IdSchemas/Existing MetaData

(work in progress)...

Introduction
Metadata is the information used to describe schemas and elements, such as attributes, of schemas. Most identity systems that have extensible schema implement a few types of metadata. Some of these are mandatory, without which the schema cannot be understood by the identity system. There is also metadata on identity schema which is not implemented by identity systems themselves, but is descriptive and is useful for architects and schema designers.

Identity Systems with metadata of interest include:
 * Information Card - see Claim Catalog
 * OpenID - see OpenID AX (metadata)
 * SAML 2.0 attributes and assertions
 * LDAPv3
 * SPML v2.0
 * XRI/XDI
 * FOAF
 * Higgins HOWL

Related documents:
 * http://oldidschemas.idcommons.net/moin.cgi/MetaData?action=AttachFile&do=get&target=schema-metadata-existing-specs-1_0-00.html - from Sept 2007

1. Combined informal metadata table
This table merges the mandatory and optional metadata of each identity system, as well as metadata that is identity system independent.

2. Supporting tables
These tables are to help with building the above table and then turning it into one or more formal representations.

2.1. Mandatory-To-Implement metadata in each identity system
This table lists the metadata which is required to express a schema element in a particular identity system. If this metadata is not present for an attribute, then that attribute can't be represented correctly in a particular identity system. Being able to support these is necessary for identity schema mapping.

2.2. Metadata in RDF
This table lists the metadata from section 1 which already have representation as RDF predicates.