Problems of Autogeneration Clearly the Relaxer-generated classes can (Apache web server tutorial)
Problems of Autogeneration Clearly the Relaxer-generated classes can provide useful code. However, a recurring theme in syndication is that data, especially in the wild of the Web, doesn t conform to a single, simple model. If you want a quick way of generating RSS 2.0 feeds, Relaxer can do a lot of the work for you. But outside of a very controlled environment the reader wouldn t be much use due to variation in the RSS/Atom version (and quality) of feeds. The same technique could be used to create RSS 1.0 generating code, though the handling of items would need care to ensure the individual items in the feed were consistent with there declaration in the channel s Seq element. Similarly, Atom classes could be automatically generated, although care would be needed to ensure that all the mandatory elements appear in their correct forms in the feed. Certainly a multiformat toolkit could be built up by joining together individual auto-generated classes. However, there is a good case to be made for sharing common modeling classes for all formats, and separating this from classes that look after reading (parsing) and writing (serializing) the data. Another possibility is to select a single object-oriented model, such as that of RSS 2.0 as demonstrated previously, but apply XSLT to the XML syntax it generates, to transform it to and from the other formats. The RDF Models Models are very important in RDF, to the extent that a set of RDF data is often described as a model. This can be rather confusing, especially since some of RDF s formal specifications are defined using a branch of logic called model theory. However, generally the basic idea of a model as an abstraction that demonstrates how the parts of a system fit together holds wherever the word crops up. RDF can be seen in terms of two complementary abstractions. The first of these considers the information as a number of statements of the form subject-property-object. The subject of these statements is a resource, and from this perspective each statement can be looked at as an individual fact about a resource. The properties are defined in such a way as to enable logically complex pieces of information to be expressed while still allowing manipulation of the data at the level of subject-property-object triples. The other model is that of the node and arc graph. In this model resources are nodes and the properties appear as arcs in the graph. The same information can be seen from either viewpoint, as a series of statements or as a graph. What s notable in the context of syndication is that either way the model is abstract, and XML data found in a feed is a representation of data in the model. The model itself isn t tied to any single representation and can be represented in other formats. There Is No Syntax! One source of confusion among XML developers when they first encounter RDF/XML is that the same pieces of information can be represented in very different ways. Take for example the following snippet of RDF/XML:
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