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+* XML Classes
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+
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+** Abstract
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+
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+ XML library is used by several field of Mono such as ADO.NET and XML
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+ Digital Signature (xmldsig). Here I write about System.Xml.dll and
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+ related tools. This page won't include any classes which are in other
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+ assemblies such as XmlDataDocument.
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+
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+ Note that current corlib has its own XML parser class named Mono.Xml.MiniParser.
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+
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+ Basically System.XML.dll feature has finished, or almost finished, so
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+ I write this page mainly for bugs and improvement hints.
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+
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+
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+** System.Xml namespace
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+
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+
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+*** Document Object Model (Core)
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+
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+ DOM feature has already implemented. There is still missing feature.
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+
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+ <ul>
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+ * ID constraint support is problematic because W3C DOM does not specify
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+ handling of ID attributes into non-adapted element. (MS.NET also
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+ looks incomplete in this area).
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+
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+ * I think, event feature is not fully tested. There are no concrete
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+ desctiption on which events are risen, so we have to do some
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+ experiment on MS.NET.
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+ </ul>
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+
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+*** Xml Writer
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+
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+ Here XmlWriter almost equals to XmlTextWriter. If you want to see
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+ another implementation, check XmlNodeWriter.cs used in monodoc.
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+
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+ XmlTextWriter is completed. However, it looks nearly twice as slow as
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+ MS.NET (I tried 1.1)
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+
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+*** XmlResolver
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+
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+ Currently XmlTextReader uses specified XmlResolver. If nothing was supplied,
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+ then it uses XmlUrlResolver. XmlResolver is used to parse external DTD,
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+ importing XSL stylesheets and schemas etc.
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+
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+ However, XmlUrlResolver is still buggy (mainly because System.Uri is also
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+ incomplete yet) and this results in several loading error.
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+
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+ XmlSecureResolver, which is introduced in MS .NET Framework 1.1 is basically
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+ implemented, but it requires CAS (code access security) feature. We need to
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+ fixup this class after ongoing CAS effort works.
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+
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+
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+*** XmlNameTable
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+
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+ XmlNameTable itself is implemented. However, it should be actually used in
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+ several classes. Currently it makes sense if compared names are both in
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+ the table, but if it is obvious that compared names are both in this table,
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+ it should be simply compared using ReferenceEquals() (if these names are
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+ different, the comparison is still inefficient yet).
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+
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+
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+*** Xml Stream Reader
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+
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+ When we are using ASCII document, we don't care which encoding we are using.
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+ However, XmlTextReader must be aware of the specified encoding in XML
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+ declaration. So we have internal XmlStreamReader class (and currently
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+ XmlInputStream class. This may disappear since XmlStreamReader is enough to
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+ handle this problem).
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+
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+ However, there are some problems lies in these classes on reading network
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+ stream (especially on Linux). This should be fixed soon.
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+
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+
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+*** XML Reader
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+
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+ XmlTextReader, XmlNodeReader and XmlValidatingReader are almost finished.
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+
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+ - Most of the OASIS conformance test passes as Microsoft does, but
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+ about W3C tests, it is not perfect.
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+
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+ - I won't add any XDR support on XmlValidatingReader. (I haven't
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+ ever seen XDR used other than Microsoft's BizTalk Server 2000,
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+ and Now they have 2003 with XML Schema support)
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+
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+ XmlTextReader and XmlValidatingReader should be faster than now. Currently
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+ XmlTextReader looks nearly twice as slow as MS.NET, and XmlValidatingReader
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+ (which uses this slow XmlTextReader) looks nearly three times slower. (Note
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+ that XmlValidatingReader won't be slow as itself. It uses schema validating
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+ reader and dtd validating reader.)
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+
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+
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+**** Some Advantages
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+
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+ The design of Mono's XmlValidatingReader is radically different from
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+ that of Microsoft's implementation. Under MS.NET, DTD content validation
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+ engine is in fact simple replacement of XML Schema validation engine.
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+ Mono's DTD validation is designed fully separate and does validation
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+ as normal XML parser does. For example, Mono allows non-deterministic DTD.
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+
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+ Another advantage of this XmlValidatingReader is support for *any* XmlReader.
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+ Microsoft supports only XmlTextReader.
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+
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+ I added extra support interface named "IHasXmlParserContext", which is
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+ considered in XmlValidatingReader.ResolveEntity(). Microsoft failed to
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+ design XmlReader to support pluggable use of XmlReader (i.e. wrapping use
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+ of other XmlReader) since XmlParserContext is required to support both
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+ entity resolution and namespace manager. (In .NET 1.2, Microsoft also
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+ supported similar to IHasXmlParserContext, named IXmlNamespaceResolver,
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+ but it still does not provide any DTD information.)
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+
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+ We also have RELAX NG validating reader. See mcs/class/Commons.Xml.Relaxng.
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+
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+
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+** System.Xml.Schema
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+
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+*** Schema Object Model
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+
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+ Basically it is implemented. Some features still needs to fix:
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+
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+ - Complete facet support. Currently some of them is missing. Recently
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+ David Sheldon is doing several fixes on them.
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+
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+ - Complete derivation by restriction (DBR) support. Especially
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+ substitution group won't work with it (However, I won't recommend
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+ both substitution group and DBR, regardless of this incompleteness.)
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+
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+ Some bugs are remaining, but as far as I tried W3C XML Schema test suite
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+ with bugfixes (of test suite), only 69 out of 7581 has failed. With my test
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+ suite fix, MS.NET failed 48 cases.
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+
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+*** Validating Reader
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+
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+ XML Schema validation feature is (currently) implemented on
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+ Mono.Xml.Schema.XsdValidatingReader, which is internally used in
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+ XmlValidatingReader.
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+
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+ Basically this is implemented and actually its feature is almost complete,
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+ but I have only did validation feature testing. So we have to write more
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+ tests on properties, methods, and events (validation errors).
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+
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+
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+** System.Xml.Serialization
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+
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+ Lluis rules ;-)
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+
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+ Well, in fact XmlSerializer is almost finished and is on bugfix phase.
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+ However, more tests are required especially schema import and export
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+ feature. Please try xsd.exe to create classes from schema, or schema
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+ from class. And if any problems were found, please file it to bugzilla.
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+
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+
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+** System.Xml.XPath and System.Xml.Xsl
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+
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+ There are two implementations for XSLT. One (and historical) implementation
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+ is based on libxslt. Now we uses fully implemented managed XSLT.
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+
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+ Putting aside bug fixes, we have to support:
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+
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+ - embedded script (such as VB, C#, JScript). So some packages like
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+ latest NAnt (for MS.NET) won't be compiled.
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+
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+ It would be nice if we can support <a href="http://www.exslt.org/">EXSLT</a>.
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+ <a href="http://msdn.microsoft.com/WebServices/default.aspx?pull=/library/en-us/dnexxml/html/xml05192003.asp">Microsoft has already done it</a>, but it
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+ is not good code since it depends on internal concrete derivatives of
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+ XPathNodeIterator classes. In general, .NET's "extension objects" is not
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+ usable to return node-sets, so if we support EXSLT, it has to be done
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+ internally inside our System.XML.dll. Volunteers are welcome.
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+
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+ Our managed XSLT implementation is still inefficient. XslTransform.Load()
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+ and .Transform() looks three times slower (However it depends on
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+ XmlTextReader which is also slow, so we are starting optimization from
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+ that class, not XSLT itself). These number are only for specific cases,
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+ and there might be more critical point on XSLT engine (mainly
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+ XPathNodeIterator).
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+
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+
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+** Miscellaneous Class Libraries
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+
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+*** RELAX NG
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+
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+ I implemented an experimental RelaxngValidatingReader. It is far from
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+ complete, especially simplification stuff (see RELAX NG spec chapter 4),
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+ some constraints (in chapter 7), and datatype handling.
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+
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+ I am planning improvements (starts with renaming classes, giving more
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+ kind error messages, supporting compact syntax and even object mapping),
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+ but it is still my wishlist.
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+
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+
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+** Tools
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+
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+*** xsd.exe
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+
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+ xsd.exe is used to:
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+
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+ 1) generate classes source code from schema
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+ 2) generate DataSet classes source code from schema
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+ 3) generate schema documents from assembly (classes)
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+ 4) infer schema documents from XML instance
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+ 5) convert XDR into XSD
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+
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+ As descrived above, I won't work on 5) XDR stuff.
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+
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+ Current xsd.exe supports 1) and 3)
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+
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+ As for 2) and 4), Currently there is no works on them. (This inference
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+ feature is rather DataSet specific than general purpose use.)
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+
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+ Microsoft has another inference class from XmlReader to XmlSchemaCollection.
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+ It may be useful, but it won't be so easy.
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+
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+ any volunteers?
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+
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Atsushi Eno