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Where the DOM operates on the document as a whole—building the full abstract syntax tree of an XML document for convenience of the user—SAX parsers operate on each piece of the XML document sequentially, issuing parsing events while making a single pass [ clarification needed ] through the input i bambini Video Sax.
The Java implementation of SAX is considered to be normative. A SAX parser only needs to report each parsing event as it happens, and normally discards almost all of that information once reported it does, however, keep some things, for example a list of all elements that have not been closed yet, in order to catch later errors such as end-tags in the wrong order. This much memory is usually considered i bambini Video Sax.
A DOM parser, in contrast, has to build a tree representation of the entire document in memory to begin with, thus i bambini Video Sax memory that increases with the entire document length. This takes considerable time and space for large documents memory allocation and data-structure construction take time. The compensating advantage, of course, is that once loaded any part of the document can be accessed in any order. Because of the event-driven nature of SAX, processing documents is generally far faster than DOM-style parsers, so long as the processing can be done in a start-to-end pass.
Many tasks, such as indexing, conversion to other formats, very simple formatting and the like can be done that way. Other tasks, such as sorting, rearranging sections, getting from a link to its target, looking up information on one element to help process a i bambini Video Sax one and the like require accessing the document structure in complex orders and will be much faster with DOM than with multiple SAX passes.
Due to the nature of DOM, streamed reading from disk requires techniques such as lazy evaluationcaches, virtual memory, persistent data structures, or other techniques one such technique is disclosed in US patent Processing XML documents larger than main memory is sometimes thought impossible because some DOM parsers do not allow it.
However, it is no less possible than sorting a dataset larger than main memory using disk space as memory to sidestep this limitation. Virtually any kind of XML validation requires access to the document in full. The most trivial example is that an attribute declared in the DTD to be of type IDREF, requires that there be only one element in the document that uses the same value for an ID attribute.
Similarly, to validate that each element has an acceptable sequence of child elements, information about what child elements have been seen for each parent must be kept until the parent closes.
Additionally, some kinds of XML processing simply require having access to the entire document. Editors and browsers likewise need to be able to display, modify, and perhaps re-validate at any time. While a SAX parser may well be used to construct such a tree initially, SAX provides no help for such i bambini Video Sax as a whole. A parser that implements SAX i. The SAX events include among others :.
Some i bambini Video Sax correspond to XML objects that are easily returned all at once, such as comments. Properly speaking, the SAX interface does not deal in elementsbut in events that largely correspond to tags. SAX parsing is unidirectional; previously parsed data cannot be re-read without starting the parsing operation i bambini Video Sax. There are many SAX-like implementations in existence. In practice, details vary, but the overall model is the same.
For example, XML attributes are typically provided as name and i bambini Video Sax arguments passed to element events, but can also be i bambini Video Sax as separate events, or via a hash table or similar collection of all the attributes. For another, some implementations provide "Init" and "Fin" callbacks for i bambini Video Sax very start and end of parsing; others don't.
The exact names for given event types also vary slightly between implementations. Note that the first line of the sample above is the XML Declaration and not a processing instruction; as such it will not be reported as a processing instruction event although some SAX implementations provide a separate event just for the XML declaration.
The result above may vary: the SAX specification deliberately states that a given section of text may be reported as multiple sequential text events.
Many parsers, for example, return separate text events for numeric character references. Thus in the example above, a SAX parser may generate a different i bambini Video Sax of events, part of which might include:. From Wikipedia, the free encyclopedia. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources.
Unsourced i bambini Video Sax may be challenged and removed. Retrieved The current version supports several programming language environments other than Java. Note: In a nutshell, SAX is oriented towards state independent processing, where the i bambini Video Sax of an element does not depend on the elements that came before. StAX, on the other hand, is oriented towards state dependent processing.
Although these tests do not show it, SAX parsers typically are faster for very large documents where the I bambini Video Sax model hits virtual memory or consumes all available memory. Categories : Application programming interfaces XML-based standards. Hidden categories: Articles needing additional references from August All articles needing additional references Wikipedia articles needing clarification from March Namespaces Article Talk.