In Module X01c, the vision of the Semantic Web was introduced. In order to bring this vision to reality, one step Web designers must take is to separate content and structure from presentation. In this module, we'll look at details of some of structure, content, and presentation.

There are two kinds of structure that concern Web design:

1. Logic structure
2. Syntactic structure

Logic structure is the underlying organization of the information. Logic structure is often expressed in outlines.

A good designer will create a logical structure for a document first, then consider the syntactic options for expressing that logic structure.

Syntactic structures are the units of code+information in a Web page. For example, we can code structures such as paragraphs, lists, and tables for our pages.

Since the purpose of a Web page is to display information clearly and attractively, the logic structure is the first type of structure to consider. Designers need to be creative in using syntactic structures, but not get blinded by the code and coding process so that they forget the logic.

The syntactic structures of XHTML are of two types: block and inline. It's important to know the difference, because you can't put block elements inside inline elements. Notice that:

• Block elements can all contain Inline elements; many can contain other block elements.
• Inline elements can only contain text or other Inline elements.

Block Structures

This table shows the elements defined as Block Structures in the formal XHTML documentation.

Notes:

• Click any element name to see its official definition.
• The symbol "|" is used to mean "or".
• "Text" is an intentional simplification of the formal PCDATA specification.
• "Inline" means this element can contain any Inline element
• Other terms, such as Heading and List, represent types of block elements that can be included.

Inline Structures

And here are the elements defined as Inline Structures:

Data in computers is of two types:

1. Information
2. Role, or "metadata"

Information is the "payload". It's what you want to get out of the computer or network. This is what we call the content of a Website.

Metadata is data about information. Its purpose is to clarify what the information is about.

For example, if you want to know someone's address, the information content is
      1234 Main St.
      Anytown
      MH
      12345

The metadata, or role, of each piece of information is
      Street
      City
      State
      Zipcode

In normal human conversation, we often get the information without its role, and supply the metadata from the context and from our experience. Since machines can't do that, we have to supply the metadata to enable software agents to understand what they're finding and use it in helpful ways.

The main purpose of RDF is to enable machine-readable metadata.

Information comes to us in many forms. On the Web, there are three main forms of content:

1. Text: plain writing
2. References: the hyperlinks to other information
3. Objects: graphics, images, applets, and many kinds of files for which plugins are required

When we talk about presentation, we're actually including two aspects of how information is brought to a human:

• Medium: the type of device through which the information comes.
• Format: the details of how content will be presented.

With the Web, normal computers (desktops and laptops) with color screens are the default medium.

Many other media exist, including PDAs and cell phones. Their popularity is making them very interesting to information providers. The ability to present Web pages on large and small screens, and even over a voice telephone, is one of the main reasons we need to separate content from presentation.

However, the primary medium for delivery of Web pages is still the normal computers.

Format includes features such as fonts and colors.

If the medium is voice, it would include relative pitch and loudness.