Criticism
Although XML Schema is successful in that it has been widely adopted and largely achieves what it set out to, it has been the subject of a great deal of severe criticism, perhaps more so than any other W3C Recommendation.
A good summary of the criticisms is provided by James Clark (who promotes his own alternative, RELAX NG):
- There are many surprises in the language, for example that restriction of elements works differently from restriction of attributes.
- The W3C Recommendation itself is extremely difficult to read. Most users find W3Cs XML Schema Primer much easier to understand
- XSD lacks any formal mathematical specification. (This makes it difficult to reason about schemas, for example to prove that a modification to a schema is backwards compatible.)
- XSD 1.0 provided no facilities to state that the value or presence of one attribute is dependent on the values or presence of other attributes (so-called co-occurrence constraints). This has been fixed in XSD 1.1.
- XSD offers very weak support for unordered content.
- The set of XSD datatypes on offer is highly arbitrary.
- The two tasks of validation and augmentation (adding type information and default values) should be kept separate.
Read more about this topic: XML Schema (W3C)
Famous quotes containing the word criticism:
“Homoeopathy is insignificant as an art of healing, but of great value as criticism on the hygeia or medical practice of the time.”
—Ralph Waldo Emerson (1803–1882)
“It is from the womb of art that criticism was born.”
—Charles Baudelaire (1821–1867)
“To be just, that is to say, to justify its existence, criticism should be partial, passionate and political, that is to say, written from an exclusive point of view, but a point of view that opens up the widest horizons.”
—Charles Baudelaire (1821–1867)