XML and standard web interface
XML(eXtensible Markup Language) has boomed as an web standard format. It comes from SGML(Standard Generalized Markup Language). That means, XML is subset of SGML. Actually, SGML is so broad that it can cover almost all markup languages. This time, I want to present you the features of each of them.
At first, let's see the attributes of SGML.
- Some starting tag doesn't allow end tag. (ex: <img> tag)
- Some starting tag allows both end tag and naught. (ex: <p> tag)
- Some starting tag always needs end tag. (ex: <script> tag)
- Tags can lie in any order. (ex: you can use <b>A<i>B</b>C</i>)
- Some attributes should set a value.
- Some attributes should not be set.
- Quotation marks are available to evaluate an attribute.
SGML is really flexible but has many vulnerabilities by anonymous syntax. XML, which prevails in web technology enforced the rule to avoid such faults. The following is the advanced rule of XML.
- All tags must have end tag.
- Attaching slash(/) in the end of the tag can substitute for end tag.
- Tags must be in hierarchy structure.
- Every attributes should be evaluated.
- Quotation marks are essential to locate values of attributes.
Those rules which represent web standard resolves problems when interpreting markups (especially XHTML which is HTML in XML rules). You should keep them on your web site because the XHTML rule, the standard reduces distinct among web browsers or the other features of web service. Standard is a powerful tool for unification and you need to understand the rule in detail.