What does elementFormDefault do in XSD

Question

What does elementFormDefault do  and when should it be used   So I found some definitions for elementFormDefault values      qualified - elements and attributes   are in the targetNamespace of the   schema       unqualified - elements and   attributes do not have a namespace   So from that definition I would think that if a schema is set to qualified then why must you prefix the type with the namespace   And what are the scenarios that you would even have one set to unqualified for that matter   I tried Googling  but all I got were a couple W3C pages that were extremely hard to understand   This is the file I am working with right now  why do I need to declare the type as target TypeAssignments when I declare the targetNamespace as the same one as xmlns target    lt  xml version  1 0  encoding  UTF-8   gt   lt schema xmlns  http   www w3 org 2001 XMLSchema          xmlns target  http   www levijackson net web340 ns          targetNamespace  http   www levijackson net web340 ns           elementFormDefault  qualified  gt     lt element name  assignments  gt       lt complexType gt         lt sequence gt           lt element name  assignments  type  target TypeAssignments                   minOccurs  1  maxOccurs  unbounded   gt         lt  sequence gt       lt  complexType gt     lt  element gt     lt complexType name  TypeAssignments  gt       lt sequence gt         lt element name  assignment  type  target assignmentInfo                 minOccurs  0  maxOccurs  unbounded   gt       lt  sequence gt     lt  complexType gt     lt complexType name  assignmentInfo  gt       lt sequence gt         lt element name  name  type  string   gt         lt element name  page  type  target TypePage   gt         lt element name  file  type  target TypeFile                  minOccurs  0  maxOccurs  unbounded   gt       lt  sequence gt       lt attribute name  id  type  string  use  required   gt     lt  complexType gt     lt simpleType name  TypePage  gt       lt restriction base  integer  gt         lt minInclusive value  50    gt         lt maxInclusive value  498    gt       lt  restriction gt     lt  simpleType gt     lt simpleType name  TypeFile  gt       lt restriction base  string  gt         lt enumeration value   xml    gt         lt enumeration value   dtd    gt         lt enumeration value   xsd    gt       lt  restriction gt     lt  simpleType gt   lt  schema gt

User · Accepted Answer

ElementFormDefault has nothing to do with namespace of the types in the schema, it's about the namespaces of the elements in XML documents which comply with the schema.

Here's the relevent section of the spec:

Element Declaration Schema

Component Property  {target namespace}
Representation      If form is present and its ·actual value· is qualified, 
                    or if form is absent and the ·actual value· of 
                    elementFormDefault on the <schema> ancestor is qualified, 
                    then the ·actual value· of the targetNamespace [attribute]
                    of the parent <schema> element information item, or 
                    ·absent· if there is none, otherwise ·absent·.

What that means is that the targetNamespace you've declared at the top of the schema only applies to elements in the schema compliant XML document if either elementFormDefault is "qualified" or the element is declared explicitly in the schema as having form="qualified".

For example: If elementFormDefault is unqualified -

<element name="name" type="string" form="qualified"></element>
<element name="page" type="target:TypePage"></element>

will expect "name" elements to be in the targetNamespace and "page" elements to be in the null namespace.

To save you having to put form="qualified" on every element declaration, stating elementFormDefault="qualified" means that the targetNamespace applies to each element unless overridden by putting form="unqualified" on the element declaration.

User · Answer

elementFormDefault  qualified  is used to control the usage of namespaces in XML instance documents   xml file   rather than namespaces in the schema document itself   xsd file    By specifying elementFormDefault  qualified  we enforce namespace declaration to be used in documents validated with this schema   It is common practice to specify this value to declare that the elements should be qualified rather than unqualified  However  since attributeFormDefault  unqualified  is the default value  it doesn t need to be specified in the schema document  if one does not want to qualify the namespaces

User · Answer

Important to note with elementFormDefault is that it applies to locally defined elements  typically named elements inside a complexType block  as opposed to global elements defined on the top-level of the schema  With elementFormDefault  qualified  you can address local elements in the schema from within the xml document using the schema s target namespace as the document s default namespace   In practice  use elementFormDefault  qualified  to be able to declare elements in nested blocks  otherwise you ll have to declare all elements on the top level and refer to them in the schema in nested elements using the ref attribute  resulting in a much less compact schema   This bit in the XML Schema Primer talks about it  http   www w3 org TR xmlschema-0  NS

User · Answer

Consider the following ComplexType AuthorType used by author element   lt xsd complexType name  AuthorType  gt     lt  -- compositor goes here -- gt     lt xsd sequence gt        lt xsd element name  name  type  xsd string   gt        lt xsd element name  phone  type  tns Phone   gt     lt  xsd sequence gt     lt xsd attribute name  id  type  tns AuthorId   gt   lt  xsd complexType gt   lt xsd element name  author  type  tns AuthorType   gt    If elementFormDefault  unqualified   then following XML Instance is valid   lt x author xmlns x  http   example org publishing  gt      lt name gt Aaron Skonnard lt  name gt      lt phone gt  801 390-4552 lt  phone gt   lt  x author gt    the authors s name attribute is allowed without specifying the namespace unqualified   Any elements which are a part of  lt xsd complexType gt  are considered as local to complexType   if elementFormDefault  qualified   then the instance should have the local elements qualified   lt x author xmlns x  http   example org publishing  gt      lt x name gt Aaron Skonnard lt  name gt      lt x phone gt  801 390-4552 lt  phone gt   lt  x author gt    please refer this link for more details

User · Answer

I have noticed that XMLSpy at least 2011 version needs a targetNameSpace defined if elementFormDefault  qualified   is used  Otherwise won t validate  And also won t generate xmls with namespace prefixes

User · Answer

New  detailed answer and explanation to an old  frequently asked question    Short answer  If you don t add elementFormDefault  quot qualified quot  to xsd schema  then the default unqualified value means that locally declared elements are in no namespace  There s a lot of confusion regarding what elementFormDefault does  but this can be quickly clarified with a short example    Streamlined version of your XSD   lt  xml version  quot 1 0 quot  encoding  quot UTF-8 quot   gt   lt schema xmlns  quot http   www w3 org 2001 XMLSchema quot          xmlns target  quot http   www levijackson net web340 ns quot          targetNamespace  quot http   www levijackson net web340 ns quot  gt     lt element name  quot assignments quot  gt       lt complexType gt         lt sequence gt           lt element name  quot assignment quot  type  quot target assignmentInfo quot                    minOccurs  quot 1 quot  maxOccurs  quot unbounded quot   gt         lt  sequence gt       lt  complexType gt     lt  element gt     lt complexType name  quot assignmentInfo quot  gt       lt sequence gt         lt element name  quot name quot  type  quot string quot   gt       lt  sequence gt       lt attribute name  quot id quot  type  quot string quot  use  quot required quot   gt     lt  complexType gt   lt  schema gt   Key points   The assignment element is locally defined  Elements locally defined in XSD are in no namespace by default   This is because the default value for elementFormDefault is unqualified  This arguably is a design mistake by the creators of XSD  Standard practice is to always use elementFormDefault  quot qualified quot  so that assignment is in the target namespace as one would expect    It is a rarely used form attribute on xs element declarations for which elementFormDefault establishes default values   Seemingly Valid XML This XML looks like it should be valid according to the above XSD   lt assignments xmlns  quot http   www levijackson net web340 ns quot               xmlns xsi  quot http   www w3 org 2001 XMLSchema-instance quot               xsi schemaLocation  quot http   www levijackson net web340 ns try xsd quot  gt     lt assignment id  quot a1 quot  gt       lt name gt John lt  name gt     lt  assignment gt   lt  assignments gt   Notice   The default namespace on assignments places assignments and all of its descendents in the default namespace  http   www levijackson net web340 ns    Perplexing Validation Error Despite looking valid  the above XML yields the following confusing validation error    Error  try xml 4 23  cvc-complex-type 2 4 a  Invalid content was found starting with element  assignment   One of   assignment   is expected   Notes   You would not be the first developer to curse this diagnostic that seems to say that the content is invalid because it expected to find an assignment element but it actually found an assignment element    WTF  What this really means  The   and   around assignment means that validation was expecting assignment in no namespace here   Unfortunately  when it says that it found an assignment element  it doesn t mention that it found it in a default namespace which differs from no namespace   Solution  Vast majority of the time  Add elementFormDefault  quot qualified quot  to the xsd schema element of the XSD   This means valid XML must place elements in the target namespace when locally declared in the XSD  otherwise  valid XML must place locally declared elements in no namespace  Tiny minority of the time  Change the XML to comply with the XSD s requirement that assignment be in no namespace   This can be achieved  for example  by adding xmlns  quot  quot  to the assignment element    Credits  Thanks to Michael Kay for helpful feedback on this answer

[xml] What does elementFormDefault do in XSD?

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