XML. XML Namespaces, XML Schema, XSLT

Transcription

1 XML XML Namespaces, XML Schema, XSLT

2 Contents XML Namespaces... 2 Namespace Prefixes and Declaration... 3 Multiple Namespace Declarations... 4 Declaring Namespaces in the Root Element... 5 Default Namespaces... 6 XML Schema Overview... 7 Associating XML with a Schema... 8 Simple and Built-in Types... 9 Complex Types Element Declarations Attribute Declarations Choices Named Types and Anonymous Types XSL Transformation (XSLT) XPath Basics xsl:stylesheet xsl:template xsl:value-of xsl:apply-templates xsl:output XML Namespaces Exercises XML Schema Exercises XSLT Exercises

3 XML Namespaces You can use namespaces to declare that your document is using a vocabulary from a different technology. o A program that understands the meaning of a particular namespace name can then identify and make use of the prefixed elements from the referenced vocabulary. o We will investigate examples of using namespaces for this purpose when we discuss XSLT and XML Schema. Another use of namespaces is to avoid naming ambiguities in your elements and attributes. o Often, a similar concept might warrant a similar tag name in multiple locations of a document. This can be avoided when first creating a model of XML for your document. However, when building up XML from smaller existing XML fragments, this issue is more likely to occur. o Name collisions can occur if two XML fragments each contain a tag with the same name. 2

4 Namespace Prefixes and Declaration Every element or attribute that should be associated with a namespace should be given a prefix. <emp:title>librarian</emp:title> o The part before the colon is called the prefix. o The part after the colon is called the local name. o The whole tag, including the prefix and local name, is referred to as the qualified name or qname. The prefix must be declared with the reserved xmlns attribute. <emp:staff xmlns:emp=" o This associates the prefixed elements with the quoted namespace name. Since Uniform Resource Identifiers (URIs) are unique across the Internet, they are the recommended choice for namespace names. o The namespace name should uniquely identify the context in which the tags have meaning. o The URI does not have to actually point to a real resource. 3

5 Multiple Namespace Declarations You are allowed to declare multiple namespaces within the same document. o Each namespace declaration is made with the reserved xmlns attribute and a unique prefix. The element and any attributes at the level of a namespace declaration do not automatically belong to that namespace. They can use the prefix to qualify themselves to the namespace. Descendant elements and their attributes do not automatically belong to that namespace, but they too can use the prefix. 4

6 Declaring Namespaces in the Root Element It is common to move most, if not all, namespace declarations to the root element. o This allows any element or attribute within the document to use the declared prefix. o It also simplifies maintenance. A given namespace name is only declared once. It is easy to find the namespace declarations. It is not a requirement to make the root element belong to any of the namespaces that are declared in its attributes. o A non-prefixed element does not belong to any namespace. 5

7 Default Namespaces You can declare a default namespace for an element and its descendants. <library xmlns=" o The element and its descendants will be considered part of the given namespace, with no need for a prefix. o The default namespace is only applicable to non-prefixed elements. Non-prefixed attributes do not belong to the default namespace. An element is considered to be qualified if it belongs to a namespace. o With default namespaces, it is now possible to have qualified, non- prefixed elements. 6

8 XML Schema Overview XML Schema is a W3C specification for validating the content of an XML document. Schema documents are modeled in XML syntax. o The schema must be well-formed. Associate your schema with the namespace name: By convention, the prefix xsd or xs is used. Any element or attribute within the document that uses the prefix will be associated with the schema vocabulary, as opposed to the document author's vocabulary. Every schema must define a root element named schema. Within the root element, there will be a variety of subelements, including element, complextype, and simpletype. All children of the schema element are called globals. o Any global element is eligible to be the root element of the XML document to be validated. o Only globals can be referenced from elsewhere within the document. 7

9 Associating XML with a Schema An XML document can explicitly indicate when it can be validated against an XML Schema. o The XML Schema is an external document and is often referred to as the schema definition file. If the XML document to be validated (the instance document) does not use a namespace, then associating it with a schema is simple. o Declare the XMLSchema-instance namespace. o Define the nonamespaceschemalocation attribute to the URI of the schema document. <rootelement xmlns:xsi=" xsi:nonamespaceschemalocation="schemadocument.xsd"> 8

10 Simple and Built-in Types A simple type can only contain numbers and strings, but not subelements nor attributes. There are a number of simple types that are built in to the schema definition. o string, int, decimal, and date are all examples of another simple type. o An element that is of type int, for example, has a value between and Use the restriction element to derive a custom simple type from another simple type. o The base attribute specifies which datatype will be restricted. The datatype can be a built-in type or another simple type defined o elsewhere. Add facet subelements to the restriction element. A facet is a kind of restriction that is applied to a datatype. 9

11 Complex Types A complex type can contain subelements and/or attributes. Use the complextype element to model a complex type. <xsd:complextype name="patienttype"> <xsd:sequence> <xsd:element name="fname" type="xsd:string" /> <xsd:element name="lname" type="xsd:string" /> </xsd:sequence> <xsd:attribute name="status" type="xsd:string" /> </xsd:complextype> Add each subelement within the complex type as the child of a sequence, choice, or all element. o The order of each element within the sequence is the order in which they must appear in the resulting document. o If order does not matter, use all instead of sequence. o Use choice to model a choice of one element. A valid instance document is limited to only one of the child elements of the choice tag. Model attributes by using the attribute element. o Attributes are defined after all element definitions. To model an empty element, omit the sequence/choice/all tags. o Use the attribute element as before to specify attributes for the empty element. 10

12 Element Declarations Declare an element using the element named element. <xsd:element name="zipcode" type="xsd:string" /> o The type can be any simple or complex type. Use the ref attribute to refer to a global element that was defined elsewhere. <xsd:element ref="zipcode" /> o Global elements are child declarations of a schema. To specify how many times an element may occur, use minoccurs or maxoccurs. <xsd:element name="street" type="xsd:string" minoccurs="1" maxoccurs="2"/> o By default, minoccurs is 1 and maxoccurs is 1. o You can use unbounded for maxoccurs to specify that there may be unlimited occurrences of this element. Use the default attribute to specify a default value for the element if it appears in the document without any content (an empty element). <xsd:element name="name" type="xsd:string" default="john Doe"/> Use fixed to specify that an element must contain a particular value. <xsd:element name="state" type="xsd:string" fixed="co"/> 11

13 Attribute Declarations Declare an attribute using the attribute element. <xsd:attribute name="info" type="xsd:string" /> o Since attributes cannot contain subelements or attributes, the type can only be a simple type. o Place the attribute declaration at the end of a complextype declaration. Use default and fixed attributes similar to how they are used for elements. o Note that a default value for an attribute is inserted any time the attribute is omitted, whereas for an element it is only inserted when that element is empty. Instead of minoccurs or maxoccurs, declare the use attribute to handle occurrence constraints. o use="required" specifies that the attribute must be in the XML document. o use="optional" says that the attribute may or may not occur in the XML document. o use="prohibited" means that the attribute may not be in the XML document. o If an attribute has a default value, then it can only specify the value of optional for use. 12

14 Choices It may be necessary to specify a set of choices for the value of an element or attribute. o Use enumeration facets to specify the set of choices. <xsd:simpletype name="housetype"> <xsd:restriction base="xsd:string"> <xsd:enumeration value="ranch"/> <xsd:enumeration value="two-story"/> <xsd:enumeration value="bi-level"/> </xsd:restriction> </xsd:simpletype> 13

15 Named Types and Anonymous Types You can create schemas so that each complex type or derived simple type has a name. o These are referred to as named types. o Each named type is referenced by using type= syntax in elements and attributes. o Named types can get out of control if a schema has many types that are referenced only once. You can use anonymous types as an alternative. o Anonymous types do not include names, nor do they need to be referenced. o The lack of a name or type= syntax identifies an anonymous type. o An anonymous type uses containment to model both complex and derived simple types. o Since anonymous types don't have names, they can't be referenced from elsewhere. 14

16 XSL Transformation (XSLT) Extensible Stylesheet Language Transformation (XSLT) is about transforming XML documents into other other formats. o An XSLT stylesheet is an XML document that spells out the rules of a particular transformation. An XSLT processor parses the XML document, applies the rules of the stylesheet to convert the document. o This can be another XML document, an HTML document, or plain text. XSL-FO is an XML technology that can be leveraged to produce more complex types of documents, like PDF or RTF. Stylesheet elements must be associated with the namespace /XSL/Transform. A processor can be applied directly within a web browser. o The browser downloads the XML source, applies the stylesheet, and displays the result. o Browsers recognize the xml-stylesheet processing instruction, and use it to associate the XML file with a particular stylesheet. <?xml-stylesheet type="text/xsl" href="example.xsl"?> 15

17 XPath Basics Many XSLT elements use XPath to specify the pattern for matching or selecting a node or group of nodes. XPath views an XML document as a tree with different node types, and uses different constructs to select them. o Use / to identify the root node, which is the root of the source tree, not the root element. o Use the element name to identify an element. o Identify an attribute o Select all elements at the specified point in the tree with * and all attributes XPath patterns can include navigation of the document's tree. o Pattern matches start from the current node location or context. o A leading slash (/) forces the search from the root node and other slashes act as level separators. o. matches the current node and.. matches the parent node. o acts as an "or," allowing you to select nodes matching any of the specified patterns. A predicate allows conditions inside of a trailing [ ] to further limit the collection of nodes matched by the expression. 16

18 xsl:stylesheet The root element of a stylesheet is xsl:stylesheet. <xsl:stylesheet version="2.0" xmlns:xsl=" o Include the namespace declaration. xsl is the namespace prefix by convention only. o A version attribute is required. Many elements are allowed as children of xsl:stylesheet. o These are called top-level elements and can include: o import and include elements to use other stylesheets o An output element to specify the type of output document o template elements Other than having any import children occur first, ordering of top-level elements is arbitrary. The XSLT namespace offers the alternative root element xsl:transform. o There is no difference between xsl:stylesheet and xsl:transform. 17

19 xsl:template A template is an XSLT element that defines a translation rule. o Many templates can exist within the same document. Define a template with the xsl:template element. <xsl:template match="pattern"> content </xsl:template> o Use the match attribute to define an XPath expression which indicates the nodes to which this template could apply. o Non-XSLT element and text content are moved into the result tree. o XSLT child element content is processed according to the element rules. Most stylesheets have at least one xsl:template element the root template. o The value of the match attribute is /, which is the XPath syntax for the root node. <xsl:template match="/"> 18

20 xsl:value-of Use xsl:value-of to move XML source text to the result tree. o This will be a subelement of xsl:template. o The select attribute specifies an XPath pattern to the element of interest. <xsl:value-of select="element-pattern"/> The value of the select attribute is an XPath expression starting from the perspective of the template that is being processed. o If the selected element contains character data, that string is returned. o If the selected element contains additional subelements, a concatenation of all descendant character data is produced. Depending on the nature of your XML, you might need to employ the XPath text() function to navigate directly to an element's text node. <xsl:value-of select="element-pattern/text()"/> o Retrieve attribute values by prepending character to the attribute name within the pattern. <xsl:value-of select="attribute-path/@attribute-name"/> 19

21 xsl:apply-templates To process a template other than the root template, use xsl:apply-templates. o Use xsl:apply-templates from within an xsl:template. Use the select attribute to define an XPath expression which indicates the nodes that need processing through another template. <xsl:apply-templates select="mypattern"/> o If the select attribute is omitted, it is equivalent to select="node()". When the XSLT processor identifies an xsl:apply-templates element, it applies any templates that match the select attribute. <xsl:template match="matchingpattern"> actions </xsl:template> o When there are multiple nodes that match the selection in the source tree, the processor repeats the template for each node. The xsl:apply-templates facility provides a motivation for having multiple templates in your stylesheet. o Template order is arbitrary. o Each template will have its own default node context from which further XPath evaluations begin. 20

22 xsl:output Standard XSLT processors can create XML, HTML, or text output. Specify the output type with the xsl:output element and the respective value on the method attribute. <xsl:output method="xml"/> xsl:output needs to be a top-level XSLT element. Without an xsl:output element, the default document type will be XML. However, if the result document begins with html, the default document type will be HTML. When creating an HTML document, the stylesheet needs to use XHTML. o XHTML is well-formed, keeping the stylesheet well-formed. o The resulting document, however, will be HTML, not XHTML. If you want the resulting document to be XHTML, then set the xsl:output element attribute value to "xml". 21

23 XML Namespaces Exercises 5 to 15 minutes 1. Change the document homepage.xml so that all news elements belong to a namespace. 2. Update your document from 1. by adding a namespace to all sports elements. 3. Update your document from 2. so that it uses a default namespace for all tags that do not currently belong to a namespace. 22

24 XML Schema Exercises 20 to 30 minutes 1. Define the nonamespaceschemalocation attribute to the URI of patient.xml and validate the document. <?xml version='1.0'?> <patient xmlns:xsi=" xsi:nonamespaceschemalocation="patient.xsd"> Sam Smith </patient> 2. Add an element medication with subelements id and drug to patient.xml and validate the document. Note the error message that occurs.what is wrong? <?xml version='1.0'?> <patient xmlns:xsi=" xsi:nonamespaceschemalocation="patient.xsd"> <id> </id> <name>sam Smith</name> <medication> <id>med4512</id> <drug>aspirin</drug> </medication> </patient> 23

25 3. Declare 2 complex types PatientType and MedicationType to patient.xsd and change the type of the patient element to PatientType. Validate patient.xml. <?xml version='1.0'?> <xsd:schema xmlns:xsd=" <xsd:element name="patient" type="patienttype" /> <xsd:complextype name="patienttype"> <xsd:sequence> <xsd:element name="id" type="xsd:string" /> <xsd:element name="name" type="xsd:string" /> <xsd:element name="medication" type="medicationtype"/> </xsd:sequence> </xsd:complextype> <xsd:complextype name="medicationtype"> <xsd:all> <xsd:element name="id" type="xsd:string" /> <xsd:element name="drug" type="xsd:string" /> </xsd:all> </xsd:complextype> </xsd:schema> 4. Declare a global element named id of type xsd:string in patient.xsd and refer all other id elements to this global element. Also specify how many times the medication element may occur using minoccurs and maxoccurs. Validate patient.xml. <?xml version='1.0'?> <xsd:schema xmlns:xsd=" <xsd:element name="patient" type="patienttype" /> <xsd:element name="id" type="xsd:string" /> <xsd:complextype name="patienttype"> <xsd:sequence> <xsd:element ref="id"/> <xsd:element name="name" type="xsd:string" /> <xsd:element name="medication" type="medicationtype" minoccurs="0" maxoccurs="unbounded" /> </xsd:sequence> </xsd:complextype> <xsd:complextype name="medicationtype"> <xsd:sequence> <xsd:element ref="id"/> <xsd:element name="drug" type="xsd:string" /> </xsd:sequence> </xsd:complextype> </xsd:schema> 24

26 5. Add an attribute named condition with value fair to the root element patient in patient.xml. Declare an attribute named condition in patient.xsd of type xsd:string and add attributes use and default. Validate patient.xml. patient.xml <?xml version='1.0'?> <patient xmlns:xsi=" xsi:nonamespaceschemalocation="patient.xsd" condition="fair"> <id> </id> <name>sam Smith</name> <medication> <id>med4512</id> <drug>aspirin</drug> </medication> <medication> <id>med4598</id> <drug>ibuprofen</drug> </medication> </patient> patient.xsd <?xml version='1.0'?> <xsd:schema xmlns:xsd=" <xsd:element name="patient" type="patienttype" /> <xsd:element name="id" type="xsd:string" /> <xsd:complextype name="patienttype"> <xsd:sequence> <xsd:element ref="id"/> <xsd:element name="name" type="xsd:string" /> <xsd:element name="medication" type="medicationtype" minoccurs="0" maxoccurs="unbounded" /> </xsd:sequence> <xsd:attribute name="condition" type="xsd:string" use="optional" default="critical" /> </xsd:complextype> <xsd:complextype name="medicationtype"> <xsd:sequence> <xsd:element ref="id"/> <xsd:element name="drug" type="xsd:string" /> </xsd:sequence> </xsd:complextype> </xsd:schema> 25

27 6. Specify a set of choices for the condition attribute by creating a simpletype named ConditionsType in patient.xsd. Validate patient.xml <?xml version='1.0'?> <xsd:schema xmlns:xsd=" <xsd:element name="patient" type="patienttype" /> <xsd:element name="id" type="xsd:string" /> <xsd:complextype name="patienttype"> <xsd:sequence> <xsd:element ref="id"/> <xsd:element name="name" type="xsd:string" /> <xsd:element name="medication" type="medicationtype" minoccurs="0" maxoccurs="unbounded" /> </xsd:sequence> <xsd:attribute name="condition" type="conditionstype" use="optional" default="critical" /> </xsd:complextype> <xsd:simpletype name="conditionstype"> <xsd:restriction base="xsd:string"> <xsd:enumeration value="critical" /> <xsd:enumeration value="serious" /> <xsd:enumeration value="fair" /> <xsd:enumeration value="good" /> </xsd:restriction> </xsd:simpletype> <xsd:complextype name="medicationtype"> <xsd:sequence> <xsd:element ref="id"/> <xsd:element name="drug" type="xsd:string" /> </xsd:sequence> </xsd:complextype> </xsd:schema> 7. Update patient.xml so that each medication also has dosage information. Include amount (number of pills to take), units (i.e. 100mg), start date, frequency (how many times to take the medication each day), and duration. 8. Modify patient.xsd to validate your XML. 9. Create a new file named person.xsd and build a schema to model a person. Include first name, last name, middle initial, address, and phone. 10. Write a valid XML document named person.xml that uses your schema defined in person.xsd. Challenge 11. Write a schema in a new file named invoice.xsd to describe an invoice: 26

28 a. The invoice should have a company name, date, shipping method, customer information, payment information, and one or more items. b. For the shipping method, use attributes to specify the two options: UPS or FedEx. Make UPS the default. c. The customer information should include a customer id, optional firstname, lastname, address, and zero or more area code and phone number combinations. For every phone number, include an attribute that describes it, using one of the following: home, work, fax, pager, or cell. The default is home. d. The payment information should allow for either checks or credit cards. A check should have an optional attribute for the check number. A credit card should have an attribute for the credit card type and child elements for the card number and the expiration date. The credit card type must be given and can only be one of the following: Visa, AmEx, or MC. e. Finally, each item has a quantity, part number and unit price. Also add an optional attribute to the item for a description of the item. 12. Modify invoice.xml so that it validates against the schema you created in

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30 XSLT Exercises 15 to 25 minutes 1. Add a stylesheet element to the garage.xsl document: <?xml version="1.0"?> <xsl:stylesheet version="2.0" xmlns:xsl=" <html><body><div align="center"> <h1>stuff in my Garage</h1> <table border="1"> <tr> <td>year</td><td>make</td><td>model</td><td>miles</td> </tr> </table> </div></body></html> </xsl:stylesheet> 2. Add the root template to your garage.xsl document. Then process garage.xml by opening it in a browser or Notepad++. Note that although we are transforming the garage XML data, none of the actual XML data is included in the output at this point. <?xml version="1.0"?> <xsl:stylesheet version="2.0" xmlns:xsl=" <xsl:template match="/"> <html><body><div align="center"> <h1>stuff in my Garage</h1> <table border="1"> <tr> <td>year</td><td>make</td><td>model</td><td>miles</td> </tr> </table> </div></body></html> </xsl:template> </xsl:stylesheet> 29

31 3. Add multiple xsl:value-of elements to garage.xsl in order to extract the text of the year, make, model, and miles associated with the cars of your garage. Do this within the root template. Because the context of the root template is the root node, the XPath expressions will have to include the navigation through the garage and car elements. <?xml version="1.0"?> <xsl:stylesheet version="2.0" xmlns:xsl=" <xsl:template match="/"> <html><body><div align="center"> <h1>stuff in my Garage</h1> <table border="1"> <tr> <td>year</td><td>make</td><td>model</td><td>miles</td> </tr> <tr> <td><xsl:value-of select="garage/car/year"/></td> <td><xsl:value-of select="garage/car/make"/></td> <td><xsl:value-of select="garage/car/model"/></td> <td><xsl:value-of </tr> </table> </div></body></html> </xsl:template> </xsl:stylesheet> Refresh your browser or run the transformation again and note the result. You should observe that with the XSLT rules we have available at this point, we are only extracting the data associated with the first car of the garage. Clearly, we will want to find a way to work with all of the vehicles in the garage. 30

32 4. Edit garage.xsl to create a new template that would handle each car or van that is a subelement of the garage. This template should extract the values of the car or van into a row of an HTML table. Further edit the same file to update the root template. The root template should start the table, including the header row, and then apply the new template for each car and van. <?xml version="1.0"?> <xsl:stylesheet version="2.0" xmlns:xsl=" <xsl:template match="/"> <html><body><div align="center"> <h1>stuff in my Garage</h1> <table border="1"> <tr> <td>year</td><td>make</td><td>model</td><td>miles</td> </tr> <xsl:apply-templates select="garage/*"/> </table> </div></body></html> <xsl:template match="car van"> <tr> <td><xsl:value-of select="garage/car/year"/></td> <td><xsl:value-of select="garage/car/make"/></td> <td><xsl:value-of select="garage/car/model"/></td> <td><xsl:value-of select="garage/car/@miles"/></td> </tr> </xsl:template> </xsl:stylesheet> Run the transformation again by refreshing your browser and note that all of the garaged cars and vans are included as part of the output. 5. Transform menu.xml into an HTML document that presents a grocery list of ingredients. Challenge 6. Transform menu.xml into an HTML document that presents a recipe list in tables. 7. Transform menu.xml into an HTML document that presents a menu for our customers. 31