ASF from Microsoft,
allows data of different media types (audio, video, image) to
be placed into a single file that is stored on a server. When
a user requests to see a presentation, the server takes the file,
splits it into packets, and puts a "presentation timestamp"
into each packet. The client uses these timestamps to synchronise
the different packets when it replays the file.
An animated
GIF is a GIF 89afile containing multiple images. These images
act as successive frames of animation when the GIF is viewed in
a web browser.
Browser
There are
many different types of Browsers, however in the main people tend
to use Internet Explorer & Netscape Communicator.
A popular
type of HTML rendering device used by personal computers connected
to the Internet. Browser programs include Acorn-Browse, AIR Mosaic,
ANT Fresco, Avanti, Amiga-A-Web, Amiga Voyager, Arc Web, Cyberdog,
Echo, France Explorer, Hot Java, IBM-Web Explorer, I-Browse (Amiga),
InterGO, Lotus-Notes, Lynx, Mac Web, MSHTML, Internet Explorer,
Pocket Internet Explorer, Mac Web (Macintosh), Mercer OS, NCSA
Mosaic, Net Positive (Be OS), Netscape Communicator, Netscape
Navigator, Near Site, Opera, Palmscape (Palm Pilot), Quarterdeck
Mosaic, Spry Mosaic, Spyglass Mosaic, Voyager (Acorn), Web Compass,
Webster XL (Acorn), Web Whacker.
An HTML syntax
that gives authors precise control over the formatting of text
in Web pages. Formatting information is stored in a Web site in
style sheets, and can be applied to whole pages or parts of pages.
A client-side
image map requires image map information to be stored within the
HTML document. A client-side image map shows the actual URL in
the status bar message at the bottom of the browser window.
A server-side
(NCSA) image map requires the image map information to be saved
within a separate file stored on a server and accessed by a CGI
script. This type of image map is far more complicated to set
up, and is not supported by all servers. Server-side image map
behaviour varies from system to system, even among different systems
using the same server. A server-side image map shows the co-ordinates
at the bottom of the screen.
CSS
Acronym
for Cascading Style Sheet. Styles can be defined in a separate
style sheet document, at the top of the current document, or
within individual HTML tags. Each level of definition can override
attributes set by the next higher style definition.
A standard
method of extending Web server functionality by executing programs
or scripts on a Web server in response to Web browser requests.
A common use of CGI is in form processing, where the browser sends
the form data to a CGI script on the server, and the script integrates
the data with a database and sends back a results page as HTML.
Methods for
combining scripts, style sheets, HTML extensions, downloadable
content and fonts, to create interactive Internet documents. DHTML
offers the promise of greater control over the real-time appearance,
content, layout, and behaviour of documents. DHTML, while a significant
and complex enhancement, is subject to proprietary implementations
and competing standards.
The ability
to change style or positioning properties with a scripting language
is what is commonly called dynamic HTML, or DHTML. There are four
DHTML-related features: Layers, Styles, Timelines, and Behaviours.
DHTML features work only in 4.0 or later browsers. (Internet Explorer
3.0 partially supports style sheets.)
Like halftone
pictures in newspapers, dithering uses patterns of colour pixels
to replace pure colours. Dithering is used to simulate colours,
especially for computers that can represent a limited number of
colours. For example, combine patterns of red and yellow to simulate
orange.
Frames divide
a Web browser's window into separate regions, each of which can
display a separate, scrollable page. A group of frames is called
a frames page. A frames page is a special Web page that defines
the size and location of each frame it contains.
In the simplest
frames page there are two frames: one frame displays a page listing
a set of hyperlinks, and the other frame displays the pages to
which the hyperlinks point. Each time a user clicks a hyperlink
in the first frame, the page pointed to by that hyperlink is displayed
in the second frame. The frames page itself does not actually
contain any content or pages; it contains only hyperlinks to existing
pages that are displayed in the frames.
GIF (Graphics
Interchange Format) is a bitmap format developed by CompuServe
to easily transfer graphic files online. GIF is an 8-bit (256-colour)
format that uses LZW compression to make bitmap files smaller-about
half of their original size. The GIF format uses the 256 most
representative colours for the image so that the final images
have small file sizes, but good image quality.
A GIF is usually
ideal for cartoon-like graphics, logos, graphics with transparent
areas, or animation.
Compression
Loss-less
compression means that no image quality is lost when an image
is compressed. A GIF compresses by scanning horizontally across
a row of pixels, finding solid areas of colour, and then abbreviating
identical areas of pixels in the file. Therefore, images with
repetitive areas of solid colour compress best when saved as GIFs.
Note Dithering
or anti-aliasing GIF images produces larger files.
Transparency
is defined in GIF files by designating one or more colours to
be transparent. The designated colour is transparent when the
GIF is viewed in a browser.
A pointer
from text or from an image map to a page or other type of file
on the World Wide Web. On Web pages, hyperlinks are the primary
way to navigate between pages and among Web sites.
An image
map is a graphic with URLs assigned to hotspot regions of the
graphic from within an HTML file. Clicking a hotspot in a web
browser opens the web page to which the URL links. A well-designed
image map can add significantly to the visual impact of a web
site.
A general-purpose
programming language created by Sun Microsystems. Java can be
used to create Java applets. A Java program is downloaded from
the Web server and interpreted by a program running on the computer
running the Web browser.
A short program
written in Java that is attached to a Web page and executed by
the computer on which the Web browser is installed.
A cross-platform,
World Wide Web scripting language developed by Netscape Communications.
JavaScript code is inserted directly into an HTML page.
JPEG is a
loss'y format, which means that some image data is discarded when
it is compressed, reducing the quality of the final file. However,
image data can often be discarded with little or no noticeable
difference in quality.
The JPEG format
is best for scanned photographs, images using textures, images
with gradient colour transitions, or any images that require more
than 256 colours.
The Portable
Network Graphic, or PNG, is the most versatile of the web graphic
formats. However, not all web browsers can take full advantage
of PNG characteristics. A PNG supports up to 32-bit colour, can
contain transparency or an alpha channel, and can be progressive.
PNG
Compression
PNG compression
is loss-less, even in high colour depths. It compresses across
rows and columns of pixels, yielding better compression than GIF,
which only scans rows. A PNG can compress more than a GIF or JPEG
of the same colour depth and quality.
The PNG format is best suited for creating complex live transparency,
high-colour graphics, or better-compressed low-colour graphics.
We think PNG will be the future format for graphic files on the
web, but not until most browsers are able to read PNG format.
RTSP is different
from the other two, since it is a protocol which contains protocol
messages that allow you to control an on-demand streaming media
server. It basically allows the same level of control as a video
recorder, i.e., you can say "play," "stop,"
"fast forward," etc.
A new generation
of search engines and Net tools has started to arrive. These attempt
to bring a certain amount of intelligence to the process of Internet
searching. Although few boast databases the size of the likes
of Alta Vista, or the speed of some of their contemporaries, used
correctly some of these new tools can become valuable companions.
Targeted search engines that only look at a section of the Web,
and engines which allow you to configure their results into a
more readable format are popping up all over the place.
Targeted
search engines
There are
already plenty of localised search engines appearing. Most of
the big names have UK versions, although these often only include
local guides and advertising white the main engine stays unchanged.
These types
of engines are now appearing the world over. To take one example,
Australian and New Zealand users can peruse the fast and powerful
Answers service at www.anzwers.com.au, which uses lnktomi technology
to deliver localised results.
Vertical market
search engines are also starting to appear. Exes at www.exes.com
is a travel-oriented engine. A new service with a relatively small
database, the software searches relevant travel sites such as
traffic reports, live CAMs, immigration news, and visa information.
Expect to see more of these types of engines appearing in the
coming months.
Northern Light
concentrates on presenting search results in an easily digestible
format. You can set up Custom Search Folders which organise your
search results by subject, source or type -hugely useful for searches
where thousands of results are delivered.
You can also
search Northern Light's Special Collection, which claims to include
content you will not be able to find elsewhere. This search engine
seems to be asking all the right questions, and certainly makes
searching a less frustrating experience.
See
the best of the top search engines
Structured
Generalised Markup Language. Defines the logical organisation
of a document and syntax of layout elements.
An object
that describes document formatting, such as colour, font and size.
Styles can be defined in a separate style sheet document, at the
top of the current document, or within individual HTML tags.
To make authoring
of TV-like multimedia presentations on the Web easier, W3C has
designed the Synchronised Multimedia Integration Language (SMIL,
pronounced "smile"). SMIL is an easy-to-learn HTML-like
language allowing to use a text editor to write multimedia presentations
with streaming audio and video.
There is significant
interest to integrate and synchronise Web content with audio and
video information transmitted over the TV signal. To study this
in more detail, W3C has organised a workshop
on "Television and the Web".
Tables are
made up of rows and columns of cells that can contain anything
you might put on a page, such as text, images, forms, ActiveX
controls, or components. You can use tables to arrange data systematically
or to organise the layout of a page. A table allows you to display
text in side-by-side paragraphs or arrange text next to graphics.
Use a table to simulate columns of text, or use a fixed-pixel-width
column to provide a margin for text on a page.
GIF images
are also capable of defining one of its colours as transparent,
so that when the GIF is placed over another image, either online
or in a bitmap editing application, the bottom image is seen through
areas defined as transparent. GIF images may contain completely
transparent or completely opaque areas; partial transparency is
not supported.
A multi-user,
multitasking operating system that exists in various forms and
implementations, typically used on proprietary computer workstations.
Many Web servers run on UNIX systems.
Microsoft
Visual Basic Scripting Edition, a subset of the Microsoft Visual
Basic programming system. Microsoft Internet Explorer version
3.0 and higher, along with other Web browsers, can read VBScript
programs embedded in HTML pages. VBScript programs can be executed
either on the Web server, or on the computer on which the Web
browser is installed. In the FrontPage Editor, you can insert
and edit VBScript code.
A short video
sequence that can be embedded into a Web page. Video clips can
be inserted into FrontPage using ActiveX Controls, VBScript, Java
applets, or plug-ins.
Extensible
Markup Language. A proposed standard, based on SGML, for flexible
display of data-based documents.
Comparison
of web formats
| |
GIF
|
JPEG |
PNG |
Colour
depth
|
8-bit
maximum |
Up
to 24-bit |
Up
to 32-bit |
Compression
|
Loss-less;
compresses solid areas of colour |
Lossy;
compresses subtle colour transitions |
Loss-less |
Transparency
support
|
Yes |
No |
Yes |
Advantages
|
Loss-less
compression Transparency |
Ability
to control quality loss in compression Excellent compression
of photographic images |
Loss-less
compression Alpha transparency High colour support |
Disadvantages
|
Maximum
of 256 colours Does not compress gradient colours well |
No
transparency Loss of quality when compressed |
Not
completely supported by common browsers without using plug-ins |
Typical
Uses
|
Cartoon
images Logos Animated banners |
Scanned
photographs Images with complex textures Images with complex
gradient colours |
Images
with high numbers of colours Complex, live transparency |
Common
HTML tags
Most HTML documents
contain the following tags:
<HTML></HTML>
Marks the beginning
and ending of the HTML document.
<TITLE></TITLE>
Sets the name
of the document that appears on the top of the browser window.
<HEAD></HEAD>
Information
in this section describes various characteristics of the document
such as the document title, background colour, text colour, and
font usage. JavaScript code is placed within this section of the
document.
<META></META>
Stores extra
information about the HTML document such as what application created
it, keywords for search engines, and other information used by various
applications. Many HTML editors or utilities add meta information
to an HTML document.
<SCRIPT></SCRIPT>
Marks the beginning
of code for a scripting language, such as JavaScript.
<BODY></BODY>
Text or links
in this section go into the main body of the document.
<IMG>
Displays an
image on the web page. For example:
<IMG SRC="Picture.gif">
This tag displays
the image Picture.gif on the page.
<A></A>
Creates a link
from text or an image to another HTML document. For example:
<A HREF="http://www.ark.uk.com">Link</A>
In this case,
clicking the word "Link" jumps to www.ark.uk.com.
To place an
image and also make that image a link, use two tags:
<A HREF="http://www.ark.uk.com">
<IMG SRC="Explosion.jpg"></A>
The image Explosion.jpg
is displayed on the web page and clicking on it takes you to www.getfireworks.com.
Note that the link to the image is placed within the link tags,
between <A> and </A>.
<MAP></MAP>
Information
within this tag describes the shape of a hotspot using co-ordinates
and contains the URL destination of the hotspot.
|
