I am doing some xsd cleanup activity with limited knowledge on XSD. The file I have contains a complex element with two attribute defined, but differently.
<xs:attribute name="DecisioningRequestType"
type="xs:string"
use="required"/>
<xs:attribute name="ProcessingRequestType"
use="required">
<xs:simpleType>
<xs:restriction base="xs:string"/>
</xs:simpleType>
</xs:attribute>
Through when xml is created, both attribute contain a string value, but I am trying to understand what difference does it make when the attribute are defined with restriction? Isn't that I can define my second attribute similar to the first attribute shown above?
If it is same, I can bring a uniformity in defining the attributes in my XSD file through this cleanup.
Attribute with restriction means that the type of the attribute value is defined
inline, directly within the definition of the attribute itself.
That is used when, on one hand, the attribute type is something special (not just a base type) but, on other hand, it is used only for that attribute.
So, defining that type as a separate component would be redundant.
But in your case, the construct:
<xs:attribute name="ProcessingRequestType" use="required">
<xs:simpleType>
<xs:restriction base="xs:string"/>
</xs:simpleType>
</xs:attribute>
although is valid, actually doesn't restrict anything (it is an empty restriction).
So, it is equivalent to
<xs:attribute name="ProcessingRequestType" type="xs:string" use="required"/>
A true restriction would look something like this:
<xs:attribute name="ProcessingRequestType" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="typeA"/>
<xs:enumeration value="typeB"/>
<xs:enumeration value="typeC"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
That means that the attribute value is a string, however restricted to be only one from the list: "typeA", "typeB", "typeC".
The declaration of an attribute requires that the type of the attribute be specified; this can be done either with a type attribute giving the name of the type, or with an inline declaration of an anonymous type.
The use or non-use of the XSD restriction element is orthogonal to the difference between a type attribute and a simpleType child. In the case you give, the restriction is vacuous; the inline declaration could just as easily have taken the form
<xs:simpleType>
<xs:union memberTypes="xs:string"/>
</xs:simpleType>
You write both attribute contain a string value -- this is true enough, as far as it goes, but the two attributes do not have the same type: one is associated with type xs:string and the other with an anonymous type whose value and lexical spaces are the same as those of xs:string (because it was created by a vacuous restriction of xs:string). In some cases, that difference can be important.
Related
I store settings of my script in XML document. The script is multiplatform but some of its settings are not. I created proper attribute in my XSD file. It decides to which system is the setting.
<xs:attribute name="system" use="optional" default="none">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="none"/>
<xs:enumeration value="windows"/>
<xs:enumeration value="unix"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
A sample XML file looks like below. (Don't read too carefully. It's just an example.)
<root>
<name>Foo</name>
<path system="windows">%appdata%\Bar</path>
<path system="unix">~/Bar/</path>
<foo system="unix">
<bar>baz</bar>
<!-- more elements -->
</foo>
<foo>
<bar system="windows">baz</bar>
<!-- more elements -->
</foo>
</root>
The problem is I need possibility to add attribute system to each element of my XML. At this moment I can't simply write:
<xs:element name="path" type="xs:string"/>
Instead that I have to write:
<xs:element name="path">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute ref="system"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
(I know that I can define complex type before and use it multiple times.) It is very expanded XSD and I have a lot of my own types in it. Many of them are used in one place only. Actually I set attribute system to each type in my XSD but it takes a lot of space and is not very readable.
Is it possible to set attribute to all types in XSD?
Your options for globally defining a common attribute to be used in many locations include:
Have all types derive from a common type that includes the attribute.
Use xs:attribute/#ref, which you've already mentioned.
Use xs:attributeGroup/#ref, which would allow you to reference multiple
commonly declared attributes collectively. Update: In XSD 1.1, a default attribute
group can be specified via defaultAttributes on the xs:schema element that applies to all
complex type definitions. Thanks to #sergioFC for this good idea.
Use xs:any element, and then (in XSD 1.1) xs:assert about the attribute, but
then you lose most of the normal element and attribute declaration
facilities due to xs:any's intrinsic leniency.
Other than such indirect options, there is no mechanism in XSD for centrally stating that an attribute may/must be present on all elements.
I have following schema
<xs:simpleType name="enumType">
<xs:restriction base="xs:string">
<xs:enumeration value="STRING_ONE"/>
<xs:enumeration value="STRING_TWO"/>
</xs:restriction>
</xs:simpleType>
As long as i get a known string, I can swithc and it to my jaxbobject which expects a enumType object. But what if i don't know this string ? is there a way to handle it based on JAXB Schema ? I know based on enum its not possible.
Edit: Trying to make it more clear
Wit the given Schema design, my JAXBObject, which accepts enumType as a parameter, can only have 2 input values i.e. STRING_ONE or STRING_TWO which will be converted to XML as part of marshalling.
The question is, that what if, I want to handle a situation through my schema design that if I can have an object of enumType then good otherwise I can give an XML to JAXBObject instead of enumType and it still parses it.
From the XSD point of view, it sounds like you want to be able to write
<xs:simpleType name="soft-enumeration">
<xs:union>
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="STRING_ONE"/>
<xs:enumeration value="STRING_TWO"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType>
<xs:union memberTypes="xs:string"/>
</xs:simpleType>
</xs:union>
</xs:simpleType>
This type includes the enumeration you describe, but it then unions it with xs:string, so as to accept other values as well. If your schema interface gives you access to information about which member type of the union was used, then you can use that information to treat instances of STRING_ONE and STRING_TWO differently from other strings.
I have no idea whether jaxb does anything useful with this idiom, however; there you're on your own.
I'm trying to define an element type in XSD, for which i want an optional attribute, which if present can either contain a float, or be empty (but still present).
i.e:
<xs:element name="MyElement">
<xs:complexType>
<xs:attribute name="optionalFloatAttribute" type="xs:float" use="optional"/>
</xs:complexType>
</xs:element>
Needs "fixing" to allow all of the following xml:-
<MyElement/>
or
<MyElement optionalFloatAttribute=""/>
or
<MyElement optionalFloatAttribute="3.14159"/>
The only way I can see of doing this is to change type to xs:string, and use xs:restriction with a regular expression. But this doesn't seem very ideal to me. Is there a better way?
And I have to be able to support these variations of the xml - the program and existing xml is legacy, and I am trying to back-create a schema to match the myriad variations I see in what we have to regard as valid xml.
You can define custom type for that by combining float and empty string:
<xs:element name="MyElement">
<xs:complexType>
<xs:attribute name="optionalFloatAttribute" type="emptyFloat" use="optional"/>
</xs:complexType>
</xs:element>
<xs:simpleType name="emptyFloat">
<xs:union>
<xs:simpleType>
<xs:restriction base='xs:string'>
<xs:length value="0"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType>
<xs:restriction base='xs:float'>
</xs:restriction>
</xs:simpleType>
</xs:union>
</xs:simpleType>
Or using regExp:
<xs:simpleType name="emptyFloat">
<xs:restriction base="xs:string">
<xs:pattern value="-?\d*\.?\d*"/>
</xs:restriction>
</xs:simpleType>
If you could stand using an element rather than an attribute you could make the xs:float nillable. This way you can use the xsi:nil="true" in your instance document to indicate that the element has no value:
<!-- definition -->
<xs:element name="quantity" type="xs:float" nillable="true" />
<!-- instance -->
<quantity xsi:nil="true" />
No equivalent for attributes though.
I don't think there's a way to handle this and use xs:float. Fundamentally it comes down to the fact that empty string isn't a valid number. You'd either normally expect a value of 0, or for the element to be missing altogether. There's a good explanation as the answer to the following question:
Empty elements for primitve datatypes forbidden in XSD
It seems that the option of using xs:string and a regexp might be your best plan.
Is there a way to define a constant value and use that constant in the preceeding XSD? I have a common value I want to use for various xs:element tag's maxOccurs attributes. Like constants in other languages, I want to make the change in one place should the value backing MyConst were to ever change.
<!-- Can I do this? -->
<ConstantValue id="MyConst" value="10"/>
...
<xs:element name="sandwich_meat" type="xs:string" minOccurs="0" maxOccurs="MyConst"/>
<xs:element name="sandwich_name" type="xs:string" minOccurs="0" maxOccurs="MyConst"/>
You can try to define a simpleType with a restriction:
<xs:simpleType name="AConstantHere">
<xs:restriction base="xs:string">
<xs:enumeration value="CONSTANT_VALUE_HERE"/>
</xs:restriction>
</xs:simpleType>
It allows only one value.
No it is not allowed that way. However you can define your own type with a fixed value in it somewhere on top of your XSD (place dosen matters) and use that type for the elements.
It's not possible with plain schema, but maybe XML entities will do the trick?
I have seen XML Schema element with attributes containing only text but I have an element that's an xs:dateTime instead.
The document I'm trying to write a schema for looks like this:
<web-campaigns>
<web-campaign>
<id>1231</id>
<start-at nil="true"/>
</web-campaign>
<web-campaign>
<id>1232</id>
<start-at>2009-08-08T09:00:00Z</start-at>
</web-campaign>
</web-campaigns>
Sometimes the xs:dateTime element has content, sometimes it doesn't.
What I have so far (which doesn't validate yet) is:
<xs:element name="start-at">
<xs:complexType mixed="true">
<xs:simpleContent>
<xs:extension base="xs:dateTime">
<xs:attribute name="nil" default="false" type="xs:boolean" use="optional" />
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
If I replace xs:dateTime with xs:string, I can validate the document just fine, but I really want an xs:dateTime, to indicate to consumers what's in that element. I tried with/without mixed="true" as well, to no avail.
If it makes a difference, I validate using xmllint (on Mac OS X 10.5) and XML Schema Validator
you can define your own types as union of types.
1/ define the "empty" type as a string that only allows "" ähm nothing :)
<xs:simpleType name="empty">
<xs:restriction base="xs:string">
<xs:enumeration value=""/>
</xs:restriction>
</xs:simpleType>
2/ next define a type that allows date AND empty
<xs:simpleType name="empty-dateTime">
<xs:union memberTypes="xs:dateTime empty"/>
</xs:simpleType>
3/ declare all your nullable datetime elements as type="empty-dateTime"
You need
<xs:element name="start-at" minOccurs="0">
mixed-mode isn't relevant to your situation, you don't need that. By default, minOccurs="1", i.e. the element is mandatory.
With minOccurs="0", you either specify the element with content, or not at all. If you want to be able to permit <start-at/>, then you cannot use xs:dateTime.