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.NET Forum / .NET Framework / XML / November 2004substitutionGroup and extension problem
Hi, I'm working on an xml schema and I'm running into some problems relating substitutionGroups and extensions. This xsd validates fine: There are three elements and three complex types and every element has the type of some complexType. <?xml version="1.0" encoding="UTF-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified"> <xs:element name="Catalogue"> <xs:complexType> <xs:sequence> <xs:element ref="Publication" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="Publication" type="PublicationType" abstract="true"/> <xs:element name="Book" type="BookType" substitutionGroup="Publication"/> <xs:element name="Magazine" type="MagazineType" substitutionGroup="Publication"/> <xs:complexType name="PublicationType"> <xs:sequence> <xs:element name="Title" type="xs:string"/> <xs:element name="Author" type="xs:string" minOccurs="0" maxOccurs="unbounded"/> <xs:element name="Date" type="xs:gYear"/> </xs:sequence> </xs:complexType> <xs:complexType name="BookType"> <xs:complexContent> <xs:extension base="PublicationType"> <xs:sequence> <xs:element name="ISBN" type="xs:string"/> <xs:element name="Publisher" type="xs:string"/> </xs:sequence> </xs:extension> </xs:complexContent> </xs:complexType> <xs:complexType name="MagazineType"> <xs:complexContent> <xs:restriction base="PublicationType"> <xs:sequence> <xs:element name="Title" type="xs:string"/> <xs:element name="Author" type="xs:string" minOccurs="0" maxOccurs="0"/> <xs:element name="Date" type="xs:gYear"/> </xs:sequence> </xs:restriction> </xs:complexContent> </xs:complexType> </xs:schema> Now, if I change the schema so that the elements extend the complex type, so instead of <xs:element name="Book" type="BookType" substitutionGroup="Publication"/> I say: <xs:element name="Book" substitutionGroup="Publication"> <xs:complexType> <xs:complexContent> <xs:extension base="BookType"> </xs:extension> </xs:complexContent> </xs:complexType> </xs:element> The schema now looks like this: <?xml version="1.0" encoding="UTF-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified"> <xs:element name="Catalogue"> <xs:complexType> <xs:sequence> <xs:element ref="Publication" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="Publication" abstract="true"> <xs:complexType> <xs:complexContent> <xs:extension base="PublicationType"> </xs:extension> </xs:complexContent> </xs:complexType> </xs:element> <xs:element name="Book" substitutionGroup="Publication"> <xs:complexType> <xs:complexContent> <xs:extension base="BookType"> </xs:extension> </xs:complexContent> </xs:complexType> </xs:element> <xs:element name="Magazine" substitutionGroup="Publication"> <xs:complexType> <xs:complexContent> <xs:extension base="MagazineType"> </xs:extension> </xs:complexContent> </xs:complexType> </xs:element> <xs:complexType name="PublicationType"> <xs:sequence> <xs:element name="Title" type="xs:string"/> <xs:element name="Author" type="xs:string" minOccurs="0" maxOccurs="unbounded"/> <xs:element name="Date" type="xs:gYear"/> </xs:sequence> </xs:complexType> <xs:complexType name="BookType"> <xs:complexContent> <xs:extension base="PublicationType"> <xs:sequence> <xs:element name="ISBN" type="xs:string"/> <xs:element name="Publisher" type="xs:string"/> </xs:sequence> </xs:extension> </xs:complexContent> </xs:complexType> <xs:complexType name="MagazineType"> <xs:complexContent> <xs:restriction base="PublicationType"> <xs:sequence> <xs:element name="Title" type="xs:string"/> <xs:element name="Author" type="xs:string" minOccurs="0" maxOccurs="0"/> <xs:element name="Date" type="xs:gYear"/> </xs:sequence> </xs:restriction> </xs:complexContent> </xs:complexType> </xs:schema> Now, I get an error validating. Xmlspy 2005 says this: Type Definition "PublicationType" is directly derived from 'anyType' and, thus, not a valid derivation of 'xs:anyType'. If I try to validate this schema using .net, I get the following errors: Schema parsing error 'Magazine' cannot be a member of substitution group with head element 'Publication'. An error occurred at , (26, 3). Schema parsing error 'Book' cannot be a member of substitution group with head element 'Publication'. An error occurred at , (18, 3). Anybody know what's wrong with this schema? I thought that <xs:element name="Book" type="BookType" substitutionGroup="Publication"/> and: <xs:element name="Book" substitutionGroup="Publication"> <xs:complexType> <xs:complexContent> <xs:extension base="BookType"> </xs:extension> </xs:complexContent> </xs:complexType> </xs:element> are basically the same, because I'm using an extension, but I'm not actually 'extending' it by adding any elements or attributes to it. Thanks in advance, Jeffry Hi Jeffry, They are not the same thing. Using the second syntax, even though you are not adding any elements or attributes, you are still creating a new (anonymous) type that is an extension of BookType. So, when you go to add Book to the Publication substitutionGroup, the type of Book is not derived from the type of Publication; their types are "siblings" in the derivation chain. Just out of curiosity, is there any reason you don't like the first schema you showed us? I think that one's a lot more clear and compact, and allows for further derivation down the line... Hope that helps, Priscilla ------------------------------------------------------------------ Priscilla Walmsley Author, Definitive XML Schema / XML in Office 2003 http://www.datypic.com ------------------------------------------------------------------ > Hi, > [quoted text clipped - 164 lines] > > Jeffry Hi Priscilla, So if I understand correctly. What you're saying is that if I extend BookType in my Book element I create an anonymous type. So would this be basically the same as doing this?: <xs:complexType name="ExtendedBookType"> <xs:complexContent> <xs:extension base="BookType"> </xs:extension> </xs:complexContent> </xs:complexType> <xs:element name="Book" substitutionGroup="Publication"> <xs:complexType> <xs:complexContent> <xs:extension base="ExtendedBookType"> </xs:extension> </xs:complexContent> </xs:complexType> </xs:element> And, the type of Book should derive DIRECTLY from the type of Publication? It is not that if Book derives from ExtendedBookType, ExtendedBookType derives from BookType and BookType derives from PublicationType, that I can substitute the Book element for the Publication element? Anyway, I too like the first schema best. That was what I came up with as a response to the second schema that I received from my customer. We are now discussing the schema's and with your explanation I can argue that the second schema is not correct. Well, I knew it was not correct, because it didn't validate, but now I know why (at least, if my abovementioned understanding of your explanation is correct) :) Thanks a lot, Jeffry > Hi Jeffry, > [quoted text clipped - 186 lines] >> >> Jeffry Hi Jeffry, > What you're saying is that if I extend BookType in my Book element I > create an anonymous type. So would this be basically the same as doing > this?: > <xs:complexType name="ExtendedBookType"> > <xs:complexContent> [quoted text clipped - 11 lines] > </xs:complexType> > </xs:element> No, now the type of Book is an anonymous type that is an extension of ExtendedBookType, which itself is an extension of BookType. That's not the same thing as: <xs:element name="Book" substitutionGroup="Publication"> <xs:complexType> <xs:complexContent> <xs:extension base="BookType"> </xs:extension> </xs:complexContent> </xs:complexType> </xs:element> where the type of Book is an anonymous type that is an extension of BookType (2 types instead of 3). > And, the type of Book should derive DIRECTLY from the type of Publication? > It is not that if Book derives from ExtendedBookType, ExtendedBookType > derives from BookType and BookType derives from PublicationType, that I > can substitute the Book element for the Publication element? It doesn't have to be directly derived from it. But in your 2nd schema the Publication element doesn't have the type PublicationType, it has an anonymous type that is an extension of PublicationType. So what you have is: PublicationType | | anon1 BookType | anon2 where anon1 is the type of Publication and anon2 is the type of Book. anon2 is not considered to be derived from anon1 because it is not a descendent of anon1. Does that make sense? Priscilla ------------------------------------------------------------------ Priscilla Walmsley Author, Definitive XML Schema / XML in Office 2003 http://www.datypic.com ------------------------------------------------------------------ > Hi Priscilla, > [quoted text clipped - 34 lines] > Thanks a lot, > Jeffry Oh stupid me, I meant to say this: <xs:complexType name="ExtendedBookType"> <xs:complexContent> <xs:extension base="BookType"> </xs:extension> </xs:complexContent> </xs:complexType> <xs:element name="Book" type="ExtendedBookType" substitutionGroup="Publication"> </xs:element> But that doesn't make a difference, because of your explanation: PublicationType | | anon1 BookType | anon2 So in the case of what I meant to say, this diagram would look like PublicationType | | anon1 BookType | ExtendedBookType Also in this case the type of Book (ExtendedBookType) doesn't derive from the type of Publication (anon1). I think to point is, which I didn't know and you made perfectly clear, that if an element extends a type, it now has an anonymous type that extends from that type. And that's what causes all the confusion. Right? I hope so :) Thanks you very much for your explanation. Jeffry > Hi Jeffry, > [quoted text clipped - 103 lines] >> Thanks a lot, >> Jeffry Hi Jeffry, > I think to point is, which I didn't know and you made perfectly clear, > that if an element extends a type, it now has an anonymous type that > extends from that type. And that's what causes all the confusion. Right? I > hope so :) Exactly! Priscilla ------------------------------------------------------------------ Priscilla Walmsley Author, Definitive XML Schema / XML in Office 2003 http://www.datypic.com ------------------------------------------------------------------ Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. 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