The application spectrum

XML is useful both for human beings and computers. Common scenarios in which XML can be used by people include:

• writing a document using DocBook. Docbook is an XML application designed for the markup of texts mainly about computer hardware and software.
• writing a document in TEI. TEI is an XML application to markup machine-readable texts chiefly in the humanities, social sciences and linguistics.

The resulting documents are called text-centric documents. These are XML documents usually written by humans for humans or computers to read. They are semipermanent XML documents with a lot of text and a poor structure.

Common scenarios in which XML can be used by computers include:

• data exchange. Information comes in different sources (relations, objects, documents) and it needs to be exchanged between these sources. XML might act as the common dataspeak;
• semistructured databases. Semistructured data has no regular schema. It often includes duplicated and missing information. Hence, it does not naturally fit into relational databases. XML has been proposed as the data model for semistructured data.

The resulting documents are called data-centric documents. These are XML documents usually generated by computers for other computers to read. They are transitory XML documents with a lot of raw data and a rich structure.