Page tree
Skip to end of metadata
Go to start of metadata

XML Namespaces

XML namespace URIs should follow the following pattern:

http://midpoint.evolveum.com/xml/ns/public|private|experimental|test/<component>/[<subcomponent>/[<subcomponent>/[...]]]/<artifact-name>-<majorversion>

public, private, experimental: the level of protection of the concepts in the namespace:

  • public: Schema, interface or concept available outside of the component or subsystem. Public interface. It should be reasonably stable. E.g. common schema, public WSDL interfaces, etc.
  • private: Concepts and schemas that are private for a specific component, that may be deployment-dependent or wiring-dependent. It may be somewhat unstable. E.g. concrete WSDL templates (including port names) and private XSD schemas.
  • experimental: Laboratory stuff. Schemas for testing new concepts, improvements, or just outright crazy ideas. These are not part of the production system. Very unstable. Handle with utmost care.

component: name of the component or subsystem or interface, e.g. repository, provisioning. For common components it should be also something meaningful, e.g. common.

subcomponent: name of a sub-component or sub-concept, e.g. idconnector

artifact-name: name of the file, schema or concept. E.g. identity, model, etc. Multiple words should be separated by dashes (-) if needed.

majorversion: number specifying major version. It will change if there is an incompatible change to the schema. Minor version should not be part of XML namespace as changing a minor version should be compatible change and therefore must not break existing code (and namespace URI is part of the code). Technically, the actual value of the version number does not matter as long as it is changed to a unique value in case of non-compatible change. However, the version number should be numeric and increasing in time.

Namespace names should be composed only from lower-case letters, multiple words separated by dashes if needed. The camelCase should not be used. This approach avoids various case-sensitivity issues in various operating systems.

Only public portion of the namespace should be shared and used between components. However, there may be cases where we need to work around a specific issue and therefore also parts of the private namespace are referenced between components. These cases must be avoided if possible. If they cannot be avoided, such cases must be well documented.

Namespace Examples

URI-QName Mapping

WWW Architecture mandates that URIs and QNames are to be considered equivalent. It is not universally followed, but we should follow it. It will also help us avoid some OpenESB bugs and limitations of various components.
The QNames are mapped to URIs by concatenating namespace URI and a local name. If URI does not end with slash (/) or hash (#) character, hash (#) is concatenated to the URI before adding the local name. The URI-QName mapping is the reverse process. Local names must not contain hash or slash characters.

The namespace name should not end with hash (#) (see explanation below). XML schema, WSDL document namespace and other "abstract" definitions should not end with slash (/), so the hash (#) is assumed at the end. All the QNames used in such "abstract" definitions there are included in the same document and a single fetch of the schema is sufficient to fetch them all. The hash character in URI is specifying just that.

Namespace components (names) should be in lowerCamelCase. Spaces or special characters should not be used. Create namespace names in a simple way to avoid need for URI escaping by even the most paranoid software components.

TODO: the mapping is not entirely reversible, (in case of trailing # in namespace)

URI-QName Mapping

XML Schemas

XML Element names, WSDL message names, parts and similar "concrete" parts of the definitions should be in lowerCamelCase.
XSD Types and similar "abstract" definitions should be in UpperCamelCase. The XML types should also end with "Type", e.g. UserType or ResourceObjectType.

See Also

See XML Namespace List

Additional Explanation

The namespaces are theoretically independent from the files containing the individual artifacts. But we have chosen to follow the same naming convention for directories/files and for namespaces to make things simpler. But still please do not assume that this will always be the same.

Only a major version of the artifact is propagated to the schema. Minor version is not important for compatibility and in fact can cause a lot of problems. The authoritative source of the versioning information the source code management system (SVN). Major version in the namespace should only be considered a mechanism for marking compatible and non-compatible changes to the schemas and interfaces.

The namespace name should not end with hash (#) due to a buggy software (such as some Glassfish components) that blindly append hash character to namespace when forming a QName. That results in two hashes in the URI.

  • No labels