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======== ========
You can point to objects present in the Software Heritage archive by the means You can point to objects present in the Software Heritage archive by the means
of **SoftWare Heritage persistent IDentifiers**, or **SWHIDs** for short, that of **SoftWare Heritage persistent IDentifiers**, or **SWHIDs** for short, that
are guaranteed to remain stable (persistent) over time. Their syntax, meaning, are guaranteed to remain stable (persistent) over time. Their syntax, meaning,
and usage is described below. Note that they are identifiers and not URLs, even and usage is described below. Note that they are identifiers and not URLs, even
though URL-based resolvers for SWHIDs are also available. though URL-based resolvers for SWHIDs are also available.
A SWHID can point to any software artifact (or "object") available in the A SWHID consists of two separate parts, a *core identifier* that can point to
Software Heritage archive. Objects come in different types: any software artifact (or "object") available in the Software Heritage archive,
and an *optional list of qualifiers* that allows to specify the context where
the object is meant to be seen, or point to a subpart of the object itself.
Objects come in different types:
* contents * contents
* directories * directories
* revisions * revisions
* releases * releases
* snapshots * snapshots
Each object is identified by an intrinsic, type-specific object identifier that Each object is identified by an intrinsic, type-specific object identifier that
is embedded in its SWHID as described below. The intrinsic identifiers embedded is embedded in its SWHID as described below. The intrinsic identifiers embedded
in SWHIDs are strong cryptographic hashes computed on the entire set of object in SWHIDs are strong cryptographic hashes computed on the entire set of object
properties. Together, these identifiers form a `Merkle structure properties. Together, these identifiers form a `Merkle structure
<https://en.wikipedia.org/wiki/Merkle_tree>`_, specifically a Merkle DAG. <https://en.wikipedia.org/wiki/Merkle_tree>`_, specifically a Merkle DAG.
See the :ref:`Software Heritage data model <data-model>` for an overview of See the :ref:`Software Heritage data model <data-model>` for an overview of
object types and how they are linked together. See object types and how they are linked together. See
:py:mod:`swh.model.identifiers` for details on how the intrinsic identifiers :py:mod:`swh.model.identifiers` for details on how the intrinsic identifiers
embedded in SWHIDs are computed. embedded in SWHIDs are computed.
The optional qualifiers are of two kinds:
* *context qualifiers* carry information about the context where a given
object is meant to be seen; this is particularly important, as the same object
can be reached in the Merkle graph following different *paths* from different
nodes (or *anchors*), and it may have been retrieved from different *origins*,
that may evolve between different *visits*,
* *fragment qualifiers* allow to pinpoint specific subparts of an object
Syntax Syntax
------ ------
Syntactically, SWHIDs are generated by the ``<identifier>`` entry point of the Syntactically, SWHIDs are generated by the ``<identifier>`` entry point of the
grammar: grammar:
.. code-block:: bnf .. code-block:: bnf
<identifier> ::= "swh" ":" <scheme_version> ":" <object_type> ":" <object_id> ; <identifier> ::= <identifier_core> [ <qualifierlist> ] ;
<identifier_core> ::= "swh" ":" <scheme_version> ":" <object_type> ":" <object_id> ;
<scheme_version> ::= "1" ; <scheme_version> ::= "1" ;
<object_type> ::= <object_type> ::=
"snp" (* snapshot *) "snp" (* snapshot *)
| "rel" (* release *) | "rel" (* release *)
| "rev" (* revision *) | "rev" (* revision *)
| "dir" (* directory *) | "dir" (* directory *)
| "cnt" (* content *) | "cnt" (* content *)
; ;
<object_id> ::= 40 * <hex_digit> ; (* intrinsic object id, as hex-encoded SHA1 *) <object_id> ::= 40 * <hex_digit> ; (* intrinsic object id, as hex-encoded SHA1 *)
<dec_digit> ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" <dec_digit> ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
<hex_digit> ::= <dec_digit> | "a" | "b" | "c" | "d" | "e" | "f" ; <hex_digit> ::= <dec_digit> | "a" | "b" | "c" | "d" | "e" | "f" ;
<qualifierlist> := <qualifier> [ <qualifierlist> ] ;
<qualifier> ::=
<context_qualifier>
| <fragment_qualifier>
;
<context_qualifier> ::=
<origin_ctxt>
| <visit_ctxt>
| <anchor_ctxt>
| <path_ctxt>
;
<origin_ctxt> ::= ";" "origin" "=" <url_escaped> ;
<visit_ctxt> ::= ";" "visit" "=" <identifier_core> ;
<anchor_ctxt> ::= ";" "anchor" "=" <identifier_core> ;
<path_ctxt> ::= ";" "path" "=" <path_absolute_escaped> ;
<fragment_qualifier> ::= ";" "lines" "=" <line_number> ["-" <line_number>] ;
<line_number> ::= <dec_digit> + ;
<url_escaped> ::= (* RFC 3986 compliant URLs, percent-escaped *)
<path_absolute_escaped> ::= (* RFC 3986 compliant absolute file path, percent-escaped *)
Where:
- ``<path_absolute_escaped>`` is an ``<ipath-absolute>`` from `RFC 3987`_, and
- ``<url_escaped>`` is a `RFC 3987`_ IRI
in either case all occurrences of ``;`` (and ``%``, as required by the RFC)
have been percent-encoded (as ``%3B`` and ``%25`` respectively). Other
characters *can* be percent-encoded, e.g., to improve readability and/or
embeddability of SWHID in other contexts.
.. _RFC 3987: https://tools.ietf.org/html/rfc3987
Semantics Semantics
--------- ---------
``:`` is used as separator between the logical parts of SWHIDs. The ``swh`` Core identifiers
~~~~~~~~~~~~~~~~
``:`` is used as separator between the logical parts of core identifiers. The ``swh``
prefix makes explicit that these identifiers are related to *SoftWare prefix makes explicit that these identifiers are related to *SoftWare
Heritage*. ``1`` (``<scheme_version>``) is the current version of this Heritage*. ``1`` (``<scheme_version>``) is the current version of this
identifier *scheme*; future editions will use higher version numbers, possibly identifier *scheme*; future editions will use higher version numbers, possibly
breaking backward compatibility (but without breaking the resolvability of breaking backward compatibility (but without breaking the resolvability of
SWHIDs that conform to previous versions of the scheme). SWHIDs that conform to previous versions of the scheme).
A SWHID points to a single object, whose type is explicitly captured by A SWHID points to a single object, whose type is explicitly captured by
``<object_type>``: ``<object_type>``:
* ``snp`` to **snapshots**, * ``snp`` to **snapshots**,
* ``rel`` to **releases**, * ``rel`` to **releases**,
* ``rev`` to **revisions**, * ``rev`` to **revisions**,
* ``dir`` to **directories**, * ``dir`` to **directories**,
* ``cnt`` to **contents**. * ``cnt`` to **contents**.
The actual object pointed to is identified by the intrinsic identifier The actual object pointed to is identified by the intrinsic identifier
``<object_id>``, which is a hex-encoded (using lowercase ASCII characters) SHA1 ``<object_id>``, which is a hex-encoded (using lowercase ASCII characters) SHA1
computed on the content and metadata of the object itself, as follows: computed on the content and metadata of the object itself, as follows:
* for **snapshots**, intrinsic identifiers are computed as per * for **snapshots**, intrinsic identifiers are computed as per
:py:func:`swh.model.identifiers.snapshot_identifier` :py:func:`swh.model.identifiers.snapshot_identifier`
* for **releases**, as per * for **releases**, as per
:py:func:`swh.model.identifiers.release_identifier` :py:func:`swh.model.identifiers.release_identifier`
that produces the same result as a git release hash
* for **revisions**, as per * for **revisions**, as per
:py:func:`swh.model.identifiers.revision_identifier` :py:func:`swh.model.identifiers.revision_identifier`
that produces the same result as a git commit hash
* for **directories**, as per * for **directories**, per
:py:func:`swh.model.identifiers.directory_identifier` :py:func:`swh.model.identifiers.directory_identifier`
that produces the same result as a git tree hash
* for **contents**, the intrinsic identifier is the ``sha1_git`` hash of the * for **contents**, the intrinsic identifier is the ``sha1_git`` hash returned by
multiple hashes returned by
:py:func:`swh.model.identifiers.content_identifier`, i.e., the SHA1 of a byte :py:func:`swh.model.identifiers.content_identifier`, i.e., the SHA1 of a byte
sequence obtained by juxtaposing the ASCII string ``"blob"`` (without sequence obtained by juxtaposing the ASCII string ``"blob"`` (without
quotes), a space, the length of the content as decimal digits, a NULL byte, quotes), a space, the length of the content as decimal digits, a NULL byte,
and the actual content of the file. and the actual content of the file.
Qualifiers
~~~~~~~~~~
``;`` is used as separator between the core identifier and the optional
qualifiers, and optional qualifiers. Each qualifier is specified as a
key/value pair, using ``=`` as a separator.
The following *context qualifiers* are available:
* **origin** : the *software origin* where an object has been found or observed
in the wild, as an URI;
* **visit** : the core identifier of a *snapshot* corresponding to a specific
*visit* of a repository containing the designated object;
* **anchor** : a *designated node* in the Merkle DAG relative to which a *path
to the object* is specified, as the core identifier of a directory, a
revision, a release or a snapshot;
* **path** : the *absolute file path*, from the *root directory* associated to
the *anchor node*, to the object; when the anchor denotes a directory or a
revision, and almost always when it's a release, the root directory is
uniquely determined; when the anchor denotes a snapshot, the root directory
is the one pointed to by ``HEAD`` (possibly indirectly), and undefined if
such a reference is missing;
The following *fragment qualifier* is available:
* **lines** : *line number(s)* of interest, usually within a content object
We recommend to equip identifiers meant to be shared with as many qualifiers as
possible. While qualifiers may be listed in any order, it is good practice to
present them in the order given above, i.e., ``origin``, ``visit``, ``anchor``,
``path``, ``lines``. Redundant information should be omitted: for example, if
the *visit* is present, and the *path* is relative to the snapshot indicated
there, then the *anchor* qualifier is superfluous; similarly, if the *path* is
empty, it may be omitted.
Git compatibility Git compatibility
~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~
SWHIDs for contents, directories, revisions, and releases are, at present, SWHIDs for contents, directories, revisions, and releases are, at present,
compatible with the `Git <https://git-scm.com/>`_ way of `computing identifiers compatible with the `Git <https://git-scm.com/>`_ way of `computing identifiers
<https://git-scm.com/book/en/v2/Git-Internals-Git-Objects>`_ for its objects. <https://git-scm.com/book/en/v2/Git-Internals-Git-Objects>`_ for its objects.
A SWHID for a content object will correspond (in its ``<object_id>`` part) to a The ``<object_id>`` part of a SWHID for a content object is the Git blob
Git blob identifier of any file with the same content; a SWHID for a revision identifier of any file with the same content; for a revision it is the Git
will correspond to the Git commit identifier for the same revision, etc. This commit identifier for the same revision, etc. This is not the case for snapshot
is not the case for snapshot identifiers, as Git does not have a corresponding identifiers, as Git does not have a corresponding object type.
object type.
Note that Git compatibility is incidental and is not guaranteed to be Note that Git compatibility is incidental and is not guaranteed to be
maintained in future versions of this scheme (or Git). maintained in future versions of this scheme (or Git).
Examples Examples
-------- --------
Core identifiers
~~~~~~~~~~~~~~~~
* ``swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2`` points to the content * ``swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2`` points to the content
of a file containing the full text of the GPL3 license of a file containing the full text of the GPL3 license
* ``swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505`` points to a directory * ``swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505`` points to a directory
containing the source code of the Darktable photography application as it was containing the source code of the Darktable photography application as it was
at some point on 4 May 2017 at some point on 4 May 2017
* ``swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d`` points to a commit in * ``swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d`` points to a commit in
the development history of Darktable, dated 16 January 2017, that added the development history of Darktable, dated 16 January 2017, that added
undo/redo supports for masks undo/redo supports for masks
* ``swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f`` points to Darktable * ``swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f`` points to Darktable
release 2.3.0, dated 24 December 2016 release 2.3.0, dated 24 December 2016
* ``swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453`` points to a snapshot * ``swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453`` points to a snapshot
of the entire Darktable Git repository taken on 4 May 2017 from GitHub of the entire Darktable Git repository taken on 4 May 2017 from GitHub
Identifiers with qualifiers
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Contextual information * The following `fully qualified SWHID <https://archive.softwareheritage.org/swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;;origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;path=/Examples/SimpleFarm/simplefarm.ml;lines=9-15>`_ denotes the lines 9 to 15 of a file content that can be found at absolute path ``/Examples/SimpleFarm/simplefarm.ml`` from the root directory of the revision ``swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0`` that is contained in the snapshot ``swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9`` taken from the origin ``https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git``
======================
The SWHIDs as described above are *intrinsic identifiers*, as they are computed
from the designated object itself, and it is often useful to provide
*contextual information* about a particular occurrence of the object, like the
origin from where the object has been found. To this end, SWHIDs can be
coupled with **qualifiers** that capture such *contextual information*.
Qualifiers come in different kinds:
* origin
* visit
* anchor
* path
* lines
Syntax
------
The full-syntax to complement SWHIDs with contextual information is given by
the ``<identifier_with_context>`` entry point of the grammar:
.. code-block:: bnf
<identifier_with_context> ::= <identifier> [ <qualifierlist> ]
<qualifierlist> := <qualifier> [ <qualifierlist> ]
<qualifier> ::= <origin_ctxt> | <visit_ctxt> | <anchor_ctxt> | <path_ctxt> |<lines_ctxt>
<origin_ctxt> ::= ";" "origin" "=" <url_escaped>
<visit_ctxt> ::= ";" "visit" "=" <identifier>
<anchor_ctxt> ::= ";" "anchor" "=" <identifier>
<path_ctxt> ::= ";" "path" "=" <path_absolute_escaped>
<lines_ctxt> ::= ";" "lines" "=" <line_number> ["-" <line_number>]
<line_number> ::= <dec_digit> +
<url_escaped> ::= (* RFC 3986 compliant URLs, percent-escaped *)
<path_absolute_escaped> ::= (* RFC 3986 compliant absolute file path, percent-escaped *)
Where:
- ``<path_absolute_escaped>`` is an ``<ipath-absolute>`` from `RFC 3987`_, and
- ``<url_escaped>`` is a `RFC 3987`_ IRI
in either case all occurrences of ``;`` (and ``%``, as required by the RFC)
have been percent-encoded (as ``%3B`` and ``%25`` respectively). Other
characters *can* be percent-encoded, e.g., to improve readability and/or
embeddability of SWHID in other contexts.
.. _RFC 3987: https://tools.ietf.org/html/rfc3987
Semantics
---------
``;`` is used as separator between SWHIDs and the optional contextual
information qualifiers. Each contextual information qualifier is specified as a
key/value pair, using ``=`` as a separator.
The following piece of contextual information are supported:
* **origin** : the *software origin* where an object has been found or observed
in the wild, as an URI;
* **visit** : persistent identifier of a *snapshot* corresponding to a specific
*visit* of a repository containing the designated object;
* **anchor** : a *designated node* in the Merkle DAG relative to which a *path
to the object* is specified, as a persistent identifier of a directory, a
revision, a release or a snapshot;
* **path** : the *absolute file path*, from the *root directory* associated to
the *anchor node*, to the object; when the anchor denotes a directory or a
revision, and almost always when it's a release, the root directory is
uniquely determined; when the anchor denotes a snapshot, the root directory
is the one pointed to by ``HEAD`` (possibly indirectly), and undefined if
such a reference is missing;
* **lines** : *line number(s)* of interest, usually within a content object
We recommend to equip identifiers meant to be shared with as many qualifiers as
possible. While qualifiers may be listed in any order, it is good practice to
present them in the order given above, i.e., ``origin``, ``visit``, ``anchor``,
``path``, ``lines``. Redundant information should be omitted: for example, if
the *visit* is present, and the *path* is relative to the snapshot indicated
there, then the *anchor* qualifier is superfluous.
Example
-------
The following `fully qualified SWHID
<https://archive.softwareheritage.org/swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;;origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;path=/Examples/SimpleFarm/simplefarm.ml;lines=9-15>`_
denotes the lines 9 to 15 of a file content that can be found at absolute path
``/Examples/SimpleFarm/simplefarm.ml`` from the root directory of the revision
``swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0`` that is contained in the
snapshot ``swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9`` taken from the
origin ``https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git``.
.. code-block:: url .. code-block:: url
swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b; swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;
origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git; origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;
visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9; visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;
anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0; anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;
path=/Examples/SimpleFarm/simplefarm.ml; path=/Examples/SimpleFarm/simplefarm.ml;
lines=9-15 lines=9-15
And this is an example of `a fully qualified SWHID with a percent escaped file * This is an example of `a fully qualified SWHID with a percent escaped file path <https://archive.softwareheritage.org/swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;origin=https://github.com/web-platform-tests/wpt;visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/>`_
path
<https://archive.softwareheritage.org/swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;origin=https://github.com/web-platform-tests/wpt;visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/>`_
.. code-block:: url .. code-block:: url
swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04; swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;
origin=https://github.com/web-platform-tests/wpt; origin=https://github.com/web-platform-tests/wpt;
visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499; visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;
anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96; anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;
path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/ path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/
Resolution Computing and resolving SWHIDs
========== ==============================
An important property of SWHIDs is that a core identifier is *intrinsic*: it can
be *computed from the object itself* using the `swh-identify <https://docs.softwareheritage.org/devel/swh-model/cli.html>`_ utility, or equivalently using standard git tools.
This has various practical implications:
* when a software artifact is obtained from Software Heritage by resolving a
SWHID, it is straightforward to verify that it is exactly the intended one:
just compute the core identifier from the artefact itself, and check that it
is the same as the core identifier part of the SHWID
Dedicated resolvers * the core identifier of a software artifact can be computed *before* its archival on
------------------- Software Heritage
Resolvers
---------
SWHIDs can be resolved using the Software Heritage Web application (see SWHIDs can be resolved using the Software Heritage Web application (see
:py:mod:`swh.web`). In particular, the **root endpoint** ``/`` can be given a :py:mod:`swh.web`). In particular, the **root endpoint** ``/`` can be given a
SWHID and will lead to the browsing page of the corresponding object, like SWHID and will lead to the browsing page of the corresponding object, like
this: ``https://archive.softwareheritage.org/<identifier>``. this: ``https://archive.softwareheritage.org/<identifier>``.
A **dedicated** ``/resolve`` **endpoint** of the HTTP API is also available to A **dedicated** ``/resolve`` **endpoint** of the HTTP API is also available to
explicitly request SWHID resolution; see: :http:get:`/api/1/resolve/(swh_id)/`. explicitly request SWHID resolution; see: :http:get:`/api/1/resolve/(swh_id)/`.
Examples: Examples:
* `<https://archive.softwareheritage.org/swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2>`_ * `<https://archive.softwareheritage.org/swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2>`_
* `<https://archive.softwareheritage.org/swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505>`_ * `<https://archive.softwareheritage.org/swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505>`_
* `<https://archive.softwareheritage.org/api/1/resolve/swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d>`_ * `<https://archive.softwareheritage.org/api/1/resolve/swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d>`_
* `<https://archive.softwareheritage.org/api/1/resolve/swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f>`_ * `<https://archive.softwareheritage.org/api/1/resolve/swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f>`_
* `<https://archive.softwareheritage.org/api/1/resolve/swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453>`_ * `<https://archive.softwareheritage.org/api/1/resolve/swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453>`_
* `<https://archive.softwareheritage.org/swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;;origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;path=/Examples/SimpleFarm/simplefarm.ml;lines=9-15>`_
* `<https://archive.softwareheritage.org/swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;origin=https://github.com/web-platform-tests/wpt;visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/>`_
External resolvers External resolvers
------------------ ~~~~~~~~~~~~~~~~~~
The following **independent resolvers** support resolution of SWHIDs: The following **independent resolvers** support resolution of SWHIDs:
* `Identifiers.org <https://identifiers.org>`_; see: * `Identifiers.org <https://identifiers.org>`_; see:
`<http://identifiers.org/swh/>`_ (registry identifier `MIR:00000655 `<http://identifiers.org/swh/>`_ (registry identifier `MIR:00000655
<https://www.ebi.ac.uk/miriam/main/datatypes/MIR:00000655>`_). <https://www.ebi.ac.uk/miriam/main/datatypes/MIR:00000655>`_).
* `Name-to-Thing (N2T) <https://n2t.net/>`_ * `Name-to-Thing (N2T) <https://n2t.net/>`_
Examples: Examples:
* `<https://identifiers.org/swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2>`_ * `<https://identifiers.org/swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2>`_
* `<https://identifiers.org/swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505>`_ * `<https://identifiers.org/swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505>`_
* `<https://identifiers.org/swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d>`_ * `<https://identifiers.org/swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d>`_
* `<https://n2t.net/swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f>`_ * `<https://n2t.net/swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f>`_
* `<https://n2t.net/swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453>`_ * `<https://n2t.net/swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453>`_
* `<https://n2t.net/swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;;origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;path=/Examples/SimpleFarm/simplefarm.ml;lines=9-15>`_
* `<https://n2t.net/swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;origin=https://github.com/web-platform-tests/wpt;visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/>`_
Note that resolution via Identifiers.org does not support contextual Note that resolution via Identifiers.org currently only supports *core identifiers* due to `syntactic incompatibilities with qualifiers <http://identifiers.org/documentation#custom_requests>`_.
information, due to `syntactic incompatibilities
<http://identifiers.org/documentation#custom_requests>`_.
References References
========== ==========
* Roberto Di Cosmo, Morane Gruenpeter, Stefano Zacchiroli. `Identifiers for * Roberto Di Cosmo, Morane Gruenpeter, Stefano Zacchiroli. `Identifiers for
Digital Objects: the Case of Software Source Code Preservation Digital Objects: the Case of Software Source Code Preservation
<https://hal.archives-ouvertes.fr/hal-01865790v4>`_. In Proceedings of `iPRES <https://hal.archives-ouvertes.fr/hal-01865790v4>`_. In Proceedings of `iPRES
2018 <https://ipres2018.org/>`_: 15th International Conference on Digital 2018 <https://ipres2018.org/>`_: 15th International Conference on Digital
Preservation, Boston, MA, USA, September 2018, 9 pages. Preservation, Boston, MA, USA, September 2018, 9 pages.
* Roberto Di Cosmo, Morane Gruenpeter, Stefano Zacchiroli. `Referencing Source * Roberto Di Cosmo, Morane Gruenpeter, Stefano Zacchiroli. `Referencing Source
Code Artifacts: a Separate Concern in Software Citation Code Artifacts: a Separate Concern in Software Citation
<https://arxiv.org/abs/2001.08647>`_. In Computing in Science and <https://arxiv.org/abs/2001.08647>`_. In Computing in Science and
Engineering, volume 22, issue 2, pages 33-43. ISSN 1521-9615, Engineering, volume 22, issue 2, pages 33-43. ISSN 1521-9615,
IEEE. March 2020. IEEE. March 2020.
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