Formal Public Identifier (FPI)

Roger Costello

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Motivation

• Suppose that you create a web service. The input to the web service is the URL to an XML instance document, and an identifier of a Schematron schema:
  • http://www.example.org?xml=...&schema=???
• How do you identify the schema? That's the purpose of a Formal Public Identifier (FPI) - to provide a unique identifier of a schema.

fpi Attribute

• The root element of a Schematron schema has an optional attribute, fpi:

1. <?xml version="1.0"?>
2. <sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron"
3. fpi="...">
4. ...
5. </sch:schema>

• Identify the schema with a unique name by providing a value for the fpi attribute

Constructing a fpi

• A Formal Public Identifier has this format:
• (ISO | + | -)//schema's owner//schema description//language id
• If the schema is an ISO standard, its name begins with the string ISO. If a non-standards body has approved the schema, its name begins with a plus sign. If no standards body has approved the schema, its name begins with a hyphen.

Example

• The fpi attribute names the Schematron schema. The name indicates that the schema has not been approved by a standard's body, it was created by Roger Costello, it is the Security Classification Policy Schematron Schema, and the schema is in English:

1. <?xml version="1.0"?>
2. <sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron"
3. fpi="-//Roger Costello//Security Classification Policy Schematron Schema//EN">
4. ...
5. </sch:schema>

Recommendation

• Always use fpi to name your Schematron schemas. It will facilitate the development of web services.