When working with XMLBeans in a strongly typed way (with a Schema), individual objects are created for each piece of information, usually instances of simple and complex Schema types. However, you can also access and manipulate the XML in a typeless manor. What we've done with XMLBeans is provided access to the full XML Infoset via the XmlCursor interface.
XmlCursor provides functionality very similar to the DOM, but takes a very different tact. Instead of creating an DOM Node for each element, attribute, text, etc, one may create a single XmlCursor and navigate that cursor about the XML instance, interrogating the XML: element/attr names, child/parent elements, text, comments, etc. Also, one may modify the XML by removing elements and attrs, inserting text, for example. All of this can be done by either not creating objects or reusing objects so that the number of objects needed to operate on the XML is constant, not on the order of the size of the XML like a DOM would require. The kind of interface allows an implementer of an in memory XML store more freedom to implement the internal structure which represents the XML in memory. One, for example, could simply store the XML as it was, for example, read in from disk and implement a cursor as an index into that string, parsing or modifying the parts of the string as necessary to satisfy the requests. We don't go to quite this extreme. In principle, we create one object for every leaf element or attribute and two objects for every interior element. All text for attribute values, comments, procinst's and text between element markup is stored in a single character array. We have found that creating fewer objects and batching text leads to loading the XML into memory faster as well as having a similar, if not slightly smaller, memory footprint when compared to the DOM. Also, working with cursors seems to be an easier programming model than the DOM as it does not have text nodes and is more intuitive. With respect to the synchronized access, the strongly typed schema XMLBeans objects cache values so that conversion to text does not occur until it is needed. Likewise, when modifications are made to the XML Infoset, the strongly typed data (ints, for example) are not parsed from the text until requested. In general the impact of synchronization is quite low because of the lazy approach we have taken along with the caching. As I read your question again, I realize that you may have interpreted synchronized to mean "managing data among several threads". The synchronization described refers to the fact that one may manipulate the XML via the XmlCursor or the strongly typed XMLBean classes generated from the schema, each mechanism capable of seeing the changes from the other in a tightly integrated way. With respect to building XMLBeans, we plan to remove any dependency upon the jars you mentioned. Indeed, there exists very little dependence on these. Mostly just interfaces, not any classes needed for the implementation. - Eric Vasilik -----Original Message----- From: Aleksander Slominski [mailto:[EMAIL PROTECTED] Sent: Friday, July 04, 2003 8:31 PM To: [EMAIL PROTECTED] Cc: Jakarta General List; [EMAIL PROTECTED] Subject: XMLBeans performance and source code status [Re: Proposal: XMLBeans] Cliff Schmidt wrote: >>What's compelling about XMLBeans compared to some of the other front >>runners, such as JDOM and XOM, Castor and JAXB? >> >> > >The main difference between XMLBeans and JDOM or XOM is that XMLBeans >does not create objects for each XML information item. Instead, it >provides cursor-based access to each item in the XML Infoset. It has >an architecture where, if an actual object is needed for a node, it >can be created on-demand. We found this provided great performance >benefit. > hi, i am interested to find if you have some more details on performance benefits - it seems to be very intriguing and distinguishing feature of XMLBeans. i may be missing something but i tried to find this information online without any lack (i checked http://dev2dev.bea.com/articles/hitesh_seth.jsp that is good overview but has not enough technical details and other docs): as far as i can understand actual objects are created for every XML information item? so as objects are in memory the same way as objects in DOM what performance benefits do you have in mind? do you refer to faster creation time or lower memory footprint? did you check for example on the same machine how big XML document can be loaded with XMLBeans and DOM (for example Xerces2) before running out of memory? >The biggest differences between XMLBeans and Castor or JAXB >are: >1) the goal of 100% Schema support (currently supports everything in >Schema other than redefine and substitution groups, and those features >are nearly ready), and >2) the integrated and synchronized access of the underlying XML content >with strongly typed Java classes. > did you estimate what is impact of requiring synchronized access? i am really curious why was is it required:. i can see need to share XML schemas but why to require synchronizing access to XML content? i would think that approach from java.util where collections are not thread-safe until specifically made synchronized could work here as well? >>I'd say you'd want to do as much setup before incubation as possible. >>This includes normalizing your code layout (something that didn't >>materialize for Tapestry, unfortunately) to match the other Jakarta >>projects (this will ease things if and when you transition to Maven >>builds). You probably want to check out a bit about Gump as well ... >>I can think of one person who will probably veto you until you are >>integrated into Gump. It's *exceptionally* painful to work with Gump >>at the moment, but ultimately worth it. >> >> i have question concerning Gump bit in general what is on Wiki page http://nagoya.apache.org/wiki/apachewiki.cgi?XmlBeansProposal: (...) '''(2) identify the initial source from which the subproject is to be populated''' *http://workshop.bea.com/xmlbeans/XsdUpload.jsp (...) i looked on source code and it seems that it is not possible to rebuild xbean.jar just from source and it is not clear what are dependencies? i noticed there are parts of code that depends on outside packages (like weblogic.xml.stream.XMLInputStream or com.bea.xquery) and some subpackages that are in com.bea.xml* that are in xbean.jar but not in src directory? what are plans for those pieces of code - are they also open source or XMLBeans would depend on BEA implementation classes to be on CLASSPATH to compile it? i hope XmlBeans will be actively developed as open source (in Apache or outside) so it continues to grow as it really looks like an interesting project. thanks, alek -- If everything seems under control, you're just not going fast enough. —Mario Andretti --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
