* XML Classes Status and Tasks ** Abstract XML library is used by several areas of Mono such as ADO.NET and XML Digital Signature (xmldsig). Here I write about System.Xml.dll and related tools. This page won't include any classes which are in other assemblies such as XmlDataDocument. Note that current corlib has its own XML parser class (Mono.Xml.MiniParser). Basically System.XML.dll feature is almost finished, so I write this document mainly for bugs and improvement hints. ** Status *** System.Xml namespace **** Document Object Model (Core) DOM implementation has finished and our DOM implementation scores better than MS.NET as to the NIST DOM test results (it is ported by Mainsoft hackers and in our unit tests). **** Xml Writer Here XmlWriter almost equals to XmlTextWriter. If you want to see another implementation, check XmlNodeWriter.cs and DTMXPathDocumentWriter.cs in System.XML sources. XmlTextWriter is completed, though it looks a bit slower than MS.NET (I tried 1.1). **** XmlResolver XmlUrlResolver is implemented. XmlSecureResolver, which is introduced in MS .NET Framework 1.1 is basically implemented, but it requires CAS (code access security) feature. We need to fixup this class after ongoing CAS effort works. You might also be interested in an improved XmlCachingResolver by Ben Maurer. If even one time download is not acceptable, you can use this one. [2.0] XmlDataSourceResolver is not implemented as yet. **** XmlNameTable NameTable is implemented, but also needs performance improvement. It affects on the whole XML processing performance so much. Optimization hackings are welcome. There is also a bugzilla entry for this matter. **** XML Reader XmlTextReader, XmlNodeReader and XmlValidatingReader are almost finished. XmlTextReader and XmlValidatingReader should be faster than now. Currently XmlTextReader looks nearly twice as slow as MS.NET, and XmlValidatingReader (which uses this slow XmlTextReader) looks nearly three times slower. (Note that XmlValidatingReader wouldn't be so slow as itself. It uses schema validating reader and dtd validating reader.) **** Some Advantages The design of Mono's XmlValidatingReader is radically different from that of Microsoft's implementation. Under MS.NET, DTD content validation engine is in fact simple replacement of XML Schema validation engine. Mono's DTD validation is designed fully separate and does validation as normal XML parser does. For example, Mono allows non-deterministic DTD. Another advantage of this XmlValidatingReader is support for *any* XmlReader. Microsoft supports only XmlTextReader (this bug is fixed in .NET 2.0 beta, taking shape of XmlReader.Create()). I added extra support interface named "IHasXmlParserContext", which is considered in XmlValidatingReader.ResolveEntity(). This is now made as internal interface. Microsoft failed to design XmlReader so that XmlReader cannot be subtree-pluggable (i.e. wrapping use of other XmlReader) since XmlParserContext shoud be supplied for DTD information support (e.g. entity references cannot be expanded) and namespace manager. (In .NET 2.0, Microsoft also supported similar to IHasXmlParserContext, named IXmlNamespaceResolver, but it still does not provide DTD information.) We also have RELAX NG validating reader (described later). *** System.Xml.Schema **** Summary Basically it is completed. You can test how current schema validation engine is complete (incomplete) by using standalone test module (see mcs/class/System.XML/Test/System.Xml.Schema/standalone_tests). At least in my box, msxsdtest fails only 30 cases with bugfixed catalog - this score is better than that of Microsoft implementation. But instead, we need performance boost. There should be many points to improve schema compilation and validation. **** Schema Object Model Completed, except for some things to be fixed: **** Validating Reader Basically this is implemented and actually its feature is complete, but I have only did validation feature testing. So we have to write more tests on properties, methods, and events (validation errors). *** System.Xml.Serialization Lluis rules ;-) Well, in fact XmlSerializer is almost finished and is on bugfix phase. However, we appliciate more tests. Please try And if any problems were found, please file it to bugzilla. Lluis also built interesting standalone test system placed under mcs/class/System.Web.Services/Test/standalone. You might also interested in "genxs", which enables you to create custom XML serializer. This is not included in Microsoft.NET. See here and manpages for details. Code files are in mcs/tools/genxs. Lluis also created "sgen", that based on XmlSerializer.GenerateSerializer(). Code files are in mcs/tools/sgen. *** System.Xml.XPath and System.Xml.Xsl There are two XSLT implementations. One and historical implementation is based on libxslt (aka Unmanaged XSLT). Now we uses fully implemented and managed XSLT by default. To use Unmanaged XSLT, set MONO_UNMANAGED_XSLT environment value (any value is acceptable). As for Managed XSLT, we support msxsl:script. It would be nice if we can support EXSLT. Microsoft has tried to do some of them, but it is not successful because of System.Xml.Xsl design problem: So if we support EXSLT, it has to be done inside our System.XML.dll. Microsoft developers are also aware of this problem and some of them wish to have EXSLT support in WinFX (not whidbey). If anyone is interested in it, it would be nice. Our managed XSLT implementation is slower than MS XSLT for some kind of stylesheets, and faster for some. *** RELAX NG I implemented an experimental RelaxngValidatingReader. It is still not complete, for example some simplification stuff (see RELAX NG spec chapter 4; especially 4.17-19) and some constraints (especially 7.3). See mcs/class/Commons.Xml.Relaxng/README for details. Currently we have ** System.Xml v2.0 Microsoft released the first public beta version of .NET Framework 2.0, available from MSDN. It contains several new classes. There are two assemblies related to System.Xml v2.0; System.Xml.dll and System.Data.SqlXml.dll. Most of the important part are in System.Xml.dll (you will find that the core part of XQuery is in System.Xml.dll; For example, see some classes in MS.Internal.Xml namespace), so I'll still spot only on System.Xml.dll. Note that .NET Framework is pre-release version, so they are subject to change. Actually many of the pre-released classes vanished. System.Xml 2.0 contains several features such as: *** System.Xml 2.0 **** XmlReader/XmlWrier Factory methods In .NET 2.0, XmlTextReader, XmlNodeReader, XmlValidatingReader are obsolete and XmlReader.Create() is recommended (there is however no alternative way to create XmlNodeReader). Similarly, there are XmlWriter.Create() overloads. Currently, Microsoft's XmlWriter.Create() is unreliable and maybe there will be changes. So basically XmlWriter.Create() is supposed to be done after the next beta version of .NET 2.0. Some of XmlReader.Create() overloads are implemented, with limited XmlReaderSettings support. **** Typed XmlReader/XmlWriter In .NET 2.0, XmlReader is supposed to support strongly-typed data reading. They are based on W3C "XML Schema Datatypes" Recommendation and "XQuery 1.0 and XPath 2.0 Data Model" Working Draft. Some of XmlReader.ReadValueAsXxx() and XmlWriter.WriteValue() overloads are implemented, though incompletely. They are based on internal XQueryConvert. **** Sub-tree handling in XmlReader/XmlWriter/XPathNavigator Currently XmlReader.ReadSubtree(), XmlWriter.WriteSubtree() and XPathNavigator.ReadSubtree() are implemented, though not so stable. They are based on Mono.Xml.SubtreeXmlReader and Mono.Xml.XPath.XPathNavigatorReader classes. *** System.Xml.Schema 2.0 Since .NET 1.x is not so compliant with W3C XML Schema specification, Microsoft had to redesign System.Xml.Schema classes. We also have to change many things. 1) It does not expose XmlSchemaDatatype (except for obsolete members). Primitive types are represented as XmlSchemaSimpleType instances (thus there are ElementSchemaType, AttributeSchemaType, BaseXmlSchemaType that replace some existing properties). 2) "XQuery 1.0 and XPath 2.0 Data Model" datatypes (such as xdt:dayTimeDuration) are newly supported. They are partially implemented yet. 3) schema structures are now bound in parent-child relationship. It is not yet implemented. With related to it, there seems bunch of schema compilation bugfixes. 4) XmlSchemaCollection is not used anymore to represent effective set of schemas. Instead, new XmlSchemaSet class is used. It should affect on schema compilation design. In fact, I've implemented XmlSchemaCollection as more conformant to W3C specification, but there are still many changes required. **** XSD Inference In .NET 2.0, there is an XML Schema inference implementation. Now that XmlSchemaSet is basically implemented, it can be separately done by anyone. Volunteer efforts are welcome here. *** System.Xml.XPath 2.0 **** Editable XPathDocument in .NET 2.0 XPathDocument is supposed to be editable. Currently we provide fast document table model based implementation (DTMXPathNavigator), but by that design change, we (and they) cannot provide fast read only XPathNavigator from XPathDocument anymore. Currently, new XPathDocument implementation is provided. The actual implementation is Mono.Xml.XPath.XPathDocument2, that is simple dom-like tree model. XPathDocument2 implements the same interfaces as XPathDocument does. And XPathDocument delegates most of the methods to that class (for example, XPathDocument.CreateEditor() calls XPathDocument2.CreateEditor()). Currently Mono.Xml.XPath.XPathDocument2 is unstable (it does not pass the standalone XSLT tests as well as existing DTMXPathDocument does). So it did not replace existing XPathDocument implementation, but you can use new implementation by explicitly setting environment value USE_XPATH_DOCUMENT_2 = yes. Currently it supports (well, is supposed to support) basic editor feature such as AppendChild(). Other members are untested (such as RejectChanges()). **** extra stuff - XPathEditableDocument Currently we provide another IXPathEditable; XPathEditableDocument. That is based on the idea that handles XmlDocument as editor target. It is implemented as Mono.Xml.XPath.XPathEditableDocument. We might provide this class as extra set (might be different mono-specific XML assembly). **** System.Xml.XQuery and System.Xml.Xsl 2.0 XQuery is a new face XML data manipulation language (well, at least new face in .NET world). It is similar to SQL, but intended to manipulate and to support XML. It is similar to XPath, but extended to support new features such as XML Schema based datatypes. XQuery implementation can be found mainly in System.Xml.Query and MS.Internal.Xml.Query namespaces. The implementation is mostly in System.Xml.dll. System.Data.SqlXml.dll just invokes the actual XQuery processor which resides in System.Xml.dll using reflection. XQuery implementation will be done in these steps: *** Relax NG and DSDL in Mono 1.2 Currently we support only RELAX NG as one part of ISO DSDL effort. There is existing Schematron implementation (NMatrix Project: http://sourceforge.net/projects/dotnetopensrc/). With a few changes, it can be used with mono. We also don't have multi-language based validation, namely Namespace-based Validation Dispatch Language (NVDL). To support unwrapping, one special XmlReader implementation is required (other schema validation support will be done by ReadSubtree()). Note that we had seen RELAX Namespace, Modular Namespace (MNS) and Namespace Routing Language (NRL) - that is, standardization effort is still ongoing (though NVDL looks mostly the same as NRL). In Mono 1.2, there might be improvements on Commons.Xml.Relaxng. ** Tools *** xsd.exe See ADO.NET page. Microsoft has another inference class from XmlReader to XmlSchemaCollection (Microsoft.XsdInference). It may be useful, but it won't be so easy. ** Miscellaneous *** Mutual assembly dependency Sometimes I hear complain about System.dll and System.Xml.dll mutual dependency: System.dll references to System.Xml.dll (e.g. System.Configuration.ConfigXmlDocument extended from XmlDocument), while System.Xml.dll vice versa (e.g. XmlUrlResolver.ResolveUri takes System.Uri). Since they are in public method signatures, so at least we cannot get rid of these mutual references. Nowadays System.Xml.dll is built using incomplete System.dll (lacking System.Xml dependent classes such as ConfigXmlDocument). Full System.dll is built after System.Xml.dll is done. Note that you still need System.dll to run mcs. Atsushi Eno last updated 08/03/2004