License Representation

This page describes how licenses are modeled and how a license list is parsed.

##Single License The class License in the spdx.document module represents a single license. A license has an identifier, a url and a full name. The URL property is simply the identifier prefixed with http://spdx.org/licenses/.

Conjunctive License Lists

The class LicenseConjuction in the spdx.document module represents a conjunction of two licenses. It's composed of two License instances license_1 and license_2. It's a subclass of License and overrides the identifier and full_name properties by simply adding an and between the properties of license_1 and license_2.

Disjunctive License Lists

The class LicenseDisjunction in the spdx.document module represents a disjunction of two licenses. It's composed of two License instances license_1 and license_2. It's a subclass of License and overrides the identifier and full_name properties by simply adding an or between the properties of license_1 and license_2.

Extracted License.

The class ExtractedLicense in the spdx.document module represents an extracted license in an spdx document.

License List Parsing

A license list value is a conjunction or disjunction of multiple licenses in the form: ( LicenseRef-1 and Apache-2.0 and LicenseRef-2) or ( LicenseRef-1 or Apache-2.0 or LicenseRef-2).

The spdx.utils.LicenseListLexer class uses ply.lex in order to convert a license list to a stream of tokens. It has the following tokens:

TOKEN	DESCRIPTION
LP	Left parenthesis
RP	Right parenthesis
AND	and
OR	or
LICENSE	License identifier

The spdx.utils.LicenseListParser class uses ply.yacc in order to parse the tokens returned by LicenseListLexer.

The LicenseListParser.parser method returns a LicenseConjuction or LicenseDisjunction instance that represents the 'root' of the license list. The licenses are grouped from right to left. The parse method returns None if there is a syntax error.

Grammar

license_list ::= LP conjuctions RP | LP disjunctions RP
conjuctions ::= conjuctions AND conjuction| conjuctions AND license|  conjuction
disjunctions ::= disjunctions OR disjunction | disjunctions OR license | disjunction
conjuction ::= license AND license
disjunction ::= license OR license
license ::= LICENSE

Notes:

• Non-terminals are lower case. Terminals upper case.
• license rule is for taking an action.

TODO:

• Granular LicenseListParser error reporting.