Application Extension Bundle description Language (AEBL)
draft-tclarke-aebl-00

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Abstract

This memo presents an RDF (, “Resource Description Framework (RDF),” .) [refs.RDF] vocabulary for describing an application extension bundle (Clarke, T., “Application Extension Bundle (AEB),” July 2008.) [refs.aeb]. An application extension bundle, otherwise known as an add-on, extension, plug-in, suite, or package, is an encapsalation of all the data needed to add functionality to a plug-in based application. An integral piece of an application extension bundle is the metadata describing the bundle. The described RDF vocabulary contains required and optional metadata fields used by an application extension bundle to describe itself.

Table of Contents

1.  Introduction
    1.1.  Relationship to XPI
    1.2.  A Note on Examples
2.  AEBL Namespace and primary subject
3.  Verbs
    3.1.  Required
        3.1.1.  id
        3.1.2.  version
        3.1.3.  type
        3.1.4.  name
        3.1.5.  targetApplication
    3.2.  Optional
        3.2.1.  description
        3.2.2.  creator
        3.2.3.  developer
        3.2.4.  translator
        3.2.5.  contributor
        3.2.6.  homepageURL
        3.2.7.  iconURL
        3.2.8.  licenseURL
        3.2.9.  hidden
        3.2.10.  targetPlatform
        3.2.11.  requires
        3.2.12.  incompatible
        3.2.13.  updateURL
        3.2.14.  updateKey
4.  versions
5.  The aeb URL Scheme
6.  Updates
    6.1.  Verbs
        6.1.1.  signature
        6.1.2.  updates
7.  Example
8.  References
§  Author's Address
§  Intellectual Property and Copyright Statements

1.  Introduction

An application extension bundle (AEB) (Clarke, T., “Application Extension Bundle (AEB),” July 2008.) [refs.aeb] encapsulates all the data required to extend an application. Often referred to as a plug-in or add-on, an AEB is a specific format designed to be application and platform agnostic. An application accepting an AEB is referred to as a target application. A key component of an AEB is descriptive metadata such as the AEB version, requirements, authors, etc. The application extension bundle description language (AEBL) is an RDF (, “Resource Description Framework (RDF),” .) [refs.RDF] vocabulary for the metadata needed by an AEB.

1.1.  Relationship to XPI

The AEBL vocabulary is based on an RDF vocabulary used by the Mozilla XPInstall (, “Mozilla XPInstall,” .) [refs.XPInstall] addon system, sometimes known as XPI. XPI is a compelling format containing much of the metadata needed for an AEB. However, the XPI format is tightly coupled to the Mozilla project and the description documents often refer to specific XPI engine implementation details. AEB and the AEBL standardize XPI and remove the Mozilla specific details. The original version of AEBL is nearly an exact copy of the XPI format with minor changes and clarifications. AEBL should, however, be considered a fork of XPI and further changes to XPI may not be reflected in AEBL.

1.2.  A Note on Examples

Examples presented in this document will be presented in specific serializations of RDF such as rdf+xml and Notation3 (Berners-Lee, T., “A Notation3 Primer,” .) [refs.N3Primer]. The AEBL vocabulary is not restricted to these specific serializaions and any valid RDF serialization format should be considered equally valid for use with AEBL. Specific implementations of AEBL may be restricted to one or more serializations.

All examples assume the following prefixes

@prefix rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix aebl: <urn:2008:03:aebl-syntax-ns#>.

2.  AEBL Namespace and primary subject

AEBL elements are defined in the AEBL namespace. The AEBL namespace is urn:2008:03:aebl-syntax-ns. This namespace is subject to change before acceptance of this Internet Draft as an RFC. The primary subject (the analog of an XML root element) is urn:aebl:install-manifest.

3.  Verbs

3.1.  Required

3.1.1.  id

A unique identifier for the AEB.

• A UUID (, “Information technology -- Open Systems Interconnection -- Remote Procedure Call (RPC),” .) [refs.UUID] in the form {00000000-0000-0000-0000-000000000000}
• An Internet email (Klensin, J., Ed., “Simple Mail Transfer Protocol,” April 2001.) [refs.email] style address as a string. This need not represent an existing email account but uses the same format. Ex. aebname@organization.tld

The id shall not change when the version of an AEB changes. Version information is stored in the version (version) verb.

The following regular expression matches an id.

^([A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4})|((\{{0,1}([0-9a-fA-F]){8}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){12}\}{0,1}))$

3.1.2.  version

The version verb identifies the version of the AEB. The format of the object shall conform to the specification in the version numbers (versions) section.

3.1.3.  type

The type verb indicates the type of extension stored in the AEB. Valid types are listed below.

2

Functionality extensions and general extensions not fitting another category

4

Themes and skins which change the look of a GUI application

8

Locale and language extensions which add additional natural language translations

32

Multiple item AEB (Clarke, T., “Application Extension Bundle (AEB),” July 2008.) [refs.aeb]

>=16384

Types defined for a specific target application

3.1.4.  name

The name verb indentifies the name of this AEB. This is designed to be presented to a user and shall not be used for comparison or unique identification purposes. The id (id) verb is used to uniquely identify an AEB.

3.1.5.  targetApplication

This verb defines a potential target application. There must be at least one targetApplication defined in an AEB and there may be multiple targetApplications defined in an AEB.

<urb:aebl:install-manifest> aebl:targetApplication [ aebl:id "{00000000-0000-0000-0000-000000000000}" ].

3.1.5.1.  id

This identifies the target application. The format is identical to the main id (id) verb.

3.1.5.2.  minVersion

This identifies the minimum version of the target application required. The format is the same as the version (version) verb.

3.1.5.3.  maxVersion

This identifies the maximum version of the target application required. The format is the same as the version (version) verb.

3.2.  Optional

3.2.1.  description

This is a short description of the AEB intended for display to the user. This should fit on one short line of text. A specific target application may impose more strict length requirements.

3.2.2.  creator

The creator verb identifies the name for the creator or prinicipal developer of the AEB. This is inteded for display to the user.

3.2.3.  developer

The developer verb identifies an additional developer of the AEB. The principal developer should be named with the creator (creator) verb. Additional developers are named with the developer verb. There must be one and only one creator (creator) verb if a developer verb is present. There is no limit to the number of developer verbs allowed but a target application may provide more strict limits. This is intended for display to the user.

3.2.4.  translator

The translator verb identifies language translators. There is no limit to the number of translator verbs allowed but a target application may provide more strict limits. This is intended for display to the user.

3.2.5.  contributor

The contributor verb identifies additional contributor to the AEB. There is no limit to the number of contributor verbs allowed but a target application may provide more strict limits. This is intended for display to the user.

3.2.6.  homepageURL

The URL for the AEB's homepage. If present, this must be a valid URL. This is intended for display to the user.

3.2.7.  iconURL

The URL for a 32x32 pixel icon intended for display to the user. This will typically be displayed in a list of AEBs in the target application. The icon should be a common image file format such as PNG, JPG, or ICO. A target application may further restrict the acceptable file types. Target applications must accept the AEB URL scheme (The aeb URL Scheme) and may accept other URL schemes.

3.2.8.  licenseURL

The URL for a file containing license text. This is intended for display to the user. A target application may display this in any way but this will typically be displayed in an "accept/reject" dialog box during AEB installation. A target application must accept plain text files in UTF-8 format and may accept other file formats. A target application must accept the AEB URL scheme (The aeb URL Scheme) and may accept other URL schemes. There is no limit to the number of licenseURL verbs preset. All licenseURL files must be displayed but a target application may use any ordering.

3.2.9.  hidden

This is a boolean value. If true, the AEB is considered a hidden AEB. A target application should not display this AEB in a list of installed AEBs. A target application may have a way to enable the display of hidden AEBs. This is intended to prevent the user from seeing or removing AEBs which are considered a core piece of a target application. Care should be used when marking an AEB as hidden. A target application may disallow hidden AEBs. The value is case insensitive. Valid positive values are: 1, t, and true. Valid negative values are: 0, f, and false.

3.2.10.  targetPlatform

This specifies the target platform for this AEB. There is no limit to the number of targetPlatform verbs allowed. This should contain either an operating system target or a complete application binary interface (ABI) target. A target application defines valid target strings. Some examples are WINNT, Linux, i686-pc-linux-gnu, and x86_64-msvc8.

3.2.11.  requires

This verb identifies another AEB requirement of this AEB. The format is identical to targetApplication (targetApplication) but the target id refers to an AEB id. There is no limit to the number of requires allowed. A target application may install the AEB if a required target is not present but should disable the AEB until the target becomes available. In addition to the id (id), minVersion (minVersion), and maxVersion (maxVersion) verbs, requires may contain a targetApplication verb.

3.2.11.1.  targetApplication

The format of this verb is identical to the higher level targetApplication (targetApplication) verb. It is used to further restrict a requires (requires). If present, it indicates that the requires only applies when the target application meets the specification of targetApplication. This is intended to specify AEB requirements which are different depending on the target application of the AEB.

3.2.12.  incompatible

This verb identifies extensions which are incompatible with this AEB. The format is identical to requires (requires) but the identified extension and version must not be present in the target application.

3.2.13.  updateURL

This URL provides an update manifest file with information about AEB updates. This URL should use the https scheme. If a non-secure scheme is specified, an updateKey (updateKey) should be specified. Further information on the format of this URL is presented in updates (Updates).

3.2.14.  updateKey

This contains a base64 encoded public key used to verify update signatures. The key is comprised of the encryption algorithm identifier, following by a colon then the base64 encoding. The data contained in the encoding is specific to the encryption algorithm identifier. A target application which does not support the specified encryption algorithm must refuse updates for this AEB. There may be multiple updateKey verbs each providing a key for a different encryption algorith. It is suggested that the updateURL (updateURL) use the https scheme and the updateKey verb not be used. Further information is presented in updates (Updates).

An example updateKey

<urb:aebl:install-manifest> aebl:updateKey "x509:MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDK426erD/H3XtsjvaB5+PJqbhj
                                                    Zc9EDI5OCJS8R3FIObJ9ZHJK1TXeaE7JWqt9WUmBWTEFvwS+FI9vWu8058N9CHhD
                                                    NyeP6i4LuUYjTURnn7Yw/IgzyIJ2oKsYa32RuxAyteqAWqPT/J63wBixIeCxmysf
                                                    awB/zH4KaPiY3vnrzQIDAQAB".

4.  versions

Version numbers are period separated version fields. A target application or AEB defines the specific meaning of various version fields. This document defines the format and comparison rules only. There must be at least one version field and there is no limit to the number of allowed version fields. Each version field is comprised of four parts: abcd. Parts a and c are integers greater than or equal to 0. Parts b and d are ASCII encoded strings. Part a is required. If part b, c or d is present, all parts to the left are required. A part may be an asterisk (*) indicating an infinite value for that part and is greater than all other values allowed for that part except * which is equal. If a part contains a * the parts to the right shall be ignored.

The following regular expression matches a version.

^(((-?\d+)|\*)((([a-zA-Z+_]+)|\*)(((-?\d+)|\*)(([a-zA-Z+_]+)|\*)?)?)?)(\.((-?\d+)|\*)((([a-zA-Z+_]+)|\*)(((-?\d+)|\*)(([a-zA-Z+_]+)|\*)?)?)?)*$

1.-1 < 1 == 1.0 == 1.0.0 < 1.1a < 1.1aa < 1.1ab < 1.1b < 1.1c
1.1c < 1.1foo < 1.1pre == 1.1pre0 < 1.1pre1a < 1.1pre1aa < 1.1pre1b < 1.1pre1
1.1pre1 < 1.1pre2 < 1.1pre10 < 1.1.-1 < 1.1
1.1 == 1.1.0 == 1.1.00 < 1.10 < 1.* < 1.*.1 < 2.0

5.  The aeb URL Scheme

The aeb URL scheme (for example aeb:///icons/small.png) is used to reference files stored in an AEB. The root of an aeb URL refers to the root of the AEB archive as defined in [refs.aeb] (Clarke, T., “Application Extension Bundle (AEB),” July 2008.).

6.  Updates

An AEB may specify an updateURL (updateURL) which will return an update manifest. If the URL scheme supports MIME types (such as http and https) the MIME type of the update manifest must be a valid RDF MIME type such as text/rdf+xml. A target application may limit which RDF MIME types are accepted. The updateURL may contain the following values which will be substituted before requesting the manifest. Substitutions will be encoded as valid URLs.

%REQ_VERSION%

The request format version. Currently this is 1

%AEB_ID%

The id (id) of this AEB

%AEB_VERSION%

The version (version) of the AEB

%AEB_MAXAPPVERSION%

The maxVersion (maxVersion) specified in the AEB of the targetApplication requesting the update manifest

%AEB_STATUS%

A comma separated list of the status of installed AEBs. Each field is the id of the AEB, an equals (=) and a status string. A target application defines the status strings. If the corresponding status is supported by a target application, it should use the following strings.

userEnabled

The AEB is enabled and functional.

userDisabled

The user has disabled the AEB.

incompatible

The AEB is installed but is disabled because it is not compatible with either the target application version or one or more AEB versions.

blocksListed

If the AEB target of the update manifest request is disabled due to incompatibility of another AEB version, this AEB is cause. Multiple AEBs may have this status.

needsDependencies

The AEB is installed but is disabled because it is missing one or more AEB dependencies.

%APP_ID%

The id (id) of the target application requesting the update manifest

%APP_VERSION%

The version of the target application requesting the update manifest

%APP_TARGET%

The OS and ABI platform of the target application requesting the update manifest. The specific format is defined by the target application.

%APP_LOCALE%

The locale of the target application requesting the update manifest

The update manifest is an RDF file simlar to an install manifest. The namespace is the same as an install manifest and the primary subject is urn:aebl:update-manifest:aebid where aebid is the id (id) of the AEB.

6.1.  Verbs

6.1.1.  signature

This contains the base64 encoded signature of the update manifest. This has the same format as updateKey (updateKey). There may be multiple signature verbs which correspond to multiple updateKey verbs in the install manifest. The algorithm for generating and verifying a signature is determined by the cryptographic algorithm. The portion of the update that should be signed is the updates (updates) group.

6.1.2.  updates

This contains an RDF list with one list element per AEB version defined in the update manifest.

6.1.2.1.  version

This declares the version of the AEB for this list element.

6.1.2.2.  targetApplication

This declares the target application for this list element. There may be multiple targetApplication tags. The format is the same as Section 3.1.5 (targetApplication) with the addition of the following verbs.

6.1.2.2.1.  updateURL

This is the URL for the AEB corresponding to this version (version) and targetApplication (targetApplication) combination.

6.1.2.2.2.  updateInfoURL

This is a URL for an informational page about this updated AEB. This is intended for display to the user.

6.1.2.2.3.  updateSignature

This is the signature of the data obtained from Section 6.1.2.2.1 (updateURL). This is not needed if the URL scheme is secure (such as https) and follows the same rules and suggestions as signature (signature).

An example update manifest

<?xml version="1.0" encoding="UTF-8"?>

<RDF:RDF xmlns:RDF="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:aebl="urn:2008:03:aebl-syntax-ns#">

  <RDF:Description about="urn:aebl:update-manifest:foobar@developer.org">
    <aebl:updates>
      <RDF:Seq>
        <!-- Each li is a different version of the same AEB -->
        <RDF:li>
          <RDF:Description>
            <aebl:version>2.2</aebl:version> <!-- This is the version number of the AEB -->

            <!-- One targetApplication for each application the AEB is compatible with -->
            <aebl:targetApplication>
              <RDF:Description>
                <aebl:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</aebl:id>
                <aebl:minVersion>1.5</aebl:minVersion>
                <aebl:maxVersion>2.0.0.*</aebl:maxVersion>

                <!-- This is where this version of the AEB will be downloaded from -->
                <aebl:updateURL>https://www.mysite.com/foobar2.2.aeb</aebl:updateURL>

                <!-- A page describing what is new in this updated version -->
                <aebl:updateInfoURL>http://www.mysite.com/updateinfo2.2.xhtml</aebl:updateInfoURL>
              </RDF:Description>
            </aebl:targetApplication>
          </RDF:Description>
        </RDF:li>

        <RDF:li>
          <RDF:Description>
            <aebl:version>2.5</aebl:version>
            <aebl:targetApplication>
              <RDF:Description>
                <aebl:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</aebl:id>
                <aebl:minVersion>1.5</aebl:minVersion>
                <aebl:maxVersion>2.0.0.*</aebl:maxVersion>
                <aebl:updateURL>http://www.mysite.com/foobar2.5.aeb</aebl:updateURL>
                <aebl:updateHash>sha1:78fc1d2887eda35b4ad2e3a0b60120ca271ce6e6</aebl:updateHash>
              </RDF:Description>
            </aebl:targetApplication>
          </RDF:Description>
        </RDF:li>

      </RDF:Seq>
    </aebl:updates>

    <!-- A signature is only necessary if your AEB includes an updateKey
         in its install.rdf. -->
    <aebl:signature>x509:MIGTMA0GCSqGSIb3DQEBBQUAA4GBAMO1O2gwSCCth1GwYMgscfaNakpN40PJfOWt
                  ub2HVdg8+OXMciF8d/9eVWm8eH/IxuxyZlmRZTs3O5tv9eWAY5uBCtqDf1WgTsGk
                  jrgZow1fITkZI7w0//C8eKdMLAtGueGfNs2IlTd5P/0KH/hf1rPc1wUqEqKCd4+L
                  BcVq13ad</aebl:signature>
  </RDF:Description>
</RDF:RDF>

7.  Example

@prefix rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix aebl: <urn:2008:03:aebl-syntax-ns#> .

<urn:aebl:install-manifest>
   aebl:id "{00000000-0000-0000-0000-000000000000}" ;
   aebl:name "Test AEB" ;
   aebl:version "1.2.3b" ;
   aebl:type "2" ;
   aebl:description "This is a test" ;
   aebl:creator "Trevor Clarke" ;
   aebl:updateURL "https://www.foo.bar/ack" ;
   aebl:iconURL "aeb:///icons/small.png" ;
   aebl:licenseURL "aeb:///licenses/lgpl.txt" ;
   aebl:licenseURL "aeb:///licenses/creativecommons.txt" ;
   aebl:targetApplication [
      aebl:id "{12345678-0000-0000-0000-000000000000}" ;
      aebl:minVersion "1.2" ;
      aebl:maxVersion "1.*" ] ;
   aebl:targetPlatform "WINNT-x86_64-msvc8" .

8. References

Author's Address

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