Analog
Almost everything 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.

Digital 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.

Early attempts at building computers used analog techniques, but accuracy and reliability were not good enough. Today, almost all computers are digital.

Attribute
(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 attribute.

(2) In database management systems, the term attribute is sometimes used as a synonym for field.

(3) 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.

BER
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.

BERT
Short for bit error rate test, or tester, a procedure or device that measures the bit error rate of a transmission.

BLOB
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.

BPDU
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.

Browse
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.

Burst
(n) A set of bits, bytes or characters grouped together for transmission.

(v) An intermittent asynchronous transmission of a specific amount of data. Contrast with streaming.

Comma-Delimited
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.

Control Character
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.

Convert
To change data from one format to another.

Corrupted
Refers to data that has been damaged in some way.

Data
(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.

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.

Strictly 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.

(2) 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).

(3) 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.

Data Dictionary
In 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.

Data 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.

Data Entry
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.

Data Independence
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.

Data Mining
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.

Data Processing
(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 applications.

(2) Same as Information Technology (IT), refers to all computing functions within an enterprise.

Digital
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.

The 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).

In 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.

This 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.

Internally, 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.

Digitize
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 digitally.

Drill Down
(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.

(n) Spelled drilldown. The act of focusing in. For example, "He got the information he needed through a drilldown of the database."

Escape Sequence
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.

Export
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.

The 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.

Fixed Length
Having 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.

The 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.

Import
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.

The opposite of importing is exporting, which refers to the ability of one application to format data for another application.

Integer
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.

ISAM
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.

There are a number of products that provide basic ISAM access for different operating systems and program languages.

Key
(1) A button on a keyboard.

(2) 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.

(3) A password or table needed to decipher encoded data.

Line Feed
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.

On 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.)

Machine Readable
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.

Meta Data
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.

Petabyte
2 to the 50th power (1,125,899,906,842,624) bytes. A petabyte is equal to 1,024 terabytes.

Precision
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 fractional quantities.

Floating-point 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.

Punctuation
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.

Purge
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.

Qubit
A quantum bit. The smallest unit of information in quantum computing. Qubits hold an exponentially larger amount of information than traditional bits.

Random Access
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.

The 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.

Both 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.

Random access is sometimes called direct access.

Raw
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 I/O device.

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.

Raw Data
Information that has not been organized, formatted, or analyzed.

RDF
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.

Developed 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.

Read
(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.

(n) The act of reading. For example, a fast disk drive performs 100 reads per second.

Read/Write
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.

Read-Only
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.

Record
(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.

In relational database management systems, records are called tuples.

(2) 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 string.

Replication
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.

The 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.

Sequential Access
Refers 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.

Some 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.

Devices 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.

Sign
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.

STP
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.

Variable Length
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.

Variable-length 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.

The opposite of variable length is fixed length.

Variable-Length Record
A 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.

WDDX
Created by Allaire, Web Distributed Data Exchange is an XML -based technology that facilitates complex-data exchange between Web programming languages (ColdFusion, Perl, ASP, Java, JavaScript, PHP, etc.).

For 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.

WDDX 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.

WDDX supports Boolean, number, date-time, and string data types, as well as, arrays, structures, and recordsets.

Browser support for WDDX includes version 3.0 and higher Web browsers (I.E. and Netscape) for Windows, Unix and Macintosh platforms.

WDDX can be used with HTTP, SMTP, POP, and FTP.

Write
To copy data from main memory to a storage device, such as a disk.