Transaction
In computer programming, a transaction usually means a sequence of information exchange and related work (such as database updating) that is treated as a unit for the purposes of satisfying a request and for ensuring database integrity. For a transaction to be completed and database changes to made permanent, a transaction has to be completed in its entirety. A typical transaction is a catalog merchandise order phoned in by a customer and entered into a computer by a customer representative. The order transaction involves checking an inventory database, confirming that the item is available, placing the order, and confirming that the order has been placed and the expected time of shipment. If we view this as a single transaction, then all of the steps must be completed before the transaction is successful and the database is actually changed to reflect the new order. If something happens before the transaction is successfully completed, any changes to the database must be kept track of so that they can be undone.
A program that manages or oversees the sequence of events that are part of a transaction is sometimes called a transaction monitor. Transactions are supported by Structured Query Language, the standard database user and programming interface. When a transaction completes successfully, database changes are said to be committed; when a transaction does not complete, changes are rolled back. In IBM’s Customer Information Control System product, a transaction is a unit of application data processing that results from a particular type of transaction request. In CICS, an instance of a particular transaction request by a computer operator or user is called a task.
Less frequently and in other computer contexts, a transaction may have a different meaning. For example, in IBM mainframe operating system batch processing, a transaction is a job or a job step.
Transaction Server
The Microsoft Transaction Server (MTS), called "Viper" while it was being developed, is a program that runs on an Internet or other network server with a Windows NT system and manages application and database transaction requests on behalf of a client computer user. The Transaction Server screens the user and client computer from having to formulate requests for unfamiliar databases and, if necessary, forwards the requests to database servers. It also manages security, connection to other servers, and transaction integrity.
The Transaction Server is Microsoft’s bid to make distributed applications and data in a network relatively easy to create. It’s one of a category of programs sometimes known as middleware or multi-tier programming for the enterprise market that IBM has traditionally controlled with its CICS and similar transaction management products.
Microsoft designed the Transaction Server to fit in with its overall object-oriented programming strategy. Using the Transaction Server, you can use a drag-and-drop interface to create a transaction model for a single user, then allow the Transaction Server to manage the model for multiple users, including the creation and management of user and task threads and processes.
MTS runs on Windows NT Server 4.0 or higher.
transactional e-mail
Transactional e-mail is a type of Web-based marketing in which e-mail recipients can buy goods and services directly from an e-mail message, without being redirected to the retailer’s Web site. According to proponents, transactional email leads to significantly higher conversion rates—the ratio of shoppers to buyers, which goes up when the former is converted to the latter—than regular e-mail marketing approaches. A number of different transactional e-mail products are available, from Cybuy, Radical Communication, and EActive, among others.
The transactional e-mail retail experience is easier, and minimizes the tasks involved in online shopping. Within the body of the message, an e-mail recipient can view merchandise, select items, and submit an order. Typically, the e-mail messages contain windows that change to display different products when the recipient clicks listed items. A message assuring the customer of the security of the transaction, and an order form are displayed when the customer clicks the appropriate buttons. When the order form is completed, the customer clicks the "submit" button, and resumes reading their other e-mail messages.
Zagat’s, a well-known distributor of restaurant guides, tried transactional e-mail sales for the 2000 holiday season, allowing customers to buy restaurant guides directly from the body of the e-mail message, rather than just including a link to their Web site. The campaign attained conversion rates five times as high as those of regular e-mail marketing. Besides making shopping simpler for the consumer, transactional e-mail also takes into account the fact that someone who is reading e-mail is doing just that: reading their e-mail. Marketing messages, even for interesting products, may be set aside because they interfere with the task at hand. Even if the consumer wants to buy a product, they may not respond to traditional e-mail marketing messages, because the process involved (going to the retailer’s Web site, going to separate pages to order, and so on) is too cumbersome. Transactional e-mail also makes impulse purchases more likely, because a transaction can be completed before the customer grows weary of the procedures involved.
transceiver
Also see repeater and transponder.
A transceiver is a combination transmitter/receiver in a single package. The term applies to wireless communications devices such as cellular telephones, cordless telephone sets, handheld two-way radios, and mobile two-way radios. Occasionally the term is used in reference to transmitter/ receiver devices in cable or optical fiber systems. In a radio transceiver, the receiver is silenced while transmitting. An electronic switch allows the transmitter and receiver to be connected to the same antenna, and prevents the transmitter output from damaging the receiver. With a transceiver of this kind, it is impossible to receive signals while transmitting. This mode is called half duplex. Transmission and reception often, but not always, are done on the same frequency.
Some transceivers are designed to allow reception of signals during transmission periods. This mode is known as full duplex, and requires that the transmitter and receiver operate on substantially different frequencies so the transmitted signal does not interfere with reception. Cellular and cordless telephone sets use this mode. Satellite communications networks often employ full-duplex transceivers at the surface-based subscriber points. The transmitted signal (transceiver-to-satellite) is called the uplink, and the received signal (satellite-to-transceiver) is called the downlink.
transcendental number
A transcendental number is a real number that is not the solution of any single-variable polynomial equation whose coefficients are all integers. All transcendental numbers are irrational numbers. But the converse is not true; there are some irrational numbers that are not transcendental.
Examples of transcendental numbers include pi, the ratio of a circle’s circumference to its diameter in a plane, and e, the base of the natural logarithm. The case of pi has historical significance. The fact that pi is transcendental means that it is impossible to draw to perfection, using a compass and straightedge and following the ancient Greek rules for geometric constructions, a square with the same area as a given circle. This ancient puzzle, known as squaring the circle, was, for centuries, one of the most baffling challenges in geometry. Schemes have been devised that provide amazingly close approximations to squaring the circle. But in theoretical mathematics (unlike physics and engineering), approximations are never good enough; a solution, scheme, or method is either valid, or else it is not.
It can be difficult, and perhaps impossible, to determine whether or not a certain irrational number is transcendental. Some numbers defy classification (algebraic, irrational, or transcendental) to this day. Two examples are the product of pi and e (call this quantity Ppie) and the sum of pi and e (call this Spie). It has been proved that pi and e are both transcendental. It has also been shown that at least one of the two quantities Ppie and Spie are transcendental. But as of this writing, no one has rigorously proven that Ppie is transcendental, and no one has rigorously proved that Spie is transcendental.
transcoding
Transcoding is a technology used to adapt computer application displays and Web content so that they can be viewed on any of the increasingly diverse devices on the market. Transcoding servers and services reformat material that would otherwise have to be developed separately for display on different platforms. Working like an interpreter, the technology translates content to suitable formats for various platforms, regardless of protocol, application, screen size, and language used. A variant of transcoding has been used for some time in Web applications such as AltaVista’s Babel Fish language translation program.
Although wireless connectivity is steadily increasing, the question of how to enable content display has been problematic. Handheld wireless devices—such as the smartphone and the personal digital assistant (PDA)—tend to have limitations in terms of power, memory, resolution, and screen size; this means that they have problems displaying Web content suitable for a full-sized computer. Typically, the mobile user wants to be able to access the crucial data (such as a stock quote, for example) without any extra detail or graphic display. Without transcoding, content must be written specifically (and separately) to meet the requirements and constraints of each device, and the process must be repeated every time the content is updated. Manual reauthoring of content can cause problems for a mobile workforce that depends on getting reliable information. Each time content is rewritten, possibilities for errors exist, and updates may not always be available simultaneously for all devices.
There are two main options for those who want to automate the reformatting of content: Using a transcoding server product, such as Aether’s Scout Web, AvantGo’s Enterprise Server, or IBM’s WebSphere Transcoding Publisher, or using a transcoding service, such as Everypath. Although the server products offer the most control over the final content, they also require in-house expertise, as developers must work directly with the original HTML and eXtensible Markup Language (XML) content. Transcoding services are application service providers (ASPs) that take responsibility for the entire process and deliver the reformatted content from legacy material.
There are a number of different ways that transcoding can take place. In one example, the original material (an HTML or XML document, for example) is analyzed by a program that then creates a separate version (rather than changing the source) that contains annotations. The annotations include information that will instruct the reformatting process, such as importance ratings of document elements, for example, so that when space is limited, non-essential elements will not be displayed. When a request for the document is sent to the hosting server, the server submits the annotated version to an authoring application. The material is reformatted there, and sent on to a transcoding proxy server. The proxy server accesses information about device preferences, and may adapt the material further before delivering it to the end user. The device user may also have specific display preferences, either previously set in the device, or chosen at the time that they request the document, so that the document is reformatted dynamically.
transconductance
Transconductance is an expression of the performance of a bipolar transistor or field-effect transistor (FET). In general, the larger the transconductance figure for a device, the greater the gain (amplification) it is capable of delivering, when all other factors are held constant.
Formally, for a bipolar device, transconductance is defined as the ratio of the change in collector current to the change in base voltage over a defined, arbitrarily small interval on the collector-current-versus-base-voltage curve. For an FET, transconductance is the ratio of the change in drain current to the change in gate voltage over a defined, arbitrarily small interval on the drain-current-versus-gate-voltage curve. The symbol for transconductance is gm. The unit is the siemens, the same unit that is used for direct-current (DC) conductance.
If dl represents a change in collector or drain current caused by a small change in base or gate voltage dE, then the transconductance is approximately:
As the size of the interval approaches zero—that is, the change in base or gate voltage becomes smaller and smaller—the value of dl / dE approaches the slope of a line tangent to the curve at a specific point. The slope of this line represents the theoretical transconductance of a bipolar transistor for a given base voltage and collector current, or the theoretical transconductance of an FET for a given gate voltage and drain current.
transducer
A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antennas. Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers.
Efficiency is an important consideration in any transducer. Transducer efficiency is defined as the ratio of the power output in the desired form to the total power input. Mathematically, if P represents the total power input and Q represents the power output in the desired form, then the efficiency E as a ratio between 0 and 1 is given by:
If E represents the efficiency as a percentage, then:
No transducer is 100-percent efficient; some power is always lost in the conversion process. Usually this loss is manifested in the form of heat. Some antennas approach 100-percent efficiency. A well-designed antenna supplied with 100 watts of radio frequency (RF) power radiates 80 or 90 watts in the form of an electromagnetic field. A few watts are dissipated as heat in the antenna conductors, the feed line conductors and dielectric, and in objects near the antenna. Among the worst transducers, in terms of efficiency, are incandescent lamps. A 100-watt bulb radiates only a few watts in the form of visible light. Most of the power is dissipated as heat; a small amount is radiated in the UV (ultraviolet) spectrum.
transient cookie
On the Web, a transient cookie, sometimes called a session cookie, is a small file that contains information about a user that disappears when the user’s browser is closed. Unlike a persistent cookie, a transient cookie is not stored on your hard drive but is only stored in temporary memory that is erased when the browser is closed.
A transient cookie is created by simply not setting a date in the Set-Cookie option when an application creates the cookie. (For a persistent cookie, an expiration date is set and the cookie is stored on the user’s hard drive until the expiration date or until the user deletes it.)
Transient cookies are often used to enable a site to be able to track the pages that a user has visited during a visit so that information can be customized for the user in some way. Some sites use Secure Sockets Layer (SSL) to encrypt the information contained in a cookie.
transistor
The transistor, invented by three scientists at the Bell Laboratories in 1947, rapidly replaced the vacuum tube as an electronic signal regulator. A transistor regulates current or voltage flow and acts as a switch or gate for electronic signals. A transistor consists of three layers of a semiconductor material, each capable of carrying a current. A semiconductor is a material such as germanium and silicon that conducts electricity in a "semi-enthusiastic" way. It’s somewhere between a real conductor such as copper and an insulator (like the plastic wrapped around wires).
The semiconductor material is given special properties by a chemical process called doping. The doping results in a material that either adds extra electrons to the material (which is then called N-type for the extra negative charge carriers) or creates "holes" in the material’s crystal structure (which is then called P-type because it results in more positive charge carriers). The transistor’s three-layer structure contains an N-type semiconductor layer sandwiched between P-type layers (a PNP configuration) or a P-type layer between N-type layers (an NPN configuration).
As the current or voltage is changed in one of the outer semiconductor layers, it affects a larger current or voltage in the inner layer resulting in the opening or closing of an electronic gate. Today’s computers use circuitry made with complementary metal oxide semiconductor (CMOS) technology. CMOS uses two complementary transistors per gate (one with N-type material; the other with P-type material). When one transistor is maintaining a logic state, it requires almost no power.
Transistors are the basic elements in integrated circuits (ICs), which consist of very large numbers of transistors interconnected with circuitry and baked into a single silicon microchip or "chip."
transit
Transit is the connection to and use of a telecommunication path provided by a vendor. Transit may be billed separately or, where peering is also provided, may be billed as part of the peering charge.
Transmeta
Transmeta is a Silicon Valley start-up company known for its recruitment of high profile talent and its Crusoe chip, designed for mobile Internet computing. David Ditzel (Sun UltraSparc) founded Transmeta in 1995 and recruited Linus
Torvalds, the creator of Linux, to be a member of Transmeta’s software team. (Paul Allen, co-founder of Microsoft is a major investor.) For four and a half years, the company operated in a shroud of secrecy, causing a lot of speculation about what Transmeta actually did. In November of 2000, Transmeta went public and revealed it had developed a low-power microprocessing chip called Crusoe (named after Daniel Defoe’s shipwrecked character, Robinson Crusoe). Crusoe is the first of what Transmeta hopes will be a family of smart microprocessors for mobile Internet devices.
transparent GIF
A transparent GIF (Graphics Interchange Format) is an image file that has one color assigned to be "transparent" so that the assigned color will be replaced by the browser’s background color, whatever it may be. Pretend, for example, that you have created a rectangular GIF image of a large red star on a white background. If you are only interested in having the red star appear on your Web page, and don’t want to see the white background, you can transparentize the white background color so that it changes to whatever the Web page’s background color is (yellow, for example). Then, when you view the Web page, you will only see a red star on a yellow background.
A single color transparent GIF can also be used as a place holder in a table cell on a Web page. Another name for this use of a transparent GIF is "spacer GIF."
transponder
A transponder is a wireless communications, monitoring, or control device that picks up and responds to an incoming signal. The term is a contraction of the words transmitter and responder. Transponders can be either passive or active.
A passive transponder allows a computer or robot to identify an object. Magnetic labels, such as those on credit cards and store items, are common examples. A passive transponder must be used with an active sensor that decodes and transcribes the data the transponder contains. The transponder unit can be physically tiny, and its information can be sensed up to several feet away. Simple active transponders are employed in location, identification, and navigation systems. An example is an RFID (radio-frequency identification) device that transmits a coded signal when it receives a request from a monitoring or control point. The transponder output signal is tracked, so the position of the transponder can be constantly monitored. The input (receiver) and output (transmitter) frequency are preassigned. Transponders of this type can operate over distances of thousands of miles.
Sophisticated active transponders are used in communications satellites and on board space vehicles. They receive incoming signals over a range, or band, of frequencies, and retransmit the signals on a different band at the same time. The device is similar to a repeater of the sort used in land-based cellular telephone networks. The incoming signal, usually originating from a point on the earth’s surface, is called the uplink. The outgoing signal, usually sent to a point or region on the surface, is the downlink. These transponders sometimes operate on an interplanetary scale.
Transport layer
In the Open Systems Interconnection (OSI) communications model, the Transport layer ensures the reliable arrival of messages and provides error checking mechanisms and data flow controls. The Transport layer provides services for both "connection-mode" transmissions and for "connectionless-mode” transmissions. For connection-mode transmissions, a transmission may be sent or arrive in the form of packets that need to be reconstructed into a complete message at the other end.
The Transmission Control Protocol portion of TCP/IP is a program that can be mapped to the Transport layer.
Transport Layer Security
Transport Layer Security (TLS) is a protocol that ensures privacy between communicating applications and their users on the Internet. When a server and client communicate, TLS ensures that no third party may eavesdrop or tamper with any message. TLS is the successor to the Secure Sockets Layer (SSL).
TLS is composed of two layers: the TLS Record Protocol and the TLS Handshake Protocol. The TLS Record Protocol provides connection security with some encryption method such as the Data Encryption Standard (DES). The TLS Record Protocol can also be used without encryption. The TLS Handshake Protocol allows the server and client to authenticate each other and to negotiate an encryption algorithm and cryptographic keys before data is exchanged.
The TLS protocol is based on Netscape’s SSL 3.0 protocol; however, TLS and SSL are not interoperable. The TLS protocol does contain a mechanism that allows TLS implementation to back down to SSL 3.0. The most recent browser versions support TLS. The TLS Working Group, established in 1996, continues to work on the TLS protocol and related applications.
Trap
1) In a Web site, a trap is a page that does not allow the reader to back up a previous page (the Back button on the toolbar is inoperable). A few Web site creators apparently use this technique to hold the reader and force them to read the page or to encourage them to visit other pages on their site. To exit a trap, the reader must either close the browser and open it again or enter a URL on the address line. Traps are highly unpopular among Web users.
2) In assembler language programming, a trap is a place in a program for handling unexpected or unallowable conditions—for example, by sending an error message to a log or to a program user. If a return code from another program were being checked by a calling program, a return code value that was unexpected and unplanned for could cause a branch to a trap that recorded the situation and took other appropriate action.
