XML is a makeup language for documents containing structured information.
- Structured information contains both content and some indication of what role that content plays.
- A markup language is a mechanism to identify structures in a document. The XML specification defines a standard way to add markup to documents.
XML&HTML
In HTML, both the tag semantics and the tag set are fixed.
XML specifies neither semantics nor a tag set and provides a facility to define tags and structural relationships between them.
Why XML?
XML was created so that richly structures documents could be used over the web.
XQuery is a powerful and convenient language designed for processing XML data. That means not only files in XML format, but also other data whose structure is similar to XML. Everything in XQuery is an expression which evaluates to a value.
A mesh of information linked up in such a way as to be easily processable by machines, on a global scale. Just as a globally linked database.
Why is for the Semantic Web?
We will find that it becomes easier to publish data in a repurposable form, so more people will want to publish data, and there will be a knock-on or domino effect.
RDF stands for Resource Description Framework and is built for the Web.
The most common daily use of metadata is to aid our discovery of things. RDF is a framework for describing and interchanging metadata.
The characteristics of RDF:
- Independence
- Inerchange: RDF statements can be converted into XML
- Scalability: RDF documents are simple, there-part records(Resource, Property, value), so they are easy to handle and look thingd up by.
- Properties are Resources
- Values can be resources
- Statement can be resources
OWL has three increasingly-expressive sublanguages: OWL Lite, OWL DL, and PWL Full.