PB138/07 - Modern Markup
Languages and Their Applications
Lab 02 [2.3.2020]
XML Schema (XSD)
Bruno Rossi
Department of Computer Systems and Communications,
Lasaris (Lab of Software Architectures and Information Systems)
Masaryk University, Brno
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●
XSD (XML Schema Definition): how to formally describe the
elements in an XML document. It is used to validate that a
specific XML conforms to the XSD definition
●
XSD: just another XML document
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="classroom" type="classroomtype" />
<xs:complexType name="classroomtype">
<xs:sequence>
<xs:element name="teacher" type="xs:string" />
<xs:element name="members" type="memberstype" maxOccurs="unbounded" />
</xs:sequence>
</xs:complexType>
....
</xs:schema>
Quick Summary (1/2)
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Quick Summary (2/2)
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Different ways to create an XSD
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See “Divide the Schema” and “Using Named Types”
https://www.w3schools.com/xml/schema_example.asp
https://www.w3schools.com/xml/schema_example.asp
1. Defining Data Types
<xs:simpleType name=”yyy”> → text, numbers, restrictions
or
<xs:complexType name=”yyy”> → other elements, attributes, text
2. Assigning Data types to elements
<xs:element name="xxx" type=”yyy”> → type is a reference to the name used to
define the type
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XML Schema (XSD)
●
We will use the same continent.xml example we used before
●
You can download the file named 02-xsd-ex.zip
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In these tasks, you will have to modify the file continent.xsd
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
</xs:schema>
●
Run xmllint to check what's the results from schema validation
using file continent.xml
$> xmllint --noout --schema continent.xsd continent.xml
We have an empty XSD, will the validation
pass?
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Exercise (1/6)
●
As you see, validation is not passing
●
Try to make the smallest change to the XSD that will make
validation pass
●
You can use
<xs:element name="xxx" type=”yyy”>
Do you need to declare the type here?
What is the type in this case?
Common types
xs:string
xs:decimal
xs:integer
xs:boolean
xs:date
xs:time
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Exercise (2/6)
●
Update the XSD to represent the structure of the XML file
Remember:
●
attributes can only be defined for complex types
<xs:attribute name="xxx" type="yyy"/>
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Manage elements occurrence with minOccurs="0..n"
maxOccurs="0..n" (maxOccurs="unbounded")
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Difference between <xs:sequence>, <xs:choice>, <xs:all>
●
Look at
https://www.w3.org/TR/xmlschema-0/ (2.1 the Purchase Order Schema)
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Exercise (3/6)
●
Try to place a restriction on the maximum population of a city
(min:0, max:14200000)
●
Consider using
<xs:restriction base="xs:integer">
<xs:minInclusive value="xxx"/>
<xs:maxInclusive value="yyy"/>
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Exercise (4/6)
●
Try to place a restriction on the type of pollution
('low','medium','high)
●
Consider using
<xs:restriction base="xs:string">
<xs:enumeration value="xxx"/>
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Exercise (5/6)
●
Try to place a restriction on initial letter of the city name: it must be
starting with capital letter (note that this should also allow cities
such as 'Los Angeles')
●
Consider using
<xs:restriction base="xs:string">
<xs:whiteSpace value="preserve"/>
<xs:pattern value="REGEXXX"/>
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Exercise (6/6)
●
Modify continent.xml to give both Tokio and Mumbai the same id:
...
<city id="1">
<name>Tokio</name>
....
</city>
<city id="1">
<name>Mumbai</name>
...
</city>
●
Check that the file still passes validation
●
Define either a key or unique constraint for the city id, the structure is:
<xs:key name="<constraint name>" >
<xs:selector xpath="<xpath selector, e.g., element>" />
<xs:field xpath="<xpath field, e.g. @attr>" />
</xs:key>
●
Validation has not to pass. You should be getting something like Element 'city':
Duplicate key-sequence ['1'] in key identity-constraint 'id'.
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For next time (optional)
Checkout the code at https://gitlab.fi.muni.cz/pb138/seminars/seminar-02
1) Use either the Java or Javascript implementation to validate the
schema created today – it should pass as with xmllint :)
2) in the src/ folder, complete schema.xsd for data.xml in similar way
we did today (you can also see a reminder of the syntax in
schema-ukazka.xsd)
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References
Suggested material:
●
W3C XML Schema Definition Language (XSD) W3C Recommendation:
→ https://www.w3.org/TR/xmlschema-0/
●
XML Schema Tutorial on w3schools.com:
→ https://www.w3schools.com/xml/schema_intro.asp