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(computer science)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


On drawings, abbr. for switch.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

Semantic Web

A distributed collection of "linked data" on the Web. Just as Web pages are linked together via hypertext, the goal of the Semantic Web is to ultimately link all the available public data.

Sometimes called "Web 3.0," the purpose of the Semantic Web is to make searches more effective. As information has grown exponentially on the Web, search engines routinely return countless result links when, very often, only one or two items of data are required to answer a query. Wading through the articles has turned people into research analysts whether they were ready for the task or not.

More Summaries Than Before
One cannot help but notice that results from search engines increasingly deliver a concise summary of facts about the subject of the query in addition to the Web page links. These summaries are derived from semantic-oriented knowledge bases.

URIs and RDF Models
The Semantic Web uses URIs to identify the data, the RDF data model to structure the relationships and numerous ontological vocabularies that provide the definitions. See ontology, URI, RDF, semantic browser and semantic search.

Who's Developing the Semantic Web?
Knowledge bases structured with semantic meaning are continuously being developed by government and private industry as well as community driven. At some point, Google's knowledge base may wind up being the world's largest (see Google Knowledge Vault). See virtual assistant, Wikidata, Freebase and DBpedia.


Software on the "honor system." The concept is that users try a product, and if they like it, they voluntarily pay a set registration fee or make a donation to the program's creator. There are tens of thousands of shareware programs; some fantastic, some awful.

Typically written part time by individuals, shareware had its heyday in the 1980s and early 1990s. Although some applications were successful, the bulk were not, and most shareware evolved into trial versions that work for a limited time or lite versions that have limited functionality (see trialware and lite version).

The Shareware Heydays
Prior to the Web, "shareware vendors" copied hundreds of shareware programs onto floppy disks and CD-ROMs and sold them by mail order or at computer flea markets. They collected a small fee for the distribution service, although novices often thought it was the software registration fee. In the late 1990s, advertiser-supported shareware websites sprang up to provide distribution. See crippleware, freeware, public domain software, ad-supported software and wares.

shortwave radio

Radio transmission in the 1.7-30 MHz frequency range worldwide. Like AM radio, shortwave signals reflect back from the ionosphere and follow the curvature of the earth. As a result, shortwave (SW) signals can span hundreds and even thousands of miles.

The shortwave term was coined in the early 1900s when radio emerged, and the spectrum was divided into short, medium and long wavelengths. Ham radio operators continue to use the shortwave bands (see amateur radio). See AM radio and FM radio.


Instructions for the computer. A series of instructions that performs a particular task is called a "program." The two major software categories are "system software" and "application software."

System Software Runs the Computer
System software is made up of the operating system and other control programs for managing the hardware and running the applications.

Application Software Runs the Business
Application software is any program that processes data for the user (inventory, payroll, spreadsheet, word processor). Even games and DVD playback software are applications. The terms "software," "program" and "application" are synonymous and commonly interchanged in the same discussion. See system software, application software, information system, data processing and wares.

Software Is Not Data
A common misconception is that software is data. It is not. Software tells the hardware how to process the data.

     Software is "run."Data are "processed."


A speaker that reproduces the lower end of the audio spectrum. A subwoofer system typically includes a crossover circuit that filters frequencies around 100Hz and under to the driver. In a home theater, the placement of front, center and surround speakers is critical to the listener, but subwoofers are non-directional and can be located in a convenient spot, although corners are not recommended.

Passive and Active Subwoofers
Passive subwoofers contain only the speaker (the driver) and crossover. Active subwoofers are self powered and include their own amplifier. See woofer.
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