1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
|
---
layout: default
title: SPDX License Expressions
section: reference/licenses
---
# SPDX License Expressions
yotta module and target description files use [SPDX](http://spdx.org) License
Expression syntax to describe the licenses that apply to a module or target.
The full SPDX specification (currently version 2.0) is [available
here](http://spdx.org/sites/spdx/files/SPDX-2.0.pdf), but for ease of reference
the portion of the document referring to license expressions is included below.
It is a SPDX license-expression that should be used in the `license` fields
module.json and target.json files.
## Simple License Expressions
A simple **`<license-expression>`** is composed one of the following:
* An **SPDX License List Short Form Identifier**. For example: GPL-2.0
* An **SPDX License List Short Form Identifier** with a unary "+" operator
suffix to represent the current
version of the license or any later version. For example: GPL-2.0+
* A SPDX user defined license reference:
`["DocumentRef-"1*(idstring)":"]"LicenseRef- "1*(idstring)` Some examples:
LicenseRef-23
LicenseRef-MIT-Style-1
DocumentRef-spdx-tool-1.2:LicenseRef-MIT-Style-2
## Composite License Expressions
More expressive composite license expressions can be constructed using **"OR"**,
**"AND"**, and **"WITH"** operators similar to constructing mathematical expressions
using arithmetic operators. For the tag/value format, any license expression
that consists of more than one license identifier and/or LicenseRef, should be
encapsulated by parentheses: **"( )"**. This has been specified to facilitate
expression parsing. Nested parentheses can also be used to specify an order of
precedence which is discussed in more detail in subsection (4).
1. **Disjunctive "OR" Operator**
If presented with a choice between two or more licenses, use the
disjunctive binary **"OR"** operator to construct a new lincense
expression, where both the left and right operands are valid license
expression values.
For example, when given a choice between the LGPL-2.1 or MIT licenses, a
valid expression would be:
(LGPL-2.1 OR MIT)
An example representing a choice between three different licenses would be:
(LGPL-2.1 OR MIT OR BSD-3-Clause)
2. **Conjunctive "AND" Operator**
If required to simultaneously comply with two or more licenses, use the
conjunctive binary **"AND"** operator to construct a new license expression ,
where both the left and right operands are a valid license expression
values.
For example, when one is required to comply with both the LGPL-2.1 or MIT
licenses, a valid expression would be:
(LGPL-2.1 AND MIT)
An example where all three different licenses apply would be:
(LGPL-2.1 AND MIT AND BSD-2-Clause)
3. **Exception "WITH" Operator**
Sometimes a set of license terms apply except under special circumstances.
In this case, use the binary "WITH" operator to construct a new license
expression to represent the special exception situation. A valid
**`<license-expression>`** is where the left operand is a
**`<simple-expression>`** value and the right operand is a
**`<license-exception-id>`** that represents the special exception terms.
For example, when the Bison exception is to be applied to GPL-2.0+, the
expression would be:
(GPL-2.0+ WITH Bison-exception-2.2)
The current set of valid exceptions can be found in Appendix I, section 2.
For the most up to date set of exceptions please see spdx.org/licenses. If
the applicable exception is not found on the SPDX License Exception List,
then use a single **`<license-ref>`** to represent the entire license terms
(including the exception).
4. **Order of Precedence and Parentheses**
The order of application of the operators in an expression matters (similar
to mathematical operators). The default operator order of precedence of a
**`<license-expression>`** is:
1. **+**
2. **WITH**
3. **AND**
4. **OR**
where a lower order operator is applied before a higher order operator.
For example, the following expression: `LGPL-2.1 OR BSD-3-Clause AND MIT`
represents a license choice between either `LGPL-2.1` and the expression
`BSD-3-Clause AND MIT` because the `AND` operator takes precedence over (is
applied before) the `OR` operator.
When required to express an order of precedence that is different from the
default order a **`<license-expression>`** can be encapsulated in pairs of
parentheses: **( )**, to indicate that the operators found inside the
parentheses takes precedence over operators outside. This is also similar
to the use of parentheses in an algebraic expression e.g., (5+7)/2.
For instance, the following expression: `(MIT AND (LGPL-2.1+ OR BSD-3-Clause))`
states the OR operator should be applied before the AND operator. That is,
one should first select between the LGPL-2.1+ or the BSD-3-Clause license
before applying the MIT license.
## Examples
A yotta module which is licensed entirely and only under Apache-2.0 would use
this in its module.json file:
```json
{
"license": "Apache-2.0"
}
```
Or a module which contains both some code licensed under BSD, and other code
licensed under Apache-2.0 would use:
```json
{
"license": "(Apache-2.0 AND BSD)"
}
```
And a module which may be used at the user's choice under either a custom
license in the file LICENSE.txt, or under Apache-2.0, would use:
```json
{
"license": "(LicenseRef-LICENSE.txt OR Apache-2.0)"
}
```
If you have any questions about how to correctly describe the licenses that
apply to your module, please open an issue [on
Github](https://github.com/armmbed/yotta/issues).
**Note: some content on this page Copyright © 2010-2015 Linux Foundation and its Contributors. Licensed under the Creative Commons Attribution License 3.0 Unported. All other rights are expressly reserved. [Original source](http://spdx.org/sites/spdx/files/SPDX-2.0.pdf)**
|
