DOM and SAX
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DOM and SAX are two APIs for working with XML documents. DOM loads the entire XML document into memory as a tree structure, allowing manipulation of the document. SAX is event-based and reads the XML document sequentially, invoking callback functions at element boundaries. Compared to DOM, SAX uses less memory but only allows reading of the document. Both APIs are supported across many programming languages including PHP.
![Example using PHP DOM // Load xml-document $dom = new domDocument(); $dom->load("books.xml"); // Create element <book></book> $book = $dom->createElement("book"); // create element <title>some contents</title> $title = $dom->createElement("title", $_GET['title']); // <book><title>some contents</title></book> $book->appendChild($title); // Add the book under root element of "books.xml" $dom->documentElement->appendChild($book); // save $dom->save("books.xml");](https://image.slidesharecdn.com/domsax-1227528096013790-8/85/DOM-and-SAX-20-320.jpg)
DOM and SAX
- 1. DOM and SAX Jussi Pohjolainen TAMK University of Applied Sciences
- 2. DOM and SAX DOM and SAX Platform and language-independent APIs for manipulating or reading XML-documents API: Application Programming Interface, set of functions, procedures, methods, classes and interfaces DOM and SAX is implemented in most programming languages: Java, PHP..
- 3. Differences between DOM and SAX DOM SAX Standardization W3C Recommendation No formal specification Manipulation Reading and Writing (manipulation) Only Reading Memory Consumption Depends on the size of the source xml-file, can be large Very low XML handling Tree-based Event-based
- 4. SAX
- 5. Overview of SAX SAX: Simple API for XML Originally a Java – only API Nowdays SAX is supported in almost all programming languages Uses a event-driven model Quantity of memory usage is low Only for reading xml-documents
- 6. Event-driven? SAX uses event-driven model for reading xml-documents The basic idea is, that SAX parser reads the xml-document " one line at a time". Handler functions reacts when finding elements and other parts of the xml-document. When the parser finds starting tag, then a certain function is called.. when the parser winds ending tag a certain function is called
- 7. Example (Wikipedia) <?xml version="1.0" encoding="UTF-8"?> <RootElement param="value"> <FirstElement> Some Text </FirstElement> <SecondElement param2="something"> Pre-Text <Inline>Inlined text</Inline> Post-text. </SecondElement> </RootElement>
- 8. Example (Wikipedia) XML Processing Instruction, named xml, with attributes version equal to "1.0" and encoding equal to "UTF-8" XML Element start, named RootElement, with an attribute param equal to "value" XML Element start, named FirstElement XML Text node, with data equal to "Some Text" (note: text processing, with regard to spaces, can be changed) XML Element end, named FirstElement ....
- 9. PHP and SAX // Creates an XML Parser $xml_parser = xml_parser_create(); // Set up for reading xml_set_element_handler($xml_parser, "startElement", "endElement"); xml_set_character_data_handler($xml_parser, "characterData"); // Open XML file if (!($fp = fopen($file, "r"))) { die("could not open XML input"); } // Reading and Parsing xml-file while ($data = fread($fp, 4096)) { if (!xml_parse($xml_parser, $data, feof($fp))) { die(sprintf("XML error: %s at line %d", xml_error_string(xml_get_error_code($xml_parser)), xml_get_current_line_number($xml_parser))); } } xml_parser_free($xml_parser);
- 10. PHP and SAX function startElement($parser, $name, $attrs) { // Do something } function endElement($parser, $name) { // Do something } function characterData($parser, $data) { echo $data; }
- 11. Benefits of SAX Excellent API when just reading the contents of the XML – file Easy and clean API Does not require much resources (mobile devices!)
- 12. DOM
- 13. DOM The Document Object Model (DOM) is a platform- and language-independent standard object model for representing HTML or XML and related formats. W3C Recommendation Can be used for manipulating XML – documents Different versions: DOM 1, DOM 2 and DOM 3
- 14. Basic Idea behind DOM API for manipulating XML – documents DOM loads xml-document into memory and creates a tree-model of the xml-data. Can consume memory, if documents are large
- 15. Tree and Nodes Tree consists of nodes Node can be Element (Element) Text (Text) Attribute (Attr) CDATA (CDATASection) Comment (Comment) Etc
- 16. Nodes and Relationships Node has references to it's first child (firstChild) last child (lastChild) next sibling (nextSibling) previous sibling (previousSibling) parent (parentNode
- 17. Node's contents Some nodes have contents (nodeValue) Attribute's value Element's value (text) Comment's value (text) etc
- 18. Collections NodeList (List of nodes) length item ( index ) NamedNodeMap (List of attributes) getNamedItem( name ) item ( index )
- 19. Example using PHP DOM // Load the xml - document $dom = new domDocument(); $dom->load("books.xml"); // NodeList of name-elements $listOfNodes = $dom->getElementsByTagName("name"); // Browse all nodes foreach($listOfNodes as $node) { print $node->nodeValue; }
- 20. Example using PHP DOM // Load xml-document $dom = new domDocument(); $dom->load("books.xml"); // Create element <book></book> $book = $dom->createElement("book"); // create element <title>some contents</title> $title = $dom->createElement("title", $_GET['title']); // <book><title>some contents</title></book> $book->appendChild($title); // Add the book under root element of "books.xml" $dom->documentElement->appendChild($book); // save $dom->save("books.xml");
- 21. Removing element $elements = $dom->getElementsByTagname("kirja"); $element = $elements->item(0); $children = $element->childNodes(); $child = $element->removeChild( $children->item(0) ); <kirjat> <kirja> <nimi>Tuntematon Sotilas</nimi> </kirja> <kirja> <nimi>Learn Java</nimi> </kirja> </kirjat>
- 22. PHP DOM and Encoding PHP DOM uses utf-8 internally Everything you put into xml-document using PHP DOM must be converted to utf-8. utf8_encode(..), utf8_decode(...)