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Using Namespaces in XML

Using Namespaces in XML. COIN 78 Lecture 7. Designing a namespace name. Distinguish one similarly titled element from another Unique and permanent name In XML, must have an absolute URL Use your own domain name as a root to keep control over name’s uniqueness

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Using Namespaces in XML

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  1. Using Namespaces in XML COIN 78 Lecture 7

  2. Designing a namespace name • Distinguish one similarly titled element from another • Unique and permanent name • In XML, must have an absolute URL • Use your own domain name as a root to keep control over name’s uniqueness • URL may point to a DTD or schema, but that is not required

  3. Sample code http://www.domain.com/ns/rivers/1.0 • opening protocol • your domain name • optional namespaces directory information • short description of the namespace • optional version number

  4. Declaring Default Namespaces • To declare a default namespace for an element and all its children: • Within the opening tag of an element, type: xmlns= • Then type “URL” where URL is the name of the namespace

  5. Sample code - in No Namespace <endangered_species> <animal> <name language=“English”>Giant River Otter</name> … <source sectionid=“122” newspaperid=“21” contentid=“630” xmlns=“http://www.cookwood.com/ns/end_species1” /> <picture filename=“otter.jpg” x=“200” y=“197” />

  6. Sample Code <endangered_species xmlns=“http://www.cookwood.com/ns/end_species1”>….. </endangered_species> • With the namespace declaration in the root element, all of the elements in the document are associated with the http://www.cookwood.com/ns/end_species1 namespace

  7. Namespaces for Individual Elements • To declare a prefix for a namespace name: • In the document’s root element, type xmlns:prefix where prefix will be the nickname for this namespace • Then type =“URL” where URL is the name of the namespace to which the prefix will refer

  8. Sample Code <endangered_species xmlns=“http://www.cookwood.com/ns/endspecies1” xmlns:rivers=“http://www.cookwood.com/ns/rivers1” … </endangered_species> • xmlns:rivers points to rivers1 as the namespace for the named prefix rivers

  9. How Namespaces Affect Attributes • You could associate an attribute with a specific namespace, however... • By prefixing it with appropriate prefix, it’s almost never necessary, since... • Attributes are already made unique by the element that contains them...

  10. Sample Code <source sectionid=“122” newspaperid=“21” contentid=“630” /> <orange sectionid=“3a” /> • “sectionid” does not require a separate name space • The two elements that contain it, source and orange, have no overlap

  11. Namespaces, Schemas, and Valid Documents • An element is more than its name alone • XML processors consider the element to be called prefix:element • If you want to validate the document against a schema, you must declare each prefix element in the schema • Additionally, it is necessary to declare the attribute with which you declare the namespace, either xmlns or xmlns:prefix

  12. Summary • Namespaces create super labels that can distinguish elements of similar names when two or more documents are combined. • The super label is called the namespace name • The namespace itself is the collection of related names identified by the namespace name. • Namespaces are located by URLs that point to a file with a given name. Namespaces may apply to all elements in a document or just one.

  13. Namespaces, Schemas, and Validation COIN 78 Lecture 8

  14. Schemas and Namespaces • Namespaces are a collection of related elements and attributes, identified by a common “URL-shaped” name. • Namespaces are most often used to distinguish similarly named globally declared elements from one another. • A schema can define what an XML document should look like, and can simultaneously create or populate a namespace.

  15. Populating a Namespace • You can associate the globally declared (top level) components of a schema with a namespace in order to use those components in other schema documents. • To specify a target namespace: • Type targetNamespace=“URL” • Where URL is the namespace with which you want to associate the components defined in this schema: called “populating a namespace”

  16. Adding All Locally Declared Elements • To add all the locally declared elements elements to the target namespace: • In the xsd:schema element, type elementFormDefault=“qualified”

  17. Adding Particular Locally Declared Elements • To add a particular locally declared declared element to the target namespace • In the element’s declaration, type form=“qualified” • To keep a particular locally declared element from being associated with a target namespace (despite the default) • In the element's declaration type: form=“unqualified”

  18. Referencing Components with Namespaces • To specify a default namespace for referenced components and then reference those components in the schema: • In the root element of the schema document, type xmlns=“URL” where URL is the namespace for the referenced components. • In the value of the type and ref attributes, type reference where reference is the name of the component associated with the default namespace.

  19. The Schema of Schemas as the Default • You can declare the schema of schemas as the default namespace for a schema • Type <schema (not xsd:schema) • Type xmlns=“http://www.w3.org/2001/XMLSchema • Type targetNamespace=“URL” • Type xmlns:prefix=“URL” (repeat for each name) • Type > to complete the schema tag

  20. Namespaces and Validating XML • You can qualify a set of components (identify them with a namespace) and validate a document that uses those components. • You must indicate the namespace of the desired components by either declaring a default namespace (xmlns=“URL”) or • Declaring a namespace with a prefix (xmlns:prefix=“URL”). It is sometimes necessary to indicate where the schema

  21. Indicating Where a Schema Is • In the root element of the XML document, after the declaration of the namespace type: xmlns:xsi=“http://www.w3.org/2001/XMLSchema-instance” then: xsi:schemaLocation=“URL (of the namespace) then type file.xsd” where file.xsd is the actual file that contains the schema that defines the namespace used in this XML document.

  22. Schemas in Multiple Files • You can divide a schema’s components into various individual files. Each file should be text only and saved with the .xsd extension. • Directly after xsd:schema type <xsd:include schemaLocation=“included-file.xsd” /> • Where includedfile.xsd is the URL of the schema document that contains the components you wish to include

  23. Importing Components • To import components from schemas with different target namespaces: • Directly after the xsd:schema element in the schema document into which you are importing components, type <xsd:import • Then type namespace=”URL” • Then, if needed, xsi:schemaLocation=“URL” • Then type file.xsd then /> to close xsd:import

  24. Summary • XML namespaces can be imported • Create and “qualify” schema definitions • Allows for independent development • Compartmentalization of schema files • Nomenclature in the schema document declarations is critical, keep references • Validation is still a -very- tricky issue

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