Introduction to XML Versions
The abbreviation of XML is eXtensible Markup Language, it is a markup language which is similar to HTML and it is basically designed to transport and store data and it is mostly self-descriptive like it has the information of the sender, has the information from the receiver, has a heading and also contains a body with message but still, nothing is done by XML, it is just information covered in tags, it does not contain any predefined tags and it is expected to work in the same way even when there is change of data that is even if new data is added or existing data is removed. In this article, we will discuss different XML versions.
Various XML Versions
There are two versions of XML, they are:
1) XML 1.0
XML was developed in 1996 by a working group of worldwide web consortium with several design goals. They are:
- XML must be used straightforward on the internet.
- Different varieties of applications must be supported by XML.
- There should be compatibility between XML and SGML.
- Programs to process XML documents must be easy to write.
- Optional features in XML should be zero.
- The documents of XML must be easy to understand.
- The design of XML should not take more time.
- The design of XML should be concise and formal.
- The documents created in XML should be easy.
The terminology used to build the definitions and to describe the XML processor actions are:
- Must not
- Shall not
- Should not
- Fatal error
- At user option
- Validity constraint
- Well-formedness constraint
- For compatibility
- For interoperability
A well-formed data object is called an XML document. A textual object becomes a well-formed XML document if it satisfies the below criteria:
- It should match the labeled document in the production.
- All the constraints of well-formedness must be met.
- The directly or indirectly referenced parsed entities form a well-formed document.
The markup or character data is represented by a sequence of characters called text. The mixture of name characters is called Nmtoken. A name becomes a Nmtoken if it consists of initial characters that belong to the restricted set. The validity of the attribute values that are tokenized after normalization can be defined using Names and Nmtokens.
Anything that is at the higher level of the document like end tags, references of an entity, references of characters, etc. constitutes mark up. The statements that can be outside the markup but anywhere in the document are called comments. The instructions for applications are contained in documents which are allowed by processing instructions. Some of the text blocks consisting of characters can be recognized as mark up. In order to avoid that CDATA sections are used to escape these text blocks.
Grammar is necessary for the documents class and this grammar is provided by mark up declarations present in document type declaration. Declaration of the element type, declaration of the attribute type, declaration of entity or declaration of notation is called markup declaration. To enable good readability of markup, white spaces are used in XML. These white spaces will not be included in the document which is in the delivered version. One or more elements are present in an XML document and start tags, end tags, empty tags are used to delimit these elements and a generic identifier is used to identify each element.
A start tag is used to indicate the starting of a non-empty XML element. If an element of a type consists of children or also called child elements, then we say the element consists of the element content. If an element of a type consists of character data along with children or also called child elements, then we say the element consists of mixed content. The elements are associated with pairs of names and values called attributes. There are three types of attributes in XML. They are string types that take literal value strings, tokenized types set which are more restricted and enumerated types. To decide if an attribute is required or not, an attribute declaration is necessary. Entities are more than one unit of storage in XML documents.
2) XML 1.1
The features of XML 1.1 are similar to XML 1.0 except for a few of the changes. Those changes are:
- The names in XML 1.1 are designed in such a way that whatever is not forbidden is permitted.
- NEL (#x85) is one of the line end characters and is supported by XML 1.1.
- #X2028 is a line separator character and is supported by XML 1.1.
- The control characters from #x1 to #x1F are not permitted in XML 1.0 but XML 1.1 provides character references to these control characters.
- A set of constraints is defined by XML 1.1 which is called XML documents full normalization. The creators of documents must make sure the documents created abide by the set of constraints defined for full normalization and this should be cross-checked by the processors of documents.
- The version difference between the XML 1.0 and XML 1.1 is provided in the XML declaration at the beginning of the document and it is represented by the information of version number.
- All the XML documents in XML 1.0 are well formed in XML 1.1 but the XML documents in XML 1.1 is not well formed in XML 1.0.
- XML 1.0 supports different languages like English, Dutch, German, etc. but if we are using a language that consists of too many special characters, then XML 1.1 is preferred.
Extensible Markup Language acts as a foundation for the creation of documents and systems of documents. The operations of Extensible Markup Language happen in two levels, the first level is syntax is provided for the mark up of documents. The second level is syntax is provided for the declaration of structures of documents. The target of Extensible Markup Language is web but the applications of Extensible Markup Language go beyond the scope of web. Learning HTML is not a prerequisite to learn XML but those who have worked with HTML before can find learning Extensible Markup Language easier.