DITA 06 - CSS

The concept behind the Document Object Model (DOM) is that all well formed XML and HTML documents are hierachical and reflected in the program-like nested structure of clear XML/HTML. This tree structure of nodes consisting of elements and text where elements have a unique identifier (id) and text cannot have any further nodes within.

A further development toward clear information management in web HTML is the Cascading Style Sheet (CSS) which allows the web designer/coder to separate out text and image file content from instructions on how to layout the information when the web page or website is presented. An example of how the same content can be represented by differing CSS instructions can be seen at the css Zen Garden site. CSS standards are set by W3C.

A general form of CSS code is:

selector, selector, ... {property1:value1; property2:value2; ... propertyN:valueN;}

This example defines selectors Heading1 and 2 and gives them the same property/values
for colour and font

Heading1, Heading2
{
color: red;
font-family: tahoma
}

Where selectors are used to identify those areas of the document in which to follow the style declarations inside brackets {declaration, declaration}. Each declaration provides properties and values, like colour and type face to apply in the selected part of the document. An example is shown here.

CSS can also define positioning of text and graphics elements of the web page. Positioning can be static - in the document flow, relative - changeable with reference to it's stated position or absolute - a fixed position anywhere in the document.

Benefits of CSS include:

• Single down load of the CSS instructions which can cover an enter website layout
• Reduced data loading for the website and less memory usage
  
• The ability to decide at the point of delivery how to use the layout in the CSS once platform is known - different layout for a PC screen and a handheld device
  
• The ability to let the web user select a layout e.g. for large text if partially sighted - link to RNIB Web Accessibility pages
  

Disadvantage of CSS

• Differences between browser software (e.g. versions of MSInternet Explorer, Firefox, Safari etc) give different representations for the same CSS instructions.

DITA 05 - XML

eXtensible markup language (XML) is a flexible and easy to use form of Mark Up meta language that can be used across the WWW and contains elements within open and close tags, and attributes which give properties or values to tags. It supports clear interfacing of information between many different types of programs and in many different user domains.

Despite the user flexibility in XML it has rules and XML code must be well formed and valid. One example of the structuring inherent in XML is shown in the Document Type Definition (DTD).

This example Document Type Definition (DTD) shows how a host system transferring address date to a delivery service handheld could constrain data to allow unambiguous transfer:

An example domain for the use of XML approach is Geographic information interchange which can be facilitated by a version of XML called GML (Geography Markup Language) and also GPX which has been created for exchange of GPS (global positioning satellite) information such as heading, track etc.).

The following extract from the Bos, B. (2001), “XML in 10 points” website describes the key attributes of XML and it’s user definable flexibility:

“Like HTML, XML makes use of tags (words bracketed by '<' and '>') and attributes (of the form name="value"). While HTML specifies what each tag and attribute means, and often how the text between them will look in a browser, XML uses the tags only to delimit pieces of data, and leaves the interpretation of the data completely to the application that reads it. In other words, if you see "

A key benefit of XML is that it separates document content from semantic or presentational information. This allows the transmission of information to different types of platform (PC, handheld, text reader) with decisions about presentation left until the delivery environment is known aiding interoperability across different types of web program.