Chapter 5. Creating XML Schemas

For the previous two chapters, we've been working with DTDs. Over time, many people have complained to the W3C about the complexity of DTDs and have asked for something simpler. W3C listened, assigned a committee to work on the problem, and came up with a solution that is much more complex than DTDs ever were: XML schemas.

On the other hand, schemas are also far more powerful and precise than DTDs ever were. With schemas, not only can you specify the syntax of a document as you would with a DTD, but you also can do the following: specify the actual data types of each element's content, inherit syntax from other schemas, annotate schemas, use schemas with multiple namespaces, create simple and complex data types, specify the minimum and maximum number of times that an element can occur, create list types, create attribute groups, restrict the ranges of values that elements can hold, restrict what other schemas can inherit from yours, merge fragments of multiple schemas together, require that attribute or element values be unique, and much more.