This short article will take a look at a few of the more complex approaches to dealing with schema design, thus this post is only suitable for people that have a good understanding of xml and xml schema. If you are a newcomer to xml you need to first acquaint yourself with the fundamentals of xml schema, the w3c school site is a superb place to begin in that respect.
For all those who've been developing for years, you could remember that historically when you wanted to verify your xml data, you had to employ a technique also known as Document Type Definition (DTD).
Practically everyone loathed working with DTD’s because they were so difficult to work with and even more tough to figure out with their alien like syntax and symbols. It’s not really unpredictable that so many folks gave up on using DTD’s to validate xml seeing that it took so much time and was so difficult that many were unable to write correct DTDs.
Thankfully, the W3C realised that DTD was not supporting the cause of xml, as they were very eager for xml to develop into the standard for markup, in particular with regards to digital and the internet.
The W3C solution was to come up with a brand-new way to validate xml, named Xml Schema. It was a much less difficult option for validating your xml and also gave developers the exact same capabilities as DTD but enhanced it substantially making it far more maintainable and extensible.
The schema serves as a blueprint for your xml file, laying down what can and also can't be included in your xml document, for instance what elements and attributes are permitted within your xml document, the values involved with those elements, the order and occurrence and so on. Which means that it’s relatively a lot like a DTD but unlike a DTD, with a schema you can in addition handle data typing, inheritance, database linkage and grouping.
The W3C Working Group at the same time introduced the notion of “document instances” that permits you to connect specific xml documents to a schema and validate your xml document against the rules in the schema.
The specs put forth by the W3C Working Group, most importantly creates a differentiation between “simple” and “complex” elements. This has fundamental considerations for programmers, simple elements can not have other elements or attributes, whereas complex elements can. Complex elements might also function as containers for other elements, that could be either simple or complex elements.
In making your xml schema, a simple type element is expressed by the <xsd:simpleType> and a complex type element is expressed by the <xsd:complexType> statement.
To be able to present simple elements in your schema, the correct way might be to use the <xsd:element> statement.
Regarding complex types, we have an additional step further than declaring the complex type, you ought to declare the type through the element, give it a name and then use this new type in the same <xsd:element> statement as per a simple element.
I really hope this article has given you some insight into xml and xml schemas, you can find out more information at w3c or w3c schools, both of which are excellent resources for grasping xml and comprehending the standard.
