How should I reference another complexType in xml, as element or as attribute over my own defined Key? What is the correct approach to model the following self-reference? Is the first approach even possible, or does it lead to infinite self-referencing?
<xs:complexType name="Category">
<xs:sequence>
<xs:element name="ParentCategory" type="Category" minOccurs="1" maxOccurs="1"></xs:element>
<xs:element name="ChildCategory" type="Category" minOccurs="0" maxOccurs="unbounded"></xs:element>
</xs:sequence>
<xs:attribute name="CategoryName" type="xs:string"></xs:attribute>
</xs:complexType>
or
<xs:complexType name="Category">
<xs:sequence>
<xs:element name="ChildCategory" type="Category" minOccurs="0" maxOccurs="unbounded"></xs:element>
</xs:sequence>
<xs:attribute name="CategoryName" type="xs:string"></xs:attribute>
<xs:attribute name="ParentCategory" type="xs:string"></xs:attribute>
</xs:complexType>
I'm a bit confused - since I want to be object oriented, but am not sure how this would look like in XML. Wouldn't the reference of ParentCategory as a Category-type require me to again write a Category-type in XML that itself has a ParentCategory child-element, etc... leading to infinite type-referencing.
There's no issue referencing an element of the same type as part of the type definition, so your first example is fine from that point of view. Trying to reference the parent is a bit odd though, you shouldn't really need to do this... XML is hierarchical after all.
<xs:complexType name="Category">
<xs:sequence>
<xs:element maxOccurs="unbounded" minOccurs="0" name="ChildCategory" type="Category"/>
</xs:sequence>
<xs:attribute name="CategoryName" type="xs:string"/>
</xs:complexType>
The Category type references itself recursively, allowing for 0 or more ChildCategory elements. This should do what you need (there's nothing wrong with recursive type referencing in the XML Schema).
If you need to refer to the parent Category in your document, it's easy enough to chain to the parent node in any DOM implementation or with XPath.
Related
I have the following XSD structure:
<xs:schema xmlns:ns="http://abc/">
...
<xs:element name="abc">
<xs:complexType>
<xs:sequence>
<xs:element ref="map"/>
</xs:sequence>
</xs:complexType>
</xs:element>
...
<xs:element name="map">
<xs:complexType>
<xs:sequence>
<xs:element name="entry" type="ns:MapEntryType" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:unique name="entry">
<xs:selector xpath="entry"/>
<xs:field xpath="key"/>
</xs:unique>
</xs:element>
<xs:complexType name="MapEntryType">
<xs:sequence>
<xs:element name="key" type="xs:string"/>
<xs:element name="value" type="xs:anyType"/>
</xs:sequence>
</xs:complexType>
</xs:schema>
This is doing its job.
The map element now has to be called something different based on whichever is the wrapper, so the name is sometimes map, sometimes properties, sometimes options, etc.
Therefore I want to genericize the map element.
I tried doing the following:
Making map a xs:complexType and changing ref to type.
This resulted in xs:unique not being accepted and failed
Making map a xs:complexType, changing ref to type and moving the xs:unique constraint to the element definitions.
This worked but resulted in the XSD having a lot of xs:unique present in the document.
Isn't there a way to simply tell that I want a specific structure and it containing unique elements without having to repeat the unique constraint everywhere?
As Petru Gardea said in his answer
Both XSD 1.0 and 1.1 place the identity constraints under an element
So you have to add xs:unique to every element, but if you are using XSD 1.1 you can define only once a complete xs:unique and then in the rest of the elements use xs:unique ref="name". This is not valid for you as you are using XSD 1.0, but I let it here for future XSD 1.1 users that find this good question.
Example (namespaces removed for clarity):
<xs:element name="map">
<xs:complexType>
<xs:sequence>
<xs:element name="entry" type="MapEntryType" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<!-- Only completely defined once -->
<xs:unique name="uniqueEntry">
<xs:selector xpath="entry"/>
<xs:field xpath="key"/>
</xs:unique>
</xs:element>
<xs:element name="hashMap">
<xs:complexType>
<xs:sequence>
<xs:element name="entry" type="MapEntryType" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<!-- Referenced here and every other time -->
<xs:unique ref="uniqueEntry"/>
</xs:element>
Short answer, it is not possible. Both XSD 1.0 and 1.1 place the identity constraints under an element; a constraint cannot be globally defined, therefore there is no "reuse" per se, other than that of the enclosing element. Given your scenario (different element names for different needs) it is not possible to reuse.
I'm trying to define a schema for some xml-based database exchange like this:
<table name="foo">
<row>
<fooid>15</fooid>
<fooname>some entry</fooname>
</row>
<row>
<fooid>28</fooid>
<fooname>something else</fooname>
</row>
</table>
<table name="bar">
<row>
<barid>19</barid>
<barcounter>93</barcounter>
</row>
</table>
so I have several of these tables and within these tables there should be only the fields that exist in these tables. For example barid should not appear in table foo.
Is there any way to define this?
Yes, there are two ways. One is simple (and relies on some human intuition and documentation), and the other is more expressive (but inevitably also a bit more complicated.)
The simple way is to replace the names 'table' and 'row' with names that indicate what table we are talking about:
<table-foo>
<row-foo>
<fooid>28</fooid>
<fooname>something</fooname>
</row-foo>
...
</table-foo>
<table-bar>
<row-bar>
<barid>19</barid>
<barcounter>93</barcounter>
</row-bar>
...
</table-bar>
XSD validation (like validation using DTDs and Relax NG) is based principally on the element names used. If you want two different kinds of row to contain different things, give them two different names. So foo-table and its descendants can be declared thus:
<xs:element name="table-foo" substitutionGroup="tns:table">
<xs:complexType>
<xs:sequence>
<xs:element ref="tns:row-foo"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="row-foo" substitutionGroup="tns:row">
<xs:complexType>
<xs:sequence>
<xs:element ref="tns:fooid"/>
<xs:element ref="tns:fooname"/>
</xs:sequence>
</xs:complexType>
And similarly for bar-table and bar-row.
Sometimes, however, we absolutely must, or really want to, capture the fact that both 'row-foo' and 'row-bar' have something crucial in common. They are both 'rows' in some abstract ontology, and that may matter to us. In such cases, you can use abstract elements to capture the regularity.
For example, here is a simple abstraction for tables, rows, and cells:
<xs:element name="table"
abstract="true"
type="tns:table"/>
<xs:element name="row"
abstract="true"
type="tns:row"/>
<xs:element name="cell"
abstract="true"
type="xs:anySimpleType"/>
The types for table and row are straightforward:
<xs:complexType name="table">
<xs:sequence>
<xs:element ref="tns:row" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="row">
<xs:sequence>
<xs:element ref="tns:cell" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
Now, the declarations for table-foo etc. become slightly more complicated, because for each declaration we have to establish a relation to the abstraction we have just defined. Element foo-table is an instantiation of the table abstraction, and its type is a restriction of the abstract table type:
<xs:element name="table-foo"
substitutionGroup="tns:table">
<xs:complexType>
<xs:complexContent>
<xs:restriction base="tns:table">
<xs:sequence>
<xs:element ref="tns:row-foo"/>
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
</xs:element>
Element foo-row is similar: we specify that it's a "row" by using the substitutionGroup attribute, and we derive its complex type by restriction from the abstract row type:
<xs:element name="row-foo" substitutionGroup="tns:row">
<xs:complexType>
<xs:complexContent>
<xs:restriction base="tns:row">
<xs:sequence>
<xs:element ref="tns:fooid"/>
<xs:element ref="tns:fooname"/>
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
</xs:element>
Note that we don't allow arbitrary cells to appear here, just the two cell types we want for rows from table foo. And to close off the pattern, we declare that the elements fooid and fooname are cells, using (again) substitutionGroup.
<xs:element name="fooid" type="xs:integer"
substitutionGroup="tns:cell"/>
<xs:element name="fooname" type="xs:string"
substitutionGroup="tns:cell"/>
The same patterns can be used to declare a different set of legal cells for table bar:
<xs:element name="barid" type="xs:positiveInteger"
substitutionGroup="tns:cell"/>
<xs:element name="barcounter" type="xs:double"
substitutionGroup="tns:cell"/>
<xs:element name="table-bar" substitutionGroup="tns:table">
<xs:complexType>
<xs:complexContent>
<xs:restriction base="tns:table">
<xs:sequence>
<xs:element ref="tns:row-bar"/>
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:element name="row-bar" substitutionGroup="tns:row">
<xs:complexType>
<xs:complexContent>
<xs:restriction base="tns:row">
<xs:sequence>
<xs:element ref="tns:barid"/>
<xs:element ref="tns:barcounter"/>
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
</xs:element>
The situation you describe is one of the use cases for which abstract elements and substitution groups were designed. Other techniques which could also be used here (but which I won't illustrate in detail) include:
Declared subtypes, use of xsi:type (declare foo-table and bar-table as restrictions or extensions of type table, use <table xsi:type="tns:foo-table">...</table> or <table xsi:type="tns:bar-table">...</table> to guide validation)
Assertions (declare foo-table and bar-table types which extend the generic table type by adding assertions about the grandchildren -- this is an XSD 1.1 feature not available in 1.0).
Conditional type assignment (declare that table gets one type if it has name="foo" and a different type if it has name="bar" -- also an XSD 1.1 feature not available in 1.0).
There may be other ways to do it, too.
I am creating an XSD where I defined a complex type:
<xs:complexType name="TimeBasicComponents">
<xs:sequence>
<xs:element name="Hours" type="xs:int"></xs:element>
<xs:element name="Minutes" type="xs:int"></xs:element>
<xs:element name="Seconds" type="xs:int"></xs:element>
<xs:element name="MilliSeconds" type="xs:int"></xs:element>
</xs:sequence>
</xs:complexType>
I defined another complex type:
<xs:complexType name="TimeOfDay">
<xs:sequence>
<xs:element name="BasicComponents" type="TimeBasicComponents"></xs:element>
<xs:element name="Zone" type="xs:string"></xs:element>
</xs:sequence>
</xs:complexType>
Now, I want to have another complex type for time duration. However, there is actually no need to define another complex type for this, it will be exactly same as "TimeBasicComponents". So, I was wondering if there is way to define multiple names for a single complex type in XSD?
-Sandeep
Are you saying that you want to use TimeBasicComponents as a duration also? To my knowledge you can't have alias'es for a complexType but you can achieve something very similar using the <xs:extension... construct:
<xs:complexType name="TimeDuration">
<xs:complexContent>
<xs:extension base="TimeBasicComponents" />
</xs:complexContent>
</xs:complexType>
That way you will effectively have an alias without having to redefine the TimeBasicComponents complex-type.
Cheers,
I've a base class, marked as abstract:
<!-- TYPE: BASE CLASS -->
<xs:complexType name="BaseClass" abstract="true">
<xs:sequence>
<xs:element name="name" type="xs:string" minOccurs="1" maxOccurs="1"/>
<xs:element name="implementation" type="BaseClass" minOccurs="0" maxOccurs="1"/>
</xs:sequence>
</xs:complexType>
Now the class that inherits BaseClass and overrides 'implementation' with null:
<xs:complexType name="MyClass">
<xs:complexContent>
<xs:extension base="BaseClass"/>
</xs:complexContent>
</xs:complexType>
I've tried this but is invalid:
<xs:complexType name="MyClass">
<xs:complexContent>
<xs:extension base="BaseClass">
<xs:sequence>
<xs:element name="implementation" fixed="xs:nil"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
Is there a way to do this?
Marking something as abstract in XSD schema basically means that it cannot appear in an instance document. It should be used with the substitutionGroup attribute.
For example
<xs:element name="replaceme" abstract="true" />
<xs:element name="replacement1" substitutionGroup="replaceme" />
<xs:element name="replacement2" substitutionGroup="replaceme" />
This means that in an instance document you would be forced to use either a "replacement1" or a "replacement2" element, ie the xsd is forcing you to substitute the "replaceme" element with one of the replacements from the substitution group.
So to achieve what you want you need to create a substitution group consisting of the types you want to use instead of your base type. I am not sure this is possible with complex types but give it a go.
This is a part of my xml schema
<xs:complexType name="Friend">
<xs:all>
<xs:element name="name" type="xs:string" />
<xs:element name="phone" type="xs:string" />
<xs:element name="address" type="xs:string" />
</xs:all>
</xs:complexType>
<xs:complexType name="Coworker">
<xs:all>
<xs:element name="name" type="xs:string" />
<xs:element name="phone" type="xs:string" />
<xs:element name="office" type="xs:string" />
</xs:all>
</xs:complexType>
For better maintainability, I would like to have the shared attributes in an (abstract) super type or something like that. But more important, I want that all elements are unordered and also optional.
Is this possible, and what is the best way to do it?
You have to limit yourself a little bit, some of the things you are trying to do are not possible in XML Schema.
Suppose you introduce a complex type called Person to be a super-type of Friend and Coworker. Here are your options:
Replace xs:all with xs:sequence, remove name and phone from the sub-types, add to the super-type, and add inheritance. Your elements now have to be ordered, but you can make them individually optional. It is illegal to use xs:all in type hierarchies in XML Schema, because the processor cannot tell where the parent content model stops and the child content model starts.
Replace xs:all with <xs:choice maxOccurs="unbounded"> in both types, and add your inheritance. Then your elements become unordered again, but they may repeat.
So in conclusion: given your type names up there, I would guess that your requirements will not be exactly met. I would go for the first option: insisting on arbitrary element order is often not as useful as it seems.
One-and-half year after this question and the accepted answer were posted, XSD 1.1 was published. In this version it is possible to specify what the OP asked for because a number of restriction on xs:all were lifted. One of them is that it is now possible to extend an xs:all.
Using XSD 1.1 you can specify the following:
<xs:complexType name="Person" abstract="true">
<xs:all>
<xs:element name="name" type="xs:string" minOccurs="0" />
<xs:element name="phone" type="xs:string" minOccurs="0" />
</xs:all>
</xs:complexType>
<xs:complexType name="Friend">
<xs:complexContent>
<xs:extension base="Person">
<xs:all>
<xs:element name="address" type="xs:string" minOccurs="0" />
</xs:all>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="Coworker">
<xs:complexContent>
<xs:extension base="Person">
<xs:all>
<xs:element name="office" type="xs:string" minOccurs="0" />
</xs:all>
</xs:extension>
</xs:complexContent>
</xs:complexType>
This defines the following types:
Person: an abstract type with optional unordered name and phone elements;
Friend: extends Person adding an optional address element to the list of unordered elements;
Coworker: extends Coworker adding an optional office element to the list of unordered elements.
Note that this solution does not work for every XML processor: even though 8 years have passed since the publication of XSD 1.1, a lot of processors still only support XSD 1.0.