1.1 Terminology

The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, in this specification, are to be interpreted as described in [IETF RFC 2119].

The keywords expanded name, NCName and QName are to be interpreted as described in the XML Names specification [XML Names].

The keywords Unit Core Aspect are to be interpreted as described in the Open Information Model [OIM].

2.1 SQName

The Open Information Model makes extensive use of expanded names ([XML Names]) to provide globally unique identifiers. These are a namespace URI/localname pair. In order to reduce size and improve readability, it is convenient to use a QName-like mechanism for representing these (and some other) values, where the globally unique namespace-URI is replaced with a compact, document-scoped prefix. The mechanism used is referred to as an SQName ("Simplified QName").

An SQName is a compact, colon-separated represention of a URI/value pair, where a short, document-scoped, prefix is used to represent the URI.

An SQName has the following format:

prefix:localname

The prefix MUST be a valid NCName and MUST correspond to a key in the prefix map, and the namespace URI for identifier is taken from the corresponding value in the map.

Unlike QNames, the localname may be any string, including those containing the colon (":") character; the prefix and localname in an SQName are separated by the first colon character. Where an SQName is used to represent an expanded name, the localname will be a valid NCName.

A prefix map is a set of prefix/URI pairs that is used to resolve the prefix component of an SQName to a URI. The location and format of a prefix map is defined by the specification for the representation in which it is used, but it MUST conform to the following constraints:

1. The empty string MUST NOT be used as a prefix.
2. A URI MUST NOT be bound to more than one prefix within the map.
3. A prefix MUST NOT be bound to more than one URI within the map.
4. A reserved prefix MUST only be bound to the URI prescribed for that prefix.
5. A URI for which a reserved prefix is prescribed MUST NOT be bound to any other prefix.
6. Prefixes starting with the string xbrl MUST NOT be used unless they are reserved prefixes.

A reserved prefix is any prefix starting with with xbrl defined in any specification published by XBRL International, or any prefix identified as being reserved by the specification defining the inclusion of the prefix map.

SQNames are similar to QNames appearing within XML documents, but have the following differences, intended to make consumption simpler:

1. Unprefixed names are not permitted; there is no default namespace.
2. A URI may only be bound to a single prefix within a document.
3. A prefix may only be bound to a single URI within a document; prefixes may not be re-bound.

2.2 Unit string representation

The Unit Core Aspect defines units in terms of the combination of QNames by defining a list of numerators and a list of denominators. Reflecting this in concrete representations can be somewhat cumbersome, particularly as analysis the structure of units is expected to be a relatively uncommon operation compared to simply comparing units for equivalence, or rendering them to a user.

This section defines a standardised string representation for units, allowing units to be captured using a single, simple string value. This has the property that, provided that a consistent set of namespace prefixes are used, a given unit will have the single representation meaning that equivalence of units can be determined by a simple string comparison.

This representation is obtained as follows:

1. If {denominators} is not present, the SQNames representing the {numerators} are combined in lexicographic order, separated by the "*" character.
2. Otherwise, lists of {numerators} and {denominators} are created by combining SQNames in lexicographic order and separating with the "*" character, as above. If a list contains more than one item, the list is enclosed in parentheses, "(" and ")". The final string is then obtained by concatenating the list of numerators, the "/" character, and the list of denominators.

Whitespace is not permitted anywhere in the string representation, and the use of SQNames ensures that a 1:1 mapping between prefixes and namespaces is available thus ensuring that equivalent units appearing within the same document are represented with the same string.

Lexicograhic order means ordered based on comparison of Unicode code point values of each character.