HTML versus XML- Dr. Jawad Makki

HTML versus XML: Similarities

• Both use tags(e.g. <h2> and </year>) 
• Tags may be nested (tags within tags)
• Human users can read and interpret both HTML and XML representations quite easily

… But how about machines?


Problems with Automated Interpretation of HTML Document

An intelligent agent trying to retrieve the names of the authors of the book

• Authors’ names could appear immediately after the title
• or immediately after the word by 
• Are there two authors?
• Or just one, called “V. Marek and M. Truszczynski”?

HTML vs XML: Structural Information

• HTML documents do not contain structural information: pieces of the document and their relationships.
• XML more easily accessible to machines because

1. Every piece of information is described.
2. Relations are also defined through the nesting structure.
3. E.g., the <author>tags appear within the <book>tags, so they describe properties of the particular book.

• A machine processing the XML document would be able to deduce that

1. the authorelement refers to the enclosing bookelement
2. rather than by proximity considerations

• XML allows the definition of constraints on values

1. E.g.a year must be a number of four digits

HTML vs XML: Formatting

1. The HTML representation provides more than the XML representation:

• The formatting of the document is also described

      2. Τhe main use of an HTML document is to display information: it must define formatting

      3. XML: separation of content from display

• same information can be displayed in different ways