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At an idealized level, XML is a generic syntax that is amenable to a wide variety of contexts and domains. Its utility is attributable to the following qualities: 1) It is text based Labels, delimiters, and content are encoded as Unicode characters. Consequence: There are few impedements to transfering XML data across heterogenous system boundaries. XML documents can be created using simple text editors. 2) It is well-formed The syntax can be interpreted unambiguously and without reliance upon rules of inference. Consequence: XML parsers are simple and ubiquitous. 3) It is partially self-describing All content (data) is labeled. Consequence: Content type can be clearly identified, both by human and machine. However, semantics are implicit. 4) It is structured The syntax describes a single-rooted tree. Consequence: Most real-world content maps well to hierarchies; hierarchies are also readily grasped by human beings. Thus, XML documents tend to be human-readable. At a practical level, XML has some warts: 1) It is text based Consequence: Not all data is efficiently encoded as characters. 2) It is well-formed Consequence: Well-formedness is wordy. 3) It is partially self-describing Consequence: Names alone are often not sufficient to unambigously convey semantics. 4) It is structured Consequence: Data retrieval from trees is not always efficient. Some data cannot be naturally modeled hierarchically.
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