Metadata and XML
What is metadata?
In the computer world, information collected on objects or data is commonly referred to as “Metadata”. While many definitions exist for this term, the general consensus is to say that Metadata is “Data bout Data”. Metadata does not change anything about the item it describes but rather defines its nature but attaching a set of descriptive attributes to the object. Simple examples are the title of a book, the brand or the color of a car, the name of a person, the number of calories of a food item, etc.
An important aspect of metadata is that it can be stored, accessed or exchanged with having to pass along the underlying objects. We can browse a library catalog remotely or select a car from a brochure with going to the dealership. In a similar way, we could get describe quantum hardware, gates, circuits or algorithms with getting actual access to a real quantum computer, whether it exists or not.
What is the eXtensible Markup Language (XML)?
Nowadays, information systems commonly capture metadata using a format called the Extensible Markup Language or XML. It is a system that “tags” or “markups” elements of information and stores them in a standard text format that can be read by any computer. XML is used everywhere on the Web, in particular to exchange information between organizations. It has emerged in recent years as a dominant technology. While invisible to most end users, XML is driving today's' Internet.
XML is actually a term that encompasses several technologies and functionalist. Adopting XML as a common language allows information systems not only to capture metadata (in XML) but also to validate it against agreed upon specifications (using DTD or XSchema), transform it to other formats such as HTML or PDF(using XSLT), search it to build catalogs and lookup information (using XPath or XQuery), exchange it (using SOAP based web services) and even edit it (using XForms). All these functionalist are inherent to the XML technology and require little efforts to implement.
See the Resources section of this site for links to XML related web sites, tutorials and tools.