XML (Extensible Markup Language) is a language for the markup, which was created for describing the whole class of data objects that are called data-documents. This language is widely in use as an instrument for the grammar description of different languages; it also controls the propriety of the document composition and secures the xml data integration. Thus, the extensible markup language does not contain any tags, which were oriented for the markup; the XML only defines the order of their creating.
The XML causes the check-up of hierarchical correlations within the document and helps to implement the common standard in the document structure. It means that the extensible markup language may be practical for the construction of difficult informational systems, where the problem of the interchange of information between various applications and the xml data integration is very important.
One of the main advantages of the XML is that the program-applications of the XML-documents are not difficult. In addition, there are many sorts and kinds of program products, which were created specially for the work with the XML-documents. Nowadays, the extensible markup language is supportable by Microsoft Explorer, IE5, Netscape Communicator, database Oracle, DB-2 and the applications of MS-Office etc.1
The formal description of a new markup language consists of several interrelated elements:
· Specifications of the Extensible Markup Language (XML) 1.0, which determines the syntax of the language;
· Specifications of the XML Pointer Language (Xpointer) and the XML Linking Language (Xlink), which designate standard mechanisms for the link's establishment between the components of the XML-documents;
· Specifications of the Extensible Style Language (XSL), which define the mechanisms for an external presentation of the XML-documents.2
During the process of the development of the new markup language, the manufactures took into consideration advantages and disadvantages of all already existent languages and the fact that the main place of its use will be the Internet. The basic requirements were formulated in the following list:
· XML must be valid for the Internet usage;
· XML must be compatible with the SGML (the point is that the XML-document must also act as a SGML-document, without a submission of any changes or additions to it);
· The number of unnecessary qualities must be minimal or ideally equal to zero (since each XML-program must be able to read any XML-document);
· XML-documents must be readable by simple text processors;
· XML-markup must be very simple and easy to understand;
· XML must have a wide variety of applications;
· XML design must be strict, laconic and very simple to create.3
On the basis of the XML there were created a lot of programs, applications and such known and special-purposed markup languages as SMIL, CDF, MathML, XSL etc. There are also a lot of companies, which insert the XML into their program products. As you see, in a short period of time the XML became a real celebrity and its already wide popularity is still growing.