when should i go for Expat parser rather Dom Parser and vice versa ? What is the difference between these parsers ?
The xml_parser_ functions give you a stream of SAX-style callbacks as the file is consumed. It's up to you to handle or store them appropriately as they come in, linearly in document order.
(XMLReader is another serial-access parser with an imperative rather than event-based interface, which can be useful particularly for more rigidly-defined data formats.)
The DOMDocument loaders read the entire XML content into memory and give you a simple object-like means of querying any part of the document. For random-access tasks this is much easier to cope with, but it's also much less efficient for large documents.
Expat is a SAX parser.
Here's a comparison between SAX and DOM parser
SAX:
Does not load the XML into memory
Top to bottom traversing
Event driven and works incrementally.
DOM:
Loads XML into memory. Hence occupies more memory.
Traverse in any direction.
Related
I have two identical webpages aside from the php code. One uses SimpleXML and the other uses DOMDocument. The code edits xml files (reading, adding nodes, removing nodes).
With SimpleXML I must remove nodes using:
unset($node);
With DOMDocument, however, I use:
$node->parentNode->removeChild($node)
While the SimpleXML seems advantageous due to its brevity, it ends up taking an additional 0.4 seconds to load the page that uses SimpleXML (both pages have the same # of php lines).
What is the reason behind this performance difference? Is it the unset() function that bogs it down?
SimpleXML is an abstraction on same DOM XML library that the DOM implementation itself uses. But it is an abstraction implemented in C. That means here will be situations where SimpleXML is faster because it combines several actions on the C level and others where it is slower because it just adds syntax sugar.
If you do a lot of manipulations on an XML, using XSLT might be an even faster solution.
Like all optimization you should measure and decide.
Which is the optimal way of XML parsing(XML may be of large amount of data) in php?
See XML and PHP 5 in Devzone for a good introduction.
Basically, if you need to process large volumes of XML files, you will want to use a pull parser, like XMLReader or XMLParser to prevent running into memory issues. Parser like DOM or SimpleXML will read the whole files into memory before you can process them.
one of the most common ways is SimpleXML. it's pretty easy to use and fast.
i've used SAXY XML parser in the past. try it.
If you need a way to parse XML data that is valid for PHP4 too, then you can use the XML parser, or DOM XML (which is a PHP4 only extensions); if you need a solution for PHP5, then you can use DOM, or XMLReader.
It depends from your needs.
I am testing various methods to read (possibly large, with very frequent reads) XML configuration files in PHP. No writing is ever needed. I have two successful implementations, one using SimpleXML (which I know is a DOM parser) and one using XMLReader.
I know that a DOM reader must read the whole tree and therefore uses more memory. My tests reflect that. I also know that A SAX parser is an "event-based" parser that uses less memory because it reads each node from the stream without checking what is next.
XMLReader also reads from a stream with the cursor providing data about the node it is currently at. So, it definitely sounds like XMLReader (http://us2.php.net/xmlreader) is not a DOM parser, but my question is, is it a SAX parser, or something else? It seems like XMLReader behaves the way a SAX parser does but does not throw the events themselves (in other words, can you construct a SAX parser with XMLReader?)
If it is something else, does the classification it's in have a name?
XMLReader calls itself a "pull parser."
The XMLReader extension is an XML Pull parser. The reader acts as a cursor going forward on the document stream and stopping at each node on the way.
It later goes on to say it uses libxml.
This page on Java XML Pull Parsing may be of some possible interest. If XMLReader is related to this project's goals and intent, then the answer to your question falls squarely into the "neither" category.
A SAX parser is a parser which implements the SAX API. That is: a given parser is a SAX parser if and only if you can code against it using the SAX API. Same for a DOM parser: this classification is purely about the API it supports, not how that API is implemented. Thus a SAX parser might very well be a DOM parser, too; and hence you cannot be so sure about using less memory or other characteristics.
However to get to the real question: XMLReader seems the better choice because since it is a pull parser you request the data you want quite specifically and therefore there should be less overhead involved.
XMLReader is an interface that a SAX2 parser must implement. Thus you could say that you have a SAX parser when you access it through XMLReader and for short that XMLReader is the SAX parser.
See the javadoc of XMLReader.
XMLReader is the interface that an XML parser's SAX2 driver must implement. This interface allows an application to set and query features and properties in the parser, to register event handlers for document processing, and to initiate a document parse.
I think this information is relevant because:
It comes from the official Web site for SAX
Even if the javadoc is for Java, SAX originated in the Java language.
In short, it is neither.
SAX parsers are stream-oriented, event-based push parsers. You register callback functions to handle events such as startElement and endElement, then call parse() to process the entire XML document, one node at a time. To my knowledge, PHP doesn't have a well-maintained SAX parser. However, there is XMLParser, which uses the very similar Expat library.
DOM parsers require you to load the entire XML document into memory, but they provide an object-oriented tree of the XML nodes. Examples of DOM parsers in PHP include SimpleXML and DOM.
The PHP XMLReader is neither of these. It is a stream-oriented "pull parser" that requires you to create a big loop and call the read() function to move the cursor forward, processing one node at a time.
The big benefit of XMLParser and XMLReader vs SimpleXML and DOM is that stream-oriented parsers are memory efficient, only loading the current node into memory. On the other hand, SimpleXML and DOM are easier to use, but they require you to load the entire XML document into memory, and this is bad for very large XML documents.
The original question is below, but I changed the title because I think it will be easier to find others with the same doubt. In the end, a XHTML document is a XML document.
It's a beginner question, but I would like to know which do you think is the best library for parsing XHTML documents in PHP5?
I have generated the XHTML from HTML files (which where created using Word :S) with Tidy, and know I need to replace some elements from them (like the and element, replace some attributes in tags).
I haven't used XML very much, there seems to be many options for parsing in PHP (Simple XML, DOM, etc.) and I don't know if all of them can do what I need, an which is the easiest one to use.
Sorry for my English, I'm form Argentina. Thanks!
I bit more information: I have a lot of HTML pages, done in Word 97. I used Tidy for cleaning and turning them in XHTML Strict, so now they are all XML compatible. I want to use an XML parser to find some elements and replace them (the logic by which I do this doesn't matter). For example, I want all of the pages to use the same CSS stylesheet and class attributes, for unified appearance. They are all static pages which contains legal documents, nothing strange there. Which of the extensions should I use? Is SimpleXML enough? Should I learn DOM in spite of being more difficult?
You could use SimpleXML, which is included in a default PHP install. This extensions offers easy object-oriented access to XML-structures.
There's also DOM XML. A "downside" to this extension is that it is a bit harder to use and that it is not included by default.
Just to clear up the confusion here. PHP has a number of XML libraries, because php4 didn't have very good options in that direction. From PHP5, you have the choice between SimpleXml, DOM and the sax-based expat parser. The latter also existed in php4. php4 also had a DOM extension, which is not the same as php5's.
DOM and SimpleXml are alternatives to the same problem domain; They læoad the document into memory and let you access it as a tree-structure. DOM is a rather bulky api, but it's also very consistent and it's implemented in many languages, meaning that you can re-use your knowledge across languages (In Javascript for example). SimpleXml may be easier initially.
The SAX parser is a different beast. It treats an xml document as a stream of tags. This is useful if you are dealing with very large documents, since you don't need to hold it all in memory.
For your usage, I would probably use the DOM api.
DOM is a standard, language-independent API for heirarchical data such as XML which has been standardized by the W3C. It is a rich API with much functionality. It is object based, in that each node is an object.
DOM is good when you not only want to read, or write, but you want to do a lot of manipulation of nodes an existing document, such as inserting nodes between others, changing the structure, etc.
SimpleXML is a PHP-specific API which is also object-based but is intended to be a lot less 'terse' than the DOM: simple tasks such as finding the value of a node or finding its child elements take a lot less code. Its API is not as rich than DOM, but it still includes features such as XPath lookups, and a basic ability to work with multiple-namespace documents. And, importantly, it still preserves all features of your document such as XML CDATA sections and comments, even though it doesn't include functions to manipulate them.
SimpleXML is very good for read-only: if all you want to do is read the XML document and convert it to another form, then it'll save you a lot of code. It's also fairly good when you want to generate a document, or do basic manipulations such as adding or changing child elements or attributes, but it can become complicated (but not impossible) to do a lot of manipulation of existing documents. It's not easy, for example, to add a child element in between two others; addChild only inserts after other elements. SimpleXML also cannot do XSLT transformations. It doesn't have things like 'getElementsByTagName' or getElementById', but if you know XPath you can still do that kind of thing with SimpleXML.
The SimpleXMLElement object is somewhat 'magical'. The properties it exposes if you var_dump/printr/var_export don't correspond to its complete internal representation. It exposes some of its child elements as if they were properties which can be accessed with the -> operator, but still preserves the full document internally, and you can do things like access a child element whose name is a reserved word with the [] operator as if it was an associative array.
You don't have to fully commit to one or the other, because PHP implements the functions:
simplexml_import_dom(DOMNode)
dom_import_simplexml(SimpleXMLElement)
This is helpful if you are using SimpleXML and need to work with code that expects a DOM node or vice versa.
PHP also offers a third XML library:
XML Parser (an implementation of SAX, a language-independent interface, but not referred to by that name in the manual) is a much lower level library, which serves quite a different purpose. It doesn't build objects for you. It basically just makes it easier to write your own XML parser, because it does the job of advancing to the next token, and finding out the type of token, such as what tag name is and whether it's an opening or closing tag, for you. Then you have to write callbacks that should be run each time a token is encountered. All tasks such as representing the document as objects/arrays in a tree, manipulating the document, etc will need to be implemented separately, because all you can do with the XML parser is write a low level parser.
The XML Parser functions are still quite helpful if you have specific memory or speed requirements. With it, it is possible to write a parser that can parse a very long XML document without holding all of its contents in memory at once. Also, if you not interested in all of the data, and don't need or want it to be put into a tree or set of PHP objects, then it can be quicker. For example, if you want to scan through an XHTML document and find all the links, and you don't care about structure.
I prefer SimpleXMLElement as it's pretty easy to use to lop through elements.
Edit: It says no version info avaliable but it's avaliable in PHP5, at least 5.2.5 but probably earlier.
It's really personal choice though, there's plenty of XML extensions.
Bear in mind many XML parsers will balk if you have invalid markup - XHTML should be XML but not always!
It's been a long time (2 years or more) since I worked with XML parsing in PHP, but I always had good, usable results from the XML_Parser Pear package. Having said that, I have had minimal exposure to PHP5, so I don't really know if there are better, inbuilt alternatives these days.
I did a little bit of XML parsing in PHP5 last year and decided to use a combination of SimpleXML.
DOM is a bit more useful if you want to create a new XML tree or add to an existing one, its slightly more flexible.
It really depends on what you're trying to accomplish.
For pulling rather large amounts of data, I.E many records of say, product information from a store website, I'd probably use Expat, since its supposedly a bit faster...
Personally, I've has XML's large enough to create a noticeable performance boost.
At those quantities you might as well be using SQL.
I recommend using SimpleXML.
It's pretty intuitive, easy to use/write.
Also, works great with XPath.
Never really got to use DOM much, but if you're using the XML Parser for something as large as you're describing you might want to use it, since its a bit more functional than SimpleXML.
You can read about all three at W3C Schools:
http://www.w3schools.com/php/php_xml_parser_expat.asp
http://www.w3schools.com/php/php_xml_simplexml.asp
http://www.w3schools.com/php/php_xml_dom.asp
I like the XMLReader class for it's simplicity and speed. But I like the xml_parse associated functions as it better allows for error recovery. It would be nice if the XMLReader class would throw exceptions for things like invalid entity refs instead of just issuinng a warning.
I'd avoid SimpleXML if you can. Though it looks very tempting by getting to avoid a lot of "ugly" code, it's just what the name suggests: simple. For example, it can't handle this:
<p>
Here is <strong>a very simple</strong> XML document.
</p>
Bite the bullet and go to the DOM Functions. The power of it far outweighs the little bit extra complexity. If you're familiar at all with DOM manipulation in Javascript, you'll feel right at home with this library.
SimpleXML seems to do a good job for me.
SimpleXML and DOM work seamlessly together, so you can use the same XML interacting with it as SimpleXML or DOM.
For example:
$simplexml = simplexml_load_string("<xml></xml>");
$simplexml->simple = "it is simple.";
$domxml = dom_import_simplexml($simplexml);
$node = $domxml->ownerDocument->createElement("dom", "yes, with DOM too.");
$domxml->ownerDocument->firstChild->appendChild($node);
echo (string)$simplexml->dom;
You will get the result:
"yes, with DOM too."
Because when you import the object (either into simplexml or dom) it uses the same underlining PHP object by reference.
I figured this out when I was trying to correct some of the errors in SimpleXML by extending/wrapping the object.
See http://code.google.com/p/blibrary/source/browse/trunk/classes/bXml.class.inc for examples.
This is really good for small chunks of XML (-2MB), as DOM/SimpleXML pull the full document into memory with some additional overhead (think x2 or x3). For large XML chunks (+2MB) you'll want to use XMLReader/XMLWriter to parse SAX style, with low memory overhead. I've used 14MB+ documents successfully with XMLReader/XMLWriter.
There are at least four options when using PHP5 to parse XML files. The best option depends on the complexity and size of the XML file.
There’s a very good 3-part article series titled ‘XML for PHP developers’ at IBM developerWorks.
“Parsing with the DOM, now fully compliant with the W3C standard, is a familiar option, and is your choice for complex but relatively small documents. SimpleXML is the way to go for basic and not-too-large XML documents, and XMLReader, easier and faster than SAX, is the stream parser of choice for large documents.”
I mostly stick to SimpleXML, at least whenever PHP5 is available for me.
http://www.php.net/simplexml