only bookkeeping
information for managing it. Without a data dictionary, however, a database management
system cannot access data from the database.
The process of entering data into a computerized database or spreadsheet.
Data entry can be performed by an individual typing at a keyboard or by a machine
entering data electronically.
The separation of data from the programs that use the data.
Nearly all modern applications are based on the principle of data independence.
In fact, the whole concept of a database management system (DBMS) supports the
notion of data independence since it represents a system for managing data separately
from the programs that use the data. In contrast, it is possible to write applications
in which the data being processed is actually represented in the program's source
code. This data-dependent approach is very inflexible because it makes it difficult
to modify the data and it also makes the data inaccessible to other programs.
A hot buzzword for a class of database applications that look for
hidden patterns in a group of data. For example, data mining software can help
retail companies find customers with common interests. The term is commonly misused
to describe software that presents data in new ways. True data mining software
doesn't just change the presentation, but actually discovers previously unknown
relationships among the data.
(1) Refers to a class of programs that organize and manipulate
data, usually large amounts of numeric data. Accounting programs are the prototypical
examples of data processing applications. In contrast, word processors, which
manipulate text rather than numbers, are not usually referred to as data processing
Same as Information Technology (IT), refers to all computing functions within
Describes any system based on discontinuous data or events. Computers are digital
machines because at their most basic level they can distinguish between just two
values, 0 and 1, or off and on. There is no simple way to represent all the values
in between, such as 0.25. All data that a computer processes must be encoded digitally,
as a series of zeroes and ones.
opposite of digital is analog. A typical analog device is a clock in which the
hands move continuously around the face. Such a clock is capable of indicating
every possible time of day. In contrast, a digital clock is capable of representing
only a finite number of times (every tenth of a second, for example).
general, humans experience the world analogically. Vision, for example, is an
analog experience because we perceive infinitely smooth gradations of shapes and
colors. Most analog events, however, can be simulated digitally. Photographs in
newspapers, for instance, consist of an array of dots that are either black or
white. From afar, the viewer does not see the dots (the digital form), but only
lines and shading, which appear to be continuous. Although digital representations
are approximations of analog events, they are useful because they are relatively
easy to store and manipulate electronically. The trick is in converting from analog
to digital, and back again.
is the principle behind compact discs (CDs). The music itself exists in an analog
form, as waves in the air, but these sounds are then translated into a digital
form that is encoded onto the disk. When you play a compact disc, the CD player
reads the digital data, translates it back into its original analog form, and
sends it to the amplifier and eventually the speakers.
computers are digital because they consist of discrete units called bits that
are either on or off. But by combining many bits in complex ways, computers simulate
analog events. In one sense, this is what computer science is all about.
To translate into a digital form. For example, optical scanners digitize images
by translating them into bit maps. It is also possible to digitize sound, video,
and any type of movement. In all these cases, digitization is performed by sampling
at discrete intervals. To digitize sound, for example, a device measures a sound
wave's amplitude many times per second. These numeric values can then be recorded
(v) In information technology, to move from summary information to
detailed data by focusing in on something. To drill down through a series of folders,
for example, on a desktop means to go through the hierarchy of folders to find
a specific file or to click through drop-down menus in a GUI. To drill down through
a database is to access information by starting with a general category and moving
through the hierarchy of field to file to record.
Spelled drilldown. The act of focusing in. For example, "He got the information
he needed through a drilldown of the database."
A sequence of special characters that sends a command to a device
or program. Typically, an escape sequence begins with an escape character, but
this is not universally true.
To format data in such a way that it can be used by another application. An application
that can export data can create a file in a format that another application understands,
enabling the two programs to share the same data. The two programs might be different
types of word processors, or one could be a word processor while the other could
be a database management system.
flip side of exporting is importing. Importing refers to the ability of an application
to read and use data produced by a different application. Exporting implies that
the sending application reformats the data for the receiving application, whereas
importing implies that the receiving application does the reformatting.
a set length that never varies. In database systems, a field can have a fixed
or a variable length. A variable-length field is one whose length can be different
in each record, depending on what data is stored in the field.
terms fixed length and variable length can also refer to the entire record. A
fixed-length record is one in which every field has a fixed length. A variable-length
record has at least one variable-length field.
To use data produced by another application. The ability to import data is very
important in software applications because it means that one application can complement
another. Many programs, for example, are designed to be able to import graphics
in a variety of formats.
opposite of importing is exporting, which refers to the ability of one application
to format data for another application.
Integers, floating-point numbers, and character strings constitute the basic data
types that most computers support. There are often different sizes of integers
available; for example, PCs support short integers, which are 2 bytes, and long
integers, which are 4 bytes.
Abbreviation for Indexed Sequential Access Method, a method for managing how a
computer accesses records and files stored on a hard disk. While storing data
sequentially, ISAM provides direct access to specific records through an index.
This combination results in quick data access regardless of whether records are
being accessed sequentially or randomly.
are a number of products that provide basic ISAM access for different operating
systems and program languages.
(1) A button on a keyboard.
In database management systems, a key is a field that you use to sort data. It
can also be called a key field , sort key, index, or key word. For example, if
you sort records by age, then the age field is a key. Most database management
systems allow you to have more than one key so that you can sort records in different
ways. One of the keys is designated the primary key, and must hold a unique value
for each record. A key field that identifies records in a different table is called
a foreign key.
A password or table needed to decipher encoded data.
Often abbreviated LF, a line feed is a code that moves the cursor
on a display screen down one line. In the ASCII character set, a line feed has
a decimal value of 10.
printers, a line feed advances the paper one line. Some printers have a button
labeled LF that executes a line feed when pressed. (Note, however, that the printer
must be in off-line mode to execute a line feed.)
In a form that a computer can accept. Machine-readable data includes
files stored on disk or tape, or data that comes from a device connected to a
computer. Even typewritten pages can be considered machine-readable if you have
an optical character recognition (OCR) system.
Data about data. Meta data describes how and when and by whom a particular
set of data was collected, and how the data is formatted. Meta data is essential
for understanding information stored in data warehouses.
2 to the 50th power (1,125,899,906,842,624) bytes. A petabyte is equal to 1,024
When used to describe
floating-point numbers, precision refers to the number of bits used to hold the
fractional part. The more precision a system uses, the more exactly it can represent
numbers are often classified as single precision or double precision. A double-precision
number uses twice as many bits as a single-precision value, so it can represent
fractional quantities much more exactly.
Like punctuation in human languages, punctuation in programming languages serves
to separate words and phrases. But unlike human punctuation, which is often optional,
computer punctuation is strictly required.
To systematically and permanently remove old and unneeded data. The term purge
is stronger than delete. It is often possible to regain deleted objects by undeleting
them, but purged objects are gone forever.
A quantum bit. The
smallest unit of information in quantum computing. Qubits hold an exponentially
larger amount of information than traditional bits.
Refers to the ability to access data at random. The opposite of
random access is sequential access. To go from point A to point Z in a sequential-access
system, you must pass through all intervening points. In a random-access system,
you can jump directly to point Z. Disks are random access media, whereas tapes
are sequential access media.
terms random access and sequential access are often used to describe data files.
A random-access data file enables you to read or write information anywhere in
the file. In a sequential-access file, you can only read and write information
sequentially, starting from the beginning of the file.
types of files have advantages and disadvantages. If you are always accessing
information in the same order, a sequential-access file is faster. If you tend
to access information randomly, random access is better.
access is sometimes called direct access.
Unprocessed. The term
refers to data that is passed along to an I/O device without being interpreted.
In contrast, cooked refers to data that is processed before being passed to the
term comes from UNIX, which supports cooked and raw modes for data output to a
terminal. In cooked mode, special characters, such as erase and kill are processed
by the device driver before being sent the output device.
Information that has not been organized, formatted, or analyzed.
Short for Resource Description Framework. RDF is a general framework for describing
a Web site's metadata, or the information about the information on the site. It
provides interoperability between applications that exchange machine-understandable
information on the Web. RDF details information such as a site's sitemap, the
dates of when updates were made, keywords that search engines look for and the
Web page's intellectual property rights.
under the guidance of the World Wide Web Consortium, RDF was designed to allow
developers to build search engines that relay on the metadata and to allow Internet
users to share Web site information more readily. RDF relies on XML as an interchange
syntax, creating an ontology system for the exchange of information on the Web.
(v) To copy data to a place where it can be used by a program. The term is commonly
used to describe copying data from a storage medium, such as a disk, to main memory.
The act of reading. For example, a fast disk drive performs 100 reads per second.
Capable of being displayed
(read) and modified (written to). Most objects (disks, files, directories) are
read/write, but operating systems also allow you to protect objects with a read-only
attribute that prevents other users from modifying the object.
Capable of being displayed, but not modified or deleted. All operating systems
allow you to protect objects (disks, files, directories) with a read-only attribute
that prevents other users from modifying the object.
(1) In database management systems, a complete set of information. Records are
composed of fields, each of which contains one item of information. A set of records
constitutes a file. For example, a personnel file might contain records that have
three fields: a name field, an address field, and a phone number field.
relational database management systems, records are called tuples.
Some programming languages allow you to define a special data structure called
a record. Generally, a record is a combination of other data objects. For example,
a record might contain three integers, a floating-point number, and a character
The process of creating and managing duplicate versions of a database. Replication
not only copies a database but also synchronizes a set of replicas so that changes
made to one replica are reflected in all the others. The beauty of replication
is that it enables many users to work with their own local copy of a database
but have the database updated as if they were working on a single, centralized
database. For database applications where users are geographically widely distributed,
replication is often the most efficient method of database access.
Lotus Notes system was one of the first to make replication a central component
of its design, which has been one of the main reasons for its success.
to reading or writing data records in sequential order, that is, one record after
the other. To read record 10, for example, you would first need to read records
1 through 9. This differs from random access, in which you can read and write
records in any order.
programming languages and operating systems distinguish between sequential-access
data files and random-access data files, allowing you to choose between the two
types. Sequential-access files are faster if you always access records in the
same order. Random-access files are faster if you need to read or write records
in a random order.
can also be classified as sequential access or random access. For example, a tape
drive is a sequential-access device because to get to point q on the tape, the
drive needs to pass through points a through p. A disk drive, on the other hand,
is a random-access device because the drive can access any point on the disk without
passing through all intervening points.
A symbol that identifies a number as being either positive or negative. A positive
sign is +; a negative sign is -. These two signs are also used to indicate addition
and subtraction, respectively.
Acronym for Spanning
Tree Protocol. STP, a link management protocol, is part of the IEEE 802.1 standard
for media access control bridges. Using the spanning tree algorithm, STP provides
path redundancy while preventing undesirable loops in a network that are created
by multiple active paths between stations. Loops occur when there are alternate
routes between hosts. To establish path redundancy, STP creates a tree that spans
all of the switches in an extended network, forcing redundant paths into a standby,
or blocked, state. STP allows only one active path at a time between any two network
devices (this prevents the loops) but establishes the redundant links as a backup
if the initial link should fail. If STP costs change, or if one network segment
in the STP becomes unreachable, the spanning tree algorithm reconfigures the spanning
tree topology and reestablishes the link by activating the standby path. Without
spanning tree in place, it is possible that both connections may be simultaneously
live, which could result in an endless loop of traffic on the LAN.
Refers to anything whose length can vary. For example, in databases,
a variable-length field is a field that does not have a fixed length. Instead,
the field length varies depending on what data is stored in it.
fields are useful because they save space. Suppose, for example, that you want
to define a NAME field. The length of each NAME field will vary according to the
data placed in it. For example, John Smith is 10 characters long, but Thomas Horatio
Jefferson is 24 characters long. With fixed-length fields, you would need to define
each field to be long enough to hold the longest name. This would be a waste of
space for records that had short names. With variable-length fields, the NAME
field in each record would be just long enough to hold its data.
opposite of variable length is fixed length.
record that has at least one variable-length field. The length of the entire record,
therefore, varies according to what data is placed in the variable-length field.
Created by Allaire, Web Distributed Data Exchange is an XML -based technology
that facilitates complex-data exchange between Web programming languages (ColdFusion,
example, a Web site based in ColdFusion can share data with a Web site based in
ASP. Data in ColdFusion would be translated into XML, sent to an ASP server, translated
out of XML and into VBScript.
assigns a specific module for each supported language. The module will translate
(or serialize) the native data structures into an abstract form represented as
XML, or deserialize the WDDX XML into a native data structure.
supports Boolean, number, date-time, and string data types, as well as, arrays,
structures, and recordsets.
support for WDDX includes version 3.0 and higher Web browsers (I.E. and Netscape)
for Windows, Unix and Macintosh platforms.
can be used with HTTP, SMTP, POP, and FTP.
To copy data from main memory to a storage device, such as a disk.