APPENDIX A -GLOSSARY OF TERMS

“Hypertext Markup Language (HTML) in computer science is the standard text-formatting language used since 1989 for documents on the interconnected computing network known as the World Wide Web. HTML documents are text files that contain two parts: content that is meant to be rendered on a computer screen and markup or tags, encoded information that directs the text format on the screen and is generally hidden from the user. HTML is a subset of a broader language called Standard Generalized Markup Language (SGML), which is a system for encoding and formatting documents, whether for output to a computer screen or to paper.” [1]

This is not a very sophisticated document. Its only purpose is to display the data “Hello World!” and display a simple graphic. You will note that the instructions to display the image (the <img> tag) are in the form of the URL. That is because the image is not part of the document itself. It merely tells the Web server where to find an image file.

History of HTML

HTML was first developed at the Center for European Particle Research (CERN). At the time, CERN’s need was:

1) To standardize electronic publications formats so research documents could be shared electronically

2) To develop a system to electronically reference, or link, other research documents

ISO Standards, W3C recommendations

HTML was originally a sub-set of SGML, a data format developed to standardize the storage of electronic documents. SGML is recognized under ISO 8879. Its goal is to allow document-based information to be shared and reused across applications and computer platforms in an open, vendor-neutral format.

The World Wide Web Consortium (W3C), founded at MIT in 1994, is the international standards organization for HTML, and a variety of other client and server protocols. W3C has no regulatory authority; however, it is comprised of industry leaders and is directed by Tim Berners-Lee, credited with developing the World Wide Web. One of the strengths of HTML is its broad, global acceptance.

A.2 Other Types of Internet Files

Image File Formats (.jpeg, .gif, .png)

Most of the images on the World Wide Web are compressed. Compression is a way of reordering the information in a digital image so that it takes up less space on a disk (smaller file size). Sometimes the compression can be done without a loss of image quality, but image quality must sometimes be sacrificed.

There are three core standards in the W3C recommendations for image compression: JPEG (abbreviation for Joint Photographic Group), GIF (Graphic Interchange Format)[2] and PNG (Portable Network Graphic). Each of these compression schemes has various “levels” of image compression, trading image quality for file size. Web designers must understand how the compression affects the speed with which a page loads, as well as quality of their images. Files sizes are critical on the Internet - the more data that has to be sent with each page request, the slower the information will get to the user. Web users are notorious for moving on if a Web page takes to long to download.

Each of the compression schemes has advantages and disadvantages. GIF renders areas of flat color well and should be used for diagrams, charts and images where there are areas of sharp contrast and large amounts of flat color. GIF includes a basic animation capabilities and simple image transparency. JPEG compression should be used for full-color images with smooth tonal changes (photographs).

PNG is a newer compression and often a more compact compression technique. PNG can include sophisticated transparencies and renders full-color, smooth tonal images. Unlike the GIF format, it is free of patents and was developed to be a royalty-free replacement to GIF files; however, it is only supported by more recent versions of Web browsers and has yet to gain wide acceptance.

Portable Document Format (.pdf)

Portable Document Format (PDF) files are a proprietary format of the Adobe Acrobat Software. PDF files are written in PostScript, a computer programming language developed to describe images in a device independent manner. It is a popular page description language and it is used by most laser printers (color or black and white). [3]

With the right software, creating a PDF file is essentially the same as printing the file. Instead of a stream of bits and bytes sent to a printer, the bits and bytes are captured to a computer file, and combined with some information (distilled) to be viewed on the screen. The information for a laser printer is still in the file, so, for example, a document can be printed on paper and distributed electronically. The electronic distribution contains the formatting instructions, with fonts and artwork embedded, to make exact copies on printers anywhere.

PDF files can be viewed in a Web browser with special software, or can viewed as stand alone files with special software. The software, called Adobe® Acrobat Reader, is distributed free, and has become the de facto standard for distributing software manuals, and other computer related documents. The viewing software, however, cannot edit, save or create PDF documents.

JavaScript “Client side scripting”

JavaScript was developed by Netscape and the Sun Corporation to extend the capabilities of their Web client software, Netscape Communicator. It was later licensed to Microsoft, which developed its own, slightly different implementation for the Internet Explorer Web browser (see also ActiveX).

JavaScript is called “client side” scripting because it is a language designed to be embedded in an HTML document to control the client (Web browser). If used correctly, it can enhance a Web page with interactive elements, distribute small collections of database-like information, or provide useful utilities to do tasks such as:

When used correctly, JavaScript can reduce the load on a server by eliminating the amount of Server Interaction (see Server Side Scripting below). JavaScript is sent to the viewer’s computer, which then does the computational tasks. However, there is no industry-wide standard for JavaScript, and since each major version of competing Web browser software has a different implementation, developing a universal client-side script is a true challenge.

Perl, Java, CGI – “Server side scripting”

There are many computer languages that can be employed on the Web server to enhance the user experience. Perl, Java, php, C and C++ are some of the more common languages. There is a W3C standard for programs and programming languages that interact with a Web server the Common Gateway Interface (CGI). CGI applications (also called CGI scripts) can extend a Web server, and add the interactive elements that users have come to expect.[4] Because the interactive applications are stored and executed on the Web server, CGI applications are also called “server side scripts.” CGI applications are generally more powerful than client side scripts, however, they increase the load on the Web server.

A CGI application is like a translator or a middleman (sometimes, CGI applications are referred to as “middleware”). A user submits information, or makes a request that is beyond the Web server’s capacity, and a CGI application is invoked. The CGI application determines what resources are needed and translates the user’s information or request from a human friendly format (text, for instance) into a language the resource on the server understands (SQL, for instance). It then waits for a response from the resource, translates the information into a human friendly format, and hands it back the Web server software package, which displays it for the user in a Web browser.

CGI applications can be written to perform a variety of tasks. One common application is to handle on-line forms that e-mail information. It is fairly commonplace to include a feedback form on a Web site that viewers can fill out to send a message to the site administrator. A CGI application on the Web server takes the information that a user fills out and translates it into language that the e-mail server can understand. The e-mail server, at the prompting of the CGI application, e-mails the information to the appropriate recipient.

Other uses for server side applications include connecting users with a database, providing secure areas of a Web site that require a username and password, processing Web server logs (see Section 4.0 Measuring Success) and providing dynamic elements of Web page in response to user information.

Server side applications are generally more complex than client side scripts and require more training and experience to develop, but the results can dramatically improve functionality of the Web site. Traditionally, some basic CGI applications are provided by professional Web hosting companies. Typically, the scripts to write on-line feedback forms are made available as part of a basic hosting package. In general, more complex CGI applications, especially those which provide online access to a database, are written by consultants who specialize in writing server side applications.

Appendix A.3 - Glossary of Technical Terms

[2] Graphic Interchange Format (GIF) is a patent of the Unysis Corporation, who reserves all rights for commercial use.

[4] The term CGI script and CGI application are used interchangeably. A script is often a short application, or an application written in a language that is not compiled. To keep confusion between CGI applications and JavaScript to a minimum, we will use the term 'CGI applicatio'n or simply 'application.'

Appendix A - Glossary of Terms

A.1 What is HTML?