1. X-Informatics: I-400 and I-590 XML Schema
Spring Semester MW 6:00 pm – 7:15 pm Indiana Time
Geoffrey Fox and Bryan Carpenter
PTLIU Laboratory for Community Grids
Informatics, (Computer Science , Physics)
Indiana University
Bloomington IN 47404
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2. Outline
XML Schema discussion based on
Note that this is reasonably complete – parts 1 and 2 ( etc.) are more formal discussions not extensions in coverage
See (elementary) and note very complete tutorial and examples at
We summarize all the topics in this primer
Basic Schema
Groups
Namespaces
Include
Derived types
Import
Remember: Schema and DTD are like classes in Java
XML files are instances of objects defined in Schema or DTD’s
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3. XML Schema PO Example po.xml I
<?xml version="1.0"?>
<purchaseOrder orderDate=" ">
<shipTo country="US">
<name>Alice Smith</name>
<street>123 Maple Street</street>
<city>Mill Valley</city>
<state>CA</state>
<zip>90952</zip>
</shipTo>
<billTo country="US">
<name>Robert Smith</name>
<street>8 Oak Avenue</street>
<city>Old Town</city>
<state>PA</state>
<zip>95819</zip>
</billTo>
Need to add mechanism to associate schema with this XML
instance
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4. XML Schema PO Example po.xml II
<comment>Hurry, my lawn is going wild!</comment>
<items>
<item partNum="872-AA">
<productName>Lawnmower</productName>
<quantity>1</quantity>
<USPrice>148.95</USPrice>
<comment>Confirm this is electric</comment>
</item>
<item partNum="926-AA">
<productName>Baby Monitor</productName>
<USPrice>39.98</USPrice>
<shipDate> </shipDate>
</items>
</purchaseOrder>
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5. The Purchase Order Schema, po.xsd I
<xsd:schema xmlns:xsd="
<xsd:annotation>
<xsd:documentation>
Purchase order schema for Example.com.
Copyright 2000 Example.com. All rights reserved.
</xsd:documentation>
</xsd:annotation>
<xsd:element name="purchaseOrder" type="PurchaseOrderType"/>
<xsd:element name="comment" type="xsd:string"/>
<xsd:complexType name="PurchaseOrderType">
<xsd:sequence>
<xsd:element name="shipTo" type="USAddress"/>
<xsd:element name="billTo" type="USAddress"/>
<xsd:element ref="comment" minOccurs="0"/>
<xsd:element name="items" type="Items"/>
</xsd:sequence>
<xsd:attribute name="orderDate" type="xsd:date"/>
</xsd:complexType>
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6. The Purchase Order Schema, po.xsd II
<xsd:complexType name="USAddress">
<xsd:sequence>
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="street" type="xsd:string"/>
<xsd:element name="city" type="xsd:string"/>
<xsd:element name="state" type="xsd:string"/>
<xsd:element name="zip" type="xsd:decimal"/>
</xsd:sequence>
<xsd:attribute name="country" type="xsd:NMTOKEN"
use="fixed" value="US"/>
</xsd:complexType>
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7. The Purchase Order Schema, po.xsd III
<xsd:complexType name="Items">
<xsd:sequence>
<xsd:element name="item" minOccurs="0" maxOccurs="unbounded">
<xsd:complexType>
<xsd:element name="productName" type="xsd:string"/>
<xsd:element name="quantity">
<xsd:simpleType>
<xsd:restriction base="xsd:positiveInteger">
<xsd:maxExclusive value="100"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
<xsd:element name="USPrice" type="xsd:decimal"/>
<xsd:element ref="comment" minOccurs="0"/>
<xsd:element name="shipDate" type="xsd:date" minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="partNum" type="SKU"/>
</xsd:complexType>
Anonymous type quantity
Specify item
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8. The Purchase Order Schema, po.xsd IV
</xsd:element> <!– End item specification 
</xsd:sequence> <!– End sequence for items specification 
</xsd:complexType> <!– End items specification 
<!-- Stock Keeping Unit, a code for identifying products -->
<xsd:simpleType name="SKU">
<xsd:restriction base="xsd:string">
<xsd:pattern value="\d{3}-[A-Z]{2}"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:schema>
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9. Comments on po.xsd I
The prefix xsd: is Namespace specified by xmlns:xsd=
The label xsd is conventional; you could use a different one
Schema does two types of things:
Defines new types of elements or attributes e.g. PurchaseOrderType with xsd:complexType or xsd:simpleType
Defines internal elements and attributes for tags e.g. PurchaseOrder using xsd:element and xsd:attribute
So an element like shipTo in po.xml has at most one attribute country which if it appears must have value US. The elements name, street, city, state, zip must appear in this order and the first four are strings; zip is a xsd:decimal
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10. Comments on po.xsd II
The prefix xsd: is Namespace specified by xmlns:xsd=
The label xsd is conventional; you could use a different one
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11. Comments on po.xsd III Schema does two types of things:
Defines new types of elements or attributes e.g. PurchaseOrderType with xsd:complexType
Defines internal elements and attributes for tags e.g. PurchaseOrder using xsd:element and xsd:attribute
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12. Comments on po.xsd IV
So an element like shipTo in po.xml has at most one attribute country which if it appears must have value US. The elements name, street, city, state, zip must appear in this order and the first four are strings; zip is a xsd:decimal
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13. xsd:complexType Example
Anything of PurchaseOrderType is allowed one attribute (orderDate) of type xsd:date.
Further it must consists of 4 elements shipTo, billTo, comment and items in that order
comment can be absent as minOccurs = 0
Note that comment is a global element defined in the schema. It is accessed by ref= rather than type=
One can define global elements or attributes which cannot themselves use ref (global elements are particularly important if one imports this schema into other schema as only global components can be re-used)
minOccurs and maxOccurs have default values of 1 and so shipTo, billTo and items must appear once and once only
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14. Specifying xsd:element and xsd:attribute
Any xsd:element tag can have attribute minOccurs, maxOccurs, fixed and default
Any xsd:attribute can have attribute use and value
Note attributes can NEVER appear more than once
- means not present
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15. Simple Types
Attributes must be Simple Types; Elements can be complex types or simple types
Simple types cannot themselves have attributes or contain other elements
The xsd:restriction tag allows you to build new simple types by adding constraints to existing simple types. These constraints are specified by a set of “constraining facets”
xsd:minInclusive and xsd:maxInclusive restrict <= myInteger <= 99999
xsd:pattern restricts using a regular expression to 3 single digits followed by two capital letters
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16. Constraining Facets
These are defined in and are
length, minLength, maxLength, pattern, enumeration, whiteSpace, maxInclusive, maxExclusive, minExclusive, minInclusive, precision, scale, encoding, duration, period
Tables tell you which constraining facets can be used with which simple type
enumeration can be used with all simple types except boolean. In example below, you could define a USState simple type which could take any of conventional abbreviations of the US States
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17. Simple Types Built In to XML Schema I
Simple Type Examples (delimited by commas) Red is Note
string Confirm this is electric
CDATA Confirm this is electric (white space(tabs) to blanks etc.)
token Confirm this is electric (trailing/leading white space removed)
byte , 126
unsignedByte , 126
binary E617279
integer , -1, 0, 1,
positiveInteger ,
negativeInteger , -1
nonNegativeInteger 0, 1,
nonPositiveInteger , -1, 0
int ,
unsignedInt ,
long ,
unsignedLong ,
short , 12678
unsignedShort , 12678
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18. Simple Types Built In to XML Schema II
decimal , 0, 123.4,
float INF, -1E4, -0, 0, 12.78E-2, 12, INF, NaN
double INF, -1E4, -0, 0, 12.78E-2, 12, INF, NaN
boolean true, false
time :20:00.000, 13:20: :00
timeInstant T13:20: :00 [May 31st 1999 at 1.20pm Eastern Standard Time which is 5 hours behind Coordinated Universal Time]
timePeriod T13:20
timeDuration P1Y2M3DT10H30M12.3S [1 year, 2 months, 3 days, 10 hours, 30 minutes, 12.3 seconds]
date
month [May 1999]
year [1999]
century [the 1900's]
recurringDay [every 31st day]
recurringDate [every May 31st]
recurringDuration T13:20: [May 31st every year at 1.20pm Coordinated Universal Time, format similar to timeInstant]
Red is Note
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19. Simple Types Built In to XML Schema III
Simple Type Examples (delimited by commas) Notes in []
Name shipTo [XML 1.0 Name type]
QName po:USAddress [XML Namespace QName]
NCName USAddress [XML Namespace NCName, i.e. a QName without the prefix and colon]
uriReference
language en-GB, en-US, fr [valid values for xml:lang as defined in XML 1.0]
ID [XML 1.0 ID attribute type]
IDREF [XML 1.0 IDREF attribute type]
IDREFS [XML 1.0 IDREFS attribute type]
ENTITY [XML 1.0 ENTITY attribute type]
ENTITIES [XML 1.0 ENTITIES attribute type]
NOTATION [XML 1.0 NOTATION attribute type]
NMTOKEN US, Brésil [XML 1.0 NMTOKEN attribute type]
NMTOKENS US UK, Brésil Canada Mexique [XML 1.0 NMTOKENS attribute type, i.e. a whitespace separated list of NMTOKEN's]
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20. List Types
List types are gotten from Simple types as white space separated atomic types
NMTOKENS IDREFS and ENTITIES are built-in list types
<listofMyInt> </listofMyInt>
Length, minLength, maxLength and enumeration are good facets of list types
<sixStates>PA NY CA FL LA AK</sixStates> is an example
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21. Anonymous and Union types
Union types define elements or attributes whose value can fall in union of one or more atomic types
Anonymous types are declared as for item and quantity in our earlier example without a type attribute
Examples: <zips>CA</zips> <zips> </zips>
Use <xsd:complexType>
Or <xsd:simpleType> after an xsd:element tag without a type= attribute
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22. Adding Attributes to Simple Types
We used <xsd:element name="USPrice" type="xsd:decimal"/> in po.xsd. Suppose we wish to give this an attribute to specify currency. This is done by deriving a new complex type from the simple type decimal
internationalPrice is defined as an anonymous type by
With example <internationalPrice currency=“EUR” >123.4 </internationalPrice>
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23. Mixed Content
The mixed=“true” attribute in xsd:complexType allows one to specify an XML element that meaningfully mixes character data with elements as in example
This schema defines two mixed contents elements salutation and letterbody.
Note order must be correct and is checked on validation
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24. Just Attributes. Empty Content
<internationalPrice currency=“EUR” value=“123.4” /> can be defined in two ways
Note use of xsd:anyType in full form as we are defining an element with no content – therefore type irrelevant.
By definition anyType puts no constraints on the content model
This is equivalent to top form
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25. Annotations
Here <xsd:annotation> with sub element <xsd:documentation> is used to explain schema of internationalPrice
Can also use xsd:appInfo element as a child of xsd:annotation to provide information to tools and stylesheets
<xsd:annotation> can appear in most Schema xsd: elements
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26. Generalized Groups
<xsd:sequence> is rather strict as it requires order of elements declared within sequence.
Some flexibility is allowed from minOccurs and maxOccurs
<xsd:choice> with <xsd:group> and <xsd:all> allow more general structures
This allows either a single address <singleUSAddress> or separate shipTo
and billTo addresses
This is the shipAndBill group referenced with ref= above
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27. The <xsd:all> Group
<xsd:all> MUST appear at top-level of any content model and the the elements in the all group must have minOccurs and maxOccurs as 0 or 1
Elements in all group can appear in any order
Top of Content Model for PurchaseOrderType
Here <xsd:all> is NOT at top
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28. Attribute Groups
Often one wishes to use the same attributes in several elements
This is done using parameter entities in DTD syntax.
Rather than “crude” macro substitution, Schema allows groups to be defined and referenced
New Attributes
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29. Use of Attribute Groups
Note Attribute declarations and attributeGroup references must appear at end of a complexType definition
Reference attributeGroup
Define attributeGroup
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30. Null Values
As well as setting explicit values for an element, one may wish to indicate that element has NO set value
Taking example of shipDate (which was absent for the Lawnmower in po.xml), one indicates this that is allowed in Schema definition by <xsd:element name="shipDate" type="xsd:date" nullable="true"/>
And to explicitly represent that shipDate has a null value in the instance document, we set the null attribute (from the XML Schema namespace for instances) to true:
<shipDate xsi:null="true"></shipDate>
This assumes one has set xmlns:xsi =
Such null values MUST not values set in <shipDate ..></shipDate> but can have any allowed attributes
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31. Schema and Namespaces I
Schema do a better job than DTD in making it clear how Namespaces can be used effectively
Here we define as the targetNamespace for this schema
We also define po: as the same URL and the default Namespace to be W3C Schema central
Then we do NOT need xsd: as in original po.xml as we have default Schema central to be default
In name=‘..’, we do NOT need to specify a Namespace but in type=“..” or ref=“..” we do not as these could reference another Namespace
No Namespace as string type define in Schema Central
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32. Schema and Namespaces II
We must distinguish global and local elements
The attribute definitions in po1.xml elementFormDefault="unqualified" attributeFormDefault="unqualified“
Imply that all local elements are assumed to come from targetNamespace and MUST not be qualified
purchaseOrder and comment are global; remainder local
apo: must be used with global elements but not with other ones
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33. elementFormDefault I Schema
We can require local elements to be qualified by setting elementFormDefault as “qualified” Attributes need not be qualified as we left attributeFormDefault as “unqualified”
Schema
Example of this Schema
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34. elementFormDefault II
If we make po1.xml the default Namespace, then whatever setting of elementFormDefault we need no prefixes at all.
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35. Selective Qualification
One can set defaults and then override defaults for selected attributes or elements
This is illustrated for attribute publicKey here
Qualification and its default is to be designed to ensure no ambiguities and mistakes when there are multiple Namespaces
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36. Global Elements in Schema
We can make schema where all elements and attributes are global as in this po.xsd
This is just the DTD “style” and all element names must be unique and all must be qualified unless po.xml is declared the default Namespace
We will find that global elements can be re-used more effectively
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37. xsd:include Tag
Here we include another schema file which itself is a valid schema definition.
The net result is a single Namespace referenced through original file
One can any number of include statements and arbitrary nesting but there will always be a single Namespace
<include schemaLocation= "
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38. xsd:Include Here is the File to be included
The parser will find all the files and construct the total Schema
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39. Deriving Types by Extension
Derived
Derived
Equivalent to
Standalone
Here the types USAddress and UKAddress are gotten by adding elements and attribute (for UKAddress) to complex type Address
ipo is defined as Namespace where UKPostcode and USAddress are defined
There is an equivalent standalone way of doing this which is shorter perhaps but as we see on next foil is less powerful in the long run
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40. Using Extended types
One can use derived types in an instance of a Schema where Schema specified only the parent
To do this you must set the xsi:type attribute for the derived element to be ipo:derived type
Here xsi is W3C central XML Schema Instance namespace.
ipo is Namespace for this particular schema
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41. Restriction of Complex Types
Here we are taking a given complex or simple type and restricting it to a subset of its previous capabilities. In example, we take Items and derive a new type ConfirmedItems which only has one change
minOccurs=“1” not “0” for the item subelement
Note you must repeat all the unchanged parts of items and item
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42. Examples of Restrictions
Valid restrictions must decrease allowed range so that if in original (minOccurs,maxOccurs) = (1,1) one cannot further restrict it
The first three examples are in common between attributes ( where one needs to specify use and value) and elements
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43. <xsd:redefine Tag
Here you do not create new elements but rather change an existing element preserving its name
Here we change Address
This change holds for all derived types based on this changed element
So UKAddress also gets a country element
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44. Substitution Groups
Consider any global element, such as comment in po.xml. We can define alternative labels for this tag with the substitutionGroup attribute in <xsd:element
One can use the new labels to improve readability of an XML instance
We define alternatives customerComment and shipComment
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45. Abstract Element and Type
If we declare comment as abstract by <element name="comment" type="string" abstract="true"/> Then we cannot use comment but we can use any element defined in a substitutionGroup such as customerComment and shipComment
Vehicle is described as an abstract type. One can use conventionally any types like Car or Plane derived from it. Element transport is defined with a type Vehicle that is abstract. Using an element with an abstract type requires setting xsi:type=“XXX” where XXX is a non abstract type derived from original one
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46. Restricting what can be changed I
One can control how much freedom there is in extending or restricting simple and complex types by use of the final attribute in the <xsd:element <xsd:complexType or <xsd:simpleType Schema elements
This stops derivation of this type later in Schema
final=“restriction” prevents new types gotten by restricting original type
final=“extension” prevents new types gotten by extending original type
final=“#all” prevents restriction and extension
In xsd:schema the attribute finalDefault can be used with these same three values to preset values of final in element and type definitions
In example, the derivation of USAddress and UKAddress would not be allowed
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47. Restricting what can be changed II
We also described how one can use in instance documents, derivations such as USAddress and UKAddress as in shipTo and billTo elements which are defined in the schema to have type Address
This capability can be controlled using the block attribute
block can take values restriction, extension or substitution (to forbid use of substitution groups) or #all to reflect all of these three capabilities
As with final, one can specify blockDefault in the <xsd:schema element to apply a default to block in every type and element definition
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48. Changing Facets in Simple Types
One can use the fixed attribute to control restriction of simple types as in this Postcode example
[A-Z]{2}\d\s\d[A-Z]{2} is an allowed derived type as length still 7
However changing length or specifying a pattern that is not 7 in length is illegal
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49. Constrained Data
This example shows a report where there are some implicit constraints
Each Zip code occurs only once
Each part can occur in different zip codes but any part occurring in any zip code must occur once and only once in <parts> section
These are constraints between different element and attribute values
With facets, we constrained individual entries.
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50. Report Schema report.xsd I
The <xsd:unique tag with name dummy1 specifies a set of elements – those in regions/zip defined on next page.
The <xsd:field tag tells you what has to be unique in this set of elements
Namely the code attribute
We will do xpath later
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51. Report Schema report.xsd II
Here we illustrate a more powerful concept which generalizes ID and IDREF in basic XML to any attribute or element
The <xsd:key tag identifies the number part element in parts as a key (generalized ID) to be referenced by pNumKey ( a generalized IDREF)
As it is a key, the number attribute in parts/part must be unique as is ID in XML specification
The <xsd:keyref tag specifies the number attribute in zip/part has properties of IDREF
It is not necessarily unique but must reference a “pNumKey” with its value
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52. Report Schema report.xsd III
This is rest of report.xsd
We can specify two fields in dummy1 to ensure that pair (zip,part) is unique
i.e. for each zip, each part occurs 0 or 1 times
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53. Import directive I In report.xsd we started schema specification
<schema targetNamespace=" xmlns=" xmlns:r=" xmlns:xipo=" elementFormDefault="qualified“ >
<import namespace="
include (as used in ipo.xsd to include address.xsd) incorporates external schema components into same target namespace as base schema.
import allows us to set up “libraries” and use predefined components from different target namespaces
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54. Import directive II
Here we see <xsd:include used earlier in ipo.xsd
Given we have imported all of ipo.xsd, we can reference any globally defined component
Thus we can write in report.xsd <element ref="xipo:comment"/>
Note however, that we cannot reuse the shipTo element from po.xsd as only global components can be used. Thus one canNOT write <element ref="xipo:shipTo"/>
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55. Import directive III
One can import complex types as long as they are globally defined
USAddress can be used from ipo.xsd and in example we extend it to Analyst type which is used to define in obvious way (not shown) an analyst element used as shown
When schema components are imported from multiple namespaces, each namespace must be identified with a separate import element, which must appear as the first children of the schema element. One must also associate each namespace with a prefix, using a standard xmlns:prefix namespace declaration. This prefix is used in any references to components in the imported namespace
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56. Type Library
Here we define a type library and access it to form a new element as shown in this Schema fragment
<schema targetNamespace= " xmlns="
xmlns:m=“ >
<import namespace=“
<element name="convertFrom" type="m:Currency" > …
</schema>
In an instance we would use:
<convertFrom name="AFA"/>199.37</convertFrom>
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57. Use of any Element in Schema
Here we introduce a new element <xsd:any with two special attributes namespace and processContents
In this example a single element <htmlexample is allowed but it is allowed to have any tags from the XHTML Namespace
processContents is set to skip so that the XHTML must be well formed but is not validated
processContents can also be strict to require validation of XHTML fragment or
processContents can also be lax when XML parser does its best
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58. any Schema Element - Example
This is an example with inserted XHTML. Note use of default Namespace in <table tag so we can avoid any prefixes
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59. any Schema Attribute or Element
The namespace attribute in <xsd:any can take several values with ##any ##local ##other and ##targetNamespace having special meaning
One can also define <xsd:anyAttribute with the example allowing href to appear in <htmlExample tag
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60. schemaLocation and xsi:schemaLocation
One can use in <xsd:schema the attribute xsi:schemaLocation to specify helpful information to parser. The syntax is xsi:schemaLocation=“Namespace1 Hint1 Namespace2 Hint2”
The parser is allowed to ignore the hints.
For a document without a target namespace use xsi:noNamespaceSchemaLocation
In import and include, the schemaLocation attribute (no xsi: prefix) specifies URI for imported/included Schema
Example of use of xsi:schemaLocation
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